This document summarizes a study that uses 3D hydrodynamic simulations and 1D stellar evolution modeling to investigate the merger of a 16 solar mass star with a 4 solar mass companion star. The simulations show the companion spirals inward and merges with the primary star's helium core. Approximately 0.6 solar masses of material is ejected in an asymmetric, bipolar outflow. The post-merger structure is then modeled in 1D stellar evolution, showing in some cases the star evolves to have surface properties similar to Betelgeus, with rapid rotation and enhanced nitrogen at the surface. This pioneering study aims to comprehensively model stellar mergers across dynamical, thermal, and nuclear evolutionary timescales.
Tidal star-planet interaction and its observed impact on stellar activity in ...Sérgio Sacani
This study investigates tidal star-planet interaction by analyzing X-ray observations of planet-hosting stars that are part of wide binary systems. The study compares the X-ray luminosity, an indicator of stellar activity, between the planet-hosting primary star and its non-planet hosting companion star. By analyzing 34 such binary systems with X-ray data from XMM-Newton and Chandra, the study finds that planet hosts with close-in massive planets have higher X-ray luminosity compared to their companion stars, indicating tidal interaction is altering the rotation and magnetic activity of the host stars. The study concludes tidal interaction from massive, close-in planets can impact the rotational evolution of stars, while more distant or smaller planets likely
The SAMI Galaxy Sur v ey: galaxy spin is more strongly correlated with stella...Sérgio Sacani
We use the SAMI Galaxy Surv e y to examine the drivers of galaxy spin, λR e , in a multidimensional parameter space including stellar mass, stellar population age (or specific star formation rate), and various environmental metrics (local density, halo mass, satellite versus central). Using a partial correlation analysis, we consistently find that age or specific star formation rate is the primary parameter correlating with spin. Light-weighted age and specific star formation rate are more strongly correlated with spin than mass-weighted age. In fact, across our sample, once the relation between light-weighted age and spin is accounted for, there is no significant residual correlation between spin and mass, or spin and environment. This result is strongly suggestive that the present-day environment only indirectly influences spin, via the removal of gas and star formation quenching. That is, environment affects age, then age affects spin. Older galaxies then have lower spin, either due to stars being born dynamically hotter at high redshift, or due to secular heating. Our results appear to rule out environmentally dependent dynamical heating (e.g. g alaxy–g alaxy interactions) being important, at least within 1 R e where our kinematic measurements are made. The picture is more complex when we only consider high-mass galaxies ( M ∗ ≳ 10 11 M ). While the age-spin relation is still strong for these high-mass galaxies, there is a residual environmental trend with central galaxies preferentially having lower spin, compared to satellites of the same age and mass. We argue that this trend is likely due to central galaxies being a preferred location for mergers.
The SPHERE view of three interacting twin disc systems in polarised lightSérgio Sacani
Dense stellar environments as hosts of ongoing star formation increase the probability of gravitational encounters among stellar
systems during the early stages of evolution. Stellar interaction may occur through non-recurring, hyperbolic or parabolic passages
(a so-called ‘fly-by’), through secular binary evolution, or through binary capture. In all three scenarios, the strong gravitational
perturbation is expected to manifest itself in the disc structures around the individual stars. Here, we present near-infrared
polarised light observations that were taken with the SPHERE/IRDIS instrument of three known interacting twin-disc systems:
AS 205, EM* SR 24, and FU Orionis. The scattered light exposes spirals likely caused by the gravitational interaction. On
a larger scale, we observe connecting filaments between the stars. We analyse their very complex polarised intensity and put
particular attention to the presence of multiple light sources in these systems. The local angle of linear polarisation indicates
the source whose light dominates the scattering process from the bridging region between the two stars. Further, we show
that the polarised intensity from scattering with multiple relevant light sources results from an incoherent summation of the
individuals’ contribution. This can produce nulls of polarised intensity in an image, as potentially observed in AS 205.We discuss
the geometry and content of the systems by comparing the polarised light observations with other data at similar resolution,
namely with ALMA continuum and gas emission. Collective observational data can constrain the systems’ geometry and stellar
trajectories, with the important potential to differentiate between dynamical scenarios of stellar interaction.
Formation of low mass protostars and their circumstellar disksSérgio Sacani
Understanding circumstellar disks is of prime importance in astrophysics, however, their birth process remains poorly constrained due to observational and numerical challenges. Recent numerical works have shown that the small-scale physics, often wrapped into a sub-grid model, play a crucial role in disk formation and evolution. This calls for a combined approach in which both the protostar and circumstellar disk are studied in concert. Aims. We aim to elucidate the small scale physics and constrain sub-grid parameters commonly chosen in the literature by resolving the star-disk interaction. Methods. We carry out a set of very high resolution 3D radiative-hydrodynamics simulations that self-consistently describe the collapse of a turbulent dense molecular cloud core to stellar densities. We study the birth of the protostar, the circumstellar disk, and its early evolution (< 6 yr after protostellar formation). Results. Following the second gravitational collapse, the nascent protostar quickly reaches breakup velocity and sheds its surface material, thus forming a hot (∼ 103 K), dense, and highly flared circumstellar disk. The protostar is embedded within the disk, such that material can flow without crossing any shock fronts. The circumstellar disk mass quickly exceeds that of the protostar, and its kinematics are dominated by self-gravity. Accretion onto the disk is highly anisotropic, and accretion onto the protostar mainly occurs through material that slides on the disk surface. The polar mass flux is negligible in comparison. The radiative behavior also displays a strong anisotropy, as the polar accretion shock is shown to be supercritical whereas its equatorial counterpart is subcritical. We also f ind a remarkable convergence of our results with respect to initial conditions. Conclusions. These results reveal the structure and kinematics in the smallest spatial scales relevant to protostellar and circumstellar disk evolution. They can be used to describe accretion onto regions commonly described by sub-grid models in simulations studying larger scale physics.
Disks of Stars in the Galactic Center Triggered by Tidal Disruption EventsSérgio Sacani
This document proposes that tidal disruption events (TDEs) from wandering stars could trigger episodes of positive star formation feedback in the Galactic Center, providing an explanation for the observed disks of young stars near Sgr A*. When a star is tidally disrupted by the supermassive black hole, the resulting jet compresses gas clouds to densities high enough to resist tidal forces and form stars within the disk plane perpendicular to the jet. The estimated rate of jetted TDEs is consistent with the age of the disk stars. This mechanism predicts a random orientation for each disk and the potential for multiple misaligned disks from separate TDE events.
Extensive Pollution of Uranus and Neptune’s Atmospheres by Upsweep of Icy Mat...Sérgio Sacani
In the Nice model of solar system formation, Uranus and Neptune undergo an orbital upheaval,
sweeping through a planetesimal disk. The region of the disk from which material is accreted by
the ice giants during this phase of their evolution has not previously been identified. We perform
direct N-body orbital simulations of the four giant planets to determine the amount and origin of solid
accretion during this orbital upheaval. We find that the ice giants undergo an extreme bombardment
event, with collision rates as much as ∼3 per hour assuming km-sized planetesimals, increasing the
total planet mass by up to ∼0.35%. In all cases, the initially outermost ice giant experiences the
largest total enhancement. We determine that for some plausible planetesimal properties, the resulting
atmospheric enrichment could potentially produce sufficient latent heat to alter the planetary cooling
timescale according to existing models. Our findings suggest that substantial accretion during this
phase of planetary evolution may have been sufficient to impact the atmospheric composition and
thermal evolution of the ice giants, motivating future work on the fate of deposited solid material.
Os astrônomos descobriram um processo único sobre como as maiores galáxias elípticas do universo continuam gerando estrelas muito tempo depois do anos de pico de nascimentos estelares. A alta resolução e a sensibilidade à radiação ultravioleta do Hubble, permitiu aos astrônomos observarem nós brilhantes de estrelas azuis, quentes, se formando juntamente com jatos de buracos negros ativos encontrados nos centros das gigantescas galáxias elípticas.
Combinando dados do Huubble com observações feitas por um conjunto de telescópios baseados tanto em Terra como no espaço, duas equipes independentes descobriram que os jatos dos buracos negros, e as estrelas recém-nascidas são todos partes de um ciclo auto-regulado. Jatos de alta energia atirados do buraco negro aquecem um halo de gás circulante, controlando a taxa com a qual o gás esfria e cai na galáxia.
“Pense no gás ao redor da galáxia como uma atmosfera”, explicou o líder do primeiro estudo, Megan Donahue, da Universidade Estadual do Michigan. “Essa atmosfera pode conter material em diferentes estados, do mesmo modo que a nossa atmosfera tem gás, nuvens e chuva. O que nós estamos vendo é um processo parecido com uma tempestade. À medida que os jatos impulsionam o gás para fora do centro da galáxia, parte do gás esfria e precipita em aglomerados frios que caem de volta para o centro da galáxia como gotas de chuvas”.
“As gotas de chuva eventualmente esfriam o suficiente para tornar-se nuvens de formação de estrelas de gás frio molecular, e a capacidade de observar no ultravioleta distante do Hubble, nos permitiu observar diretamente esses chuviscos de formação de estrelas”, explicou o líder do segundo estudo, Grant Tremblay, da Universidade de Yale. “Nós sabemos que esses chuviscos estão linkados com os jatos, pois eles foram encontrados em filamentos que se dobram ao redor dos jatos, ou abraçam as bordas de bolhas gigantes que os jatos inflaram”, disse Tremblay. “E eles terminam fazendo um redemoinho de gás de formação de estrelas ao redor do buraco negro central”.
Modelling element abundances_in_semi_analytic_models_of_galaxy_formationSérgio Sacani
This document summarizes a new implementation of detailed chemical enrichment modeling in the Munich semi-analytic model of galaxy formation (L-Galaxies). The new implementation tracks the delayed enrichment of 11 heavy elements from stellar winds, supernovae type II, and supernovae type Ia. It considers different supernovae type II yield sets and three supernovae type Ia delay-time distributions. The results are compared to observational data on local star-forming galaxies, Milky Way disc G dwarfs, and local elliptical galaxies. Overall, the best model matches require a power-law supernovae type Ia delay-time distribution, supernovae type II yields accounting for prior mass loss, and some direct ejection
Tidal star-planet interaction and its observed impact on stellar activity in ...Sérgio Sacani
This study investigates tidal star-planet interaction by analyzing X-ray observations of planet-hosting stars that are part of wide binary systems. The study compares the X-ray luminosity, an indicator of stellar activity, between the planet-hosting primary star and its non-planet hosting companion star. By analyzing 34 such binary systems with X-ray data from XMM-Newton and Chandra, the study finds that planet hosts with close-in massive planets have higher X-ray luminosity compared to their companion stars, indicating tidal interaction is altering the rotation and magnetic activity of the host stars. The study concludes tidal interaction from massive, close-in planets can impact the rotational evolution of stars, while more distant or smaller planets likely
The SAMI Galaxy Sur v ey: galaxy spin is more strongly correlated with stella...Sérgio Sacani
We use the SAMI Galaxy Surv e y to examine the drivers of galaxy spin, λR e , in a multidimensional parameter space including stellar mass, stellar population age (or specific star formation rate), and various environmental metrics (local density, halo mass, satellite versus central). Using a partial correlation analysis, we consistently find that age or specific star formation rate is the primary parameter correlating with spin. Light-weighted age and specific star formation rate are more strongly correlated with spin than mass-weighted age. In fact, across our sample, once the relation between light-weighted age and spin is accounted for, there is no significant residual correlation between spin and mass, or spin and environment. This result is strongly suggestive that the present-day environment only indirectly influences spin, via the removal of gas and star formation quenching. That is, environment affects age, then age affects spin. Older galaxies then have lower spin, either due to stars being born dynamically hotter at high redshift, or due to secular heating. Our results appear to rule out environmentally dependent dynamical heating (e.g. g alaxy–g alaxy interactions) being important, at least within 1 R e where our kinematic measurements are made. The picture is more complex when we only consider high-mass galaxies ( M ∗ ≳ 10 11 M ). While the age-spin relation is still strong for these high-mass galaxies, there is a residual environmental trend with central galaxies preferentially having lower spin, compared to satellites of the same age and mass. We argue that this trend is likely due to central galaxies being a preferred location for mergers.
The SPHERE view of three interacting twin disc systems in polarised lightSérgio Sacani
Dense stellar environments as hosts of ongoing star formation increase the probability of gravitational encounters among stellar
systems during the early stages of evolution. Stellar interaction may occur through non-recurring, hyperbolic or parabolic passages
(a so-called ‘fly-by’), through secular binary evolution, or through binary capture. In all three scenarios, the strong gravitational
perturbation is expected to manifest itself in the disc structures around the individual stars. Here, we present near-infrared
polarised light observations that were taken with the SPHERE/IRDIS instrument of three known interacting twin-disc systems:
AS 205, EM* SR 24, and FU Orionis. The scattered light exposes spirals likely caused by the gravitational interaction. On
a larger scale, we observe connecting filaments between the stars. We analyse their very complex polarised intensity and put
particular attention to the presence of multiple light sources in these systems. The local angle of linear polarisation indicates
the source whose light dominates the scattering process from the bridging region between the two stars. Further, we show
that the polarised intensity from scattering with multiple relevant light sources results from an incoherent summation of the
individuals’ contribution. This can produce nulls of polarised intensity in an image, as potentially observed in AS 205.We discuss
the geometry and content of the systems by comparing the polarised light observations with other data at similar resolution,
namely with ALMA continuum and gas emission. Collective observational data can constrain the systems’ geometry and stellar
trajectories, with the important potential to differentiate between dynamical scenarios of stellar interaction.
Formation of low mass protostars and their circumstellar disksSérgio Sacani
Understanding circumstellar disks is of prime importance in astrophysics, however, their birth process remains poorly constrained due to observational and numerical challenges. Recent numerical works have shown that the small-scale physics, often wrapped into a sub-grid model, play a crucial role in disk formation and evolution. This calls for a combined approach in which both the protostar and circumstellar disk are studied in concert. Aims. We aim to elucidate the small scale physics and constrain sub-grid parameters commonly chosen in the literature by resolving the star-disk interaction. Methods. We carry out a set of very high resolution 3D radiative-hydrodynamics simulations that self-consistently describe the collapse of a turbulent dense molecular cloud core to stellar densities. We study the birth of the protostar, the circumstellar disk, and its early evolution (< 6 yr after protostellar formation). Results. Following the second gravitational collapse, the nascent protostar quickly reaches breakup velocity and sheds its surface material, thus forming a hot (∼ 103 K), dense, and highly flared circumstellar disk. The protostar is embedded within the disk, such that material can flow without crossing any shock fronts. The circumstellar disk mass quickly exceeds that of the protostar, and its kinematics are dominated by self-gravity. Accretion onto the disk is highly anisotropic, and accretion onto the protostar mainly occurs through material that slides on the disk surface. The polar mass flux is negligible in comparison. The radiative behavior also displays a strong anisotropy, as the polar accretion shock is shown to be supercritical whereas its equatorial counterpart is subcritical. We also f ind a remarkable convergence of our results with respect to initial conditions. Conclusions. These results reveal the structure and kinematics in the smallest spatial scales relevant to protostellar and circumstellar disk evolution. They can be used to describe accretion onto regions commonly described by sub-grid models in simulations studying larger scale physics.
Disks of Stars in the Galactic Center Triggered by Tidal Disruption EventsSérgio Sacani
This document proposes that tidal disruption events (TDEs) from wandering stars could trigger episodes of positive star formation feedback in the Galactic Center, providing an explanation for the observed disks of young stars near Sgr A*. When a star is tidally disrupted by the supermassive black hole, the resulting jet compresses gas clouds to densities high enough to resist tidal forces and form stars within the disk plane perpendicular to the jet. The estimated rate of jetted TDEs is consistent with the age of the disk stars. This mechanism predicts a random orientation for each disk and the potential for multiple misaligned disks from separate TDE events.
Extensive Pollution of Uranus and Neptune’s Atmospheres by Upsweep of Icy Mat...Sérgio Sacani
In the Nice model of solar system formation, Uranus and Neptune undergo an orbital upheaval,
sweeping through a planetesimal disk. The region of the disk from which material is accreted by
the ice giants during this phase of their evolution has not previously been identified. We perform
direct N-body orbital simulations of the four giant planets to determine the amount and origin of solid
accretion during this orbital upheaval. We find that the ice giants undergo an extreme bombardment
event, with collision rates as much as ∼3 per hour assuming km-sized planetesimals, increasing the
total planet mass by up to ∼0.35%. In all cases, the initially outermost ice giant experiences the
largest total enhancement. We determine that for some plausible planetesimal properties, the resulting
atmospheric enrichment could potentially produce sufficient latent heat to alter the planetary cooling
timescale according to existing models. Our findings suggest that substantial accretion during this
phase of planetary evolution may have been sufficient to impact the atmospheric composition and
thermal evolution of the ice giants, motivating future work on the fate of deposited solid material.
Os astrônomos descobriram um processo único sobre como as maiores galáxias elípticas do universo continuam gerando estrelas muito tempo depois do anos de pico de nascimentos estelares. A alta resolução e a sensibilidade à radiação ultravioleta do Hubble, permitiu aos astrônomos observarem nós brilhantes de estrelas azuis, quentes, se formando juntamente com jatos de buracos negros ativos encontrados nos centros das gigantescas galáxias elípticas.
Combinando dados do Huubble com observações feitas por um conjunto de telescópios baseados tanto em Terra como no espaço, duas equipes independentes descobriram que os jatos dos buracos negros, e as estrelas recém-nascidas são todos partes de um ciclo auto-regulado. Jatos de alta energia atirados do buraco negro aquecem um halo de gás circulante, controlando a taxa com a qual o gás esfria e cai na galáxia.
“Pense no gás ao redor da galáxia como uma atmosfera”, explicou o líder do primeiro estudo, Megan Donahue, da Universidade Estadual do Michigan. “Essa atmosfera pode conter material em diferentes estados, do mesmo modo que a nossa atmosfera tem gás, nuvens e chuva. O que nós estamos vendo é um processo parecido com uma tempestade. À medida que os jatos impulsionam o gás para fora do centro da galáxia, parte do gás esfria e precipita em aglomerados frios que caem de volta para o centro da galáxia como gotas de chuvas”.
“As gotas de chuva eventualmente esfriam o suficiente para tornar-se nuvens de formação de estrelas de gás frio molecular, e a capacidade de observar no ultravioleta distante do Hubble, nos permitiu observar diretamente esses chuviscos de formação de estrelas”, explicou o líder do segundo estudo, Grant Tremblay, da Universidade de Yale. “Nós sabemos que esses chuviscos estão linkados com os jatos, pois eles foram encontrados em filamentos que se dobram ao redor dos jatos, ou abraçam as bordas de bolhas gigantes que os jatos inflaram”, disse Tremblay. “E eles terminam fazendo um redemoinho de gás de formação de estrelas ao redor do buraco negro central”.
Modelling element abundances_in_semi_analytic_models_of_galaxy_formationSérgio Sacani
This document summarizes a new implementation of detailed chemical enrichment modeling in the Munich semi-analytic model of galaxy formation (L-Galaxies). The new implementation tracks the delayed enrichment of 11 heavy elements from stellar winds, supernovae type II, and supernovae type Ia. It considers different supernovae type II yield sets and three supernovae type Ia delay-time distributions. The results are compared to observational data on local star-forming galaxies, Milky Way disc G dwarfs, and local elliptical galaxies. Overall, the best model matches require a power-law supernovae type Ia delay-time distribution, supernovae type II yields accounting for prior mass loss, and some direct ejection
Kinematics and simulations_of_the_stellar_stream_in_the_halo_of_the_umbrella_...Sérgio Sacani
This document summarizes a study of the stellar stream and substructures around the Umbrella Galaxy (NGC 4651). Deep imaging and spectroscopy were used to characterize the properties and kinematics of the stream. Tracer objects like globular clusters and planetary nebulae were identified and found to delineate a kinematically cold feature in position-velocity space. Dynamical modeling suggests the stream originated from the tidal disruption of a dwarf galaxy on a highly eccentric orbit about 6-10 billion years ago. This work demonstrates the feasibility of using discrete tracers to recover the kinematics and model the dynamics of low surface brightness stellar streams around distant galaxies.
Detection of anisotropic satellite quenching in galaxy clusters up to z ∼ 1Sérgio Sacani
Satellite galaxies in the cluster environment are more likely to be quenched than galaxies in the general field. Recently, it has
been reported that satellite galaxy quenching depends on the orientation relative to their central galaxies: satellites along the
major axis of centrals are more likely to be quenched than those along the minor axis. In this paper, we report a detection
of such anisotropic quenching up to z ∼ 1 based on a large optically selected cluster catalogue constructed from the Hyper
Suprime-Cam Subaru Strategic Program. We calculate the quiescent satellite galaxy fraction as a function of orientation angle
measured from the major axis of central galaxies and find that the quiescent fractions at 0.25 < z < 1 are reasonably fitted
by sinusoidal functions with amplitudes of a few per cent. Anisotropy is clearer in inner regions (<r200m) of clusters and not
significant in cluster outskirts (>r200m). We also confirm that the observed anisotropy cannot be explained by differences in
local galaxy density or stellar mass distribution along the two axes. Quiescent fraction excesses between the two axes suggest
that the quenching efficiency contributing to the anisotropy is almost independent of stellar mass, at least down to our stellar
mass limit of M∗ = 1 × 1010 M. Finally, we argue that the physical origins of the observed anisotropy should have shorter
quenching time-scales than ∼ 1 Gyr, like ram-pressure stripping, because, for anisotropic quenching to be observed, satellites
must be quenched before their initial orientation angles are significantly changed.
HST imaging of star-forming clumps in 6 GASP ram-pressure stripped galaxiesSérgio Sacani
Exploiting broad- and narrow-band images of the Hubble Space Telescope from near-UV to I-band
restframe, we study the star-forming clumps of six galaxies of the GASP sample undergoing strong
ram-pressure stripping (RPS). Clumps are detected in Hα and near-UV, tracing star formation on
different timescales. We consider clumps located in galaxy disks, in the stripped tails and those
formed in stripped gas but still close to the disk, called extraplanar. We detect 2406 Hα-selected
clumps (1708 in disks, 375 in extraplanar regions, and 323 in tails) and 3750 UV-selected clumps (2026
disk clumps, 825 extraplanar clumps and 899 tail clumps). Only ∼ 15% of star-forming clumps are
spatially resolved, meaning that most are smaller than ∼ 140 pc. We study the luminosity and size
distribution functions (LDFs and SDFs, respectively) and the luminosity-size relation. The average
LDF slope is 1.79 ± 0.09, while the average SDF slope is 3.1 ± 0.5. Results suggest the star formation
to be turbulence driven and scale-free, as in main-sequence galaxies. All the clumps, whether they are
in the disks or in the tails, have an enhanced Hα luminosity at a given size, compared to the clumps in
main-sequence galaxies. Indeed, their Hα luminosity is closer to that of clumps in starburst galaxies,
indicating that ram pressure is able to enhance the luminosity. No striking differences are found among
disk and tail clumps, suggesting that the different environments in which they are embedded play a
minor role in influencing the star formation.
HST imaging of star-forming clumps in 6 GASP ram-pressure stripped galaxiesSérgio Sacani
Exploiting broad- and narrow-band images of the Hubble Space Telescope from near-UV to I-band
restframe, we study the star-forming clumps of six galaxies of the GASP sample undergoing strong
ram-pressure stripping (RPS). Clumps are detected in Hα and near-UV, tracing star formation on
different timescales. We consider clumps located in galaxy disks, in the stripped tails and those
formed in stripped gas but still close to the disk, called extraplanar. We detect 2406 Hα-selected
clumps (1708 in disks, 375 in extraplanar regions, and 323 in tails) and 3750 UV-selected clumps (2026
disk clumps, 825 extraplanar clumps and 899 tail clumps). Only ∼ 15% of star-forming clumps are
spatially resolved, meaning that most are smaller than ∼ 140 pc. We study the luminosity and size
distribution functions (LDFs and SDFs, respectively) and the luminosity-size relation. The average
LDF slope is 1.79 ± 0.09, while the average SDF slope is 3.1 ± 0.5. Results suggest the star formation
to be turbulence driven and scale-free, as in main-sequence galaxies. All the clumps, whether they are
in the disks or in the tails, have an enhanced Hα luminosity at a given size, compared to the clumps in
main-sequence galaxies. Indeed, their Hα luminosity is closer to that of clumps in starburst galaxies,
indicating that ram pressure is able to enhance the luminosity. No striking differences are found among
disk and tail clumps, suggesting that the different environments in which they are embedded play a
minor role in influencing the star formation.
HST imaging of star-forming clumps in 6 GASP ram-pressure stripped galaxiesSérgio Sacani
Exploiting broad- and narrow-band images of the Hubble Space Telescope from near-UV to I-band
restframe, we study the star-forming clumps of six galaxies of the GASP sample undergoing strong
ram-pressure stripping (RPS). Clumps are detected in Hα and near-UV, tracing star formation on
different timescales. We consider clumps located in galaxy disks, in the stripped tails and those
formed in stripped gas but still close to the disk, called extraplanar. We detect 2406 Hα-selected
clumps (1708 in disks, 375 in extraplanar regions, and 323 in tails) and 3750 UV-selected clumps (2026
disk clumps, 825 extraplanar clumps and 899 tail clumps). Only ∼ 15% of star-forming clumps are
spatially resolved, meaning that most are smaller than ∼ 140 pc. We study the luminosity and size
distribution functions (LDFs and SDFs, respectively) and the luminosity-size relation. The average
LDF slope is 1.79 ± 0.09, while the average SDF slope is 3.1 ± 0.5. Results suggest the star formation
to be turbulence driven and scale-free, as in main-sequence galaxies. All the clumps, whether they are
in the disks or in the tails, have an enhanced Hα luminosity at a given size, compared to the clumps in
main-sequence galaxies. Indeed, their Hα luminosity is closer to that of clumps in starburst galaxies,
indicating that ram pressure is able to enhance the luminosity. No striking differences are found among
disk and tail clumps, suggesting that the different environments in which they are embedded play a
minor role in influencing the star formation.
The pillars of_creation_revisited_with_muse_gas_kinematics_and_high_mass_stel...Sérgio Sacani
The document discusses observations of the Pillars of Creation in the Eagle Nebula using integral field spectroscopy from the MUSE instrument on the VLT. For the first time, the study maps physical parameters like extinction, density, temperature, and velocity across the pillars. The data show that the pillar tips have high densities and are being photoevaporated by the massive stars in NGC 6611. The kinematics indicate a blueshifted photoevaporative flow, consistent with simulations. The 3D geometry of the pillars is inferred, with some in front of and some behind the ionizing stars. A previously unknown outflow is detected from the middle pillar, suggesting an embedded protostar.
Is Betelgeuse Really Rotating? Synthetic ALMA Observations of Large-scale Con...Sérgio Sacani
The evolved stages of massive stars are poorly understood, but invaluable constraints can be derived from spatially resolved observations of nearby red supergiants, such as Betelgeuse. Atacama Large Millimeter/submillimeter Array (ALMA) observations of Betelgeuse showing a dipolar velocity field have been interpreted as evidence for a projected rotation rate of about 5 km s−1. This is 2 orders of magnitude larger than predicted by single-star evolution, which led to suggestions that Betelgeuse is a binary merger. We propose instead that large-scale convective motions can mimic rotation, especially if they are only partially resolved. We support this claim with 3D CO5BOLDsimulations of nonrotating red supergiants that we postprocessed to predict ALMA images and SiO spectra. We show that our synthetic radial velocity maps have a 90% chance of being falsely interpreted as evidence for a projected rotation rate of 2 km s−1 or larger for our fiducial simulation. We conclude that we need at least another ALMA observation to firmly establish whether Betelgeuse is indeed rapidly rotating. Such observations would also provide insight into the role of angular momentum and binary interaction in the late evolutionary stages. The data will further probe the structure and complex physical processes in the atmospheres of red supergiants, which are immediate progenitors of supernovae and are believed to be essential in the formation of gravitational-wave sources.
This study analyzed high-resolution spectra of 125 compact stellar systems (CSSs) in the giant elliptical galaxy NGC 5128 to measure their radial velocities and velocity dispersions. Combining these measurements with structural parameters from imaging, dynamical masses were derived for 112 CSSs, including 89 for the first time. Two distinct sequences were found in the dynamical mass-to-light ratio vs dynamical mass plane, which can be approximated by power laws. The shallower sequence corresponds to bright globular clusters, while the steeper relation appears to be populated by objects requiring significant dark matter such as central black holes or concentrated dark matter. This suggests different formation histories for these CSSs compared to classical globular clusters in NGC 5128 and
The Variable Detection of Atmospheric Escape around the Young, Hot Neptune AU...Sérgio Sacani
This document summarizes observations from the Hubble Space Telescope of the young hot Neptune exoplanet AU Mic b, which orbits the nearby M dwarf star AU Mic. The observations aimed to detect atmospheric escape of neutral hydrogen through absorption in the stellar Lyman-alpha emission line. Two visits were obtained, one in 2020 and one in 2021, corresponding to transits of the planet. A stellar flare was observed and removed from the first visit data. In the second visit, absorption was detected in the blue wing of the Lyman-alpha line 2.5 hours before the white light transit, indicating the presence of high-velocity neutral hydrogen escaping the planet's atmosphere and traveling toward the observer. Estimates place the column density of this material
Asymmetrical tidal tails of open star clusters: stars crossing their cluster’...Sérgio Sacani
The document discusses asymmetrical tidal tails observed around five open star clusters, which challenges Newtonian gravity. It summarizes how tidal tails form as stars escape clusters due to energy equipartition. Observations of the Hyades, Praesepe, Coma Berenices, COIN-Gaia 13, and NGC 752 clusters found more stars in the leading tidal tails within 50 pc of the clusters. Simulations show that in Newtonian gravity, tidal tails should be symmetrical, but asymmetries can arise in Milgromian dynamics. Future work is needed to better map tidal tails and develop Milgromian simulations.
UV and Hα HST observations of 6 GASP jellyfish galaxiesSérgio Sacani
Star-forming, Hα-emitting clumps are found embedded in the gaseous tails of galaxies undergoing
intense ram pressure stripping in galaxy clusters, so-called jellyfish galaxies. These clumps offer a
unique opportunity to study star formation under extreme conditions, in the absence of an underlying
disk and embedded within the hot intracluster medium. Yet, a comprehensive, high spatial resolution
study of these systems is missing. We obtained UVIS/HST data to observe the first statistical sample
of clumps in the tails and disks of six jellyfish galaxies from the GASP survey; we used a combination
of broad-band (UV to I) filters and a narrow-band Hα filter. HST observations are needed to study
the sizes, stellar masses and ages of the clumps and their clustering hierarchy. These observations will
be used to study the clump scaling relations, the universality of the star formation process and verify
whether a disk is irrelevant, as hinted by jellyfish galaxy results. This paper presents the observations,
data reduction strategy, and some general results based on the preliminary data analysis. The UVIS
high spatial resolution gives an unprecedented sharp view of the complex structure of the inner regions
of the galaxies and of the substructures in the galaxy disks. We found clear signatures of stripping
in regions very close in projection to the galactic disk. The star-forming regions in the stripped tails
are extremely bright and compact while we did not detect a significant number of star-forming clumps
outside those detected by MUSE. The paper finally presents the development plan for the project.
UV and Hα HST observations of 6 GASP jellyfish galaxiesSérgio Sacani
Star-forming, Hα-emitting clumps are found embedded in the gaseous tails of galaxies undergoing
intense ram pressure stripping in galaxy clusters, so-called jellyfish galaxies. These clumps offer a
unique opportunity to study star formation under extreme conditions, in the absence of an underlying
disk and embedded within the hot intracluster medium. Yet, a comprehensive, high spatial resolution
study of these systems is missing. We obtained UVIS/HST data to observe the first statistical sample
of clumps in the tails and disks of six jellyfish galaxies from the GASP survey; we used a combination
of broad-band (UV to I) filters and a narrow-band Hα filter. HST observations are needed to study
the sizes, stellar masses and ages of the clumps and their clustering hierarchy. These observations will
be used to study the clump scaling relations, the universality of the star formation process and verify
whether a disk is irrelevant, as hinted by jellyfish galaxy results. This paper presents the observations,
data reduction strategy, and some general results based on the preliminary data analysis. The UVIS
high spatial resolution gives an unprecedented sharp view of the complex structure of the inner regions
of the galaxies and of the substructures in the galaxy disks. We found clear signatures of stripping
in regions very close in projection to the galactic disk. The star-forming regions in the stripped tails
are extremely bright and compact while we did not detect a significant number of star-forming clumps
outside those detected by MUSE. The paper finally presents the development plan for the project.
UV and Hα HST observations of 6 GASP jellyfish galaxiesSérgio Sacani
Star-forming, Hα-emitting clumps are found embedded in the gaseous tails of galaxies undergoing
intense ram pressure stripping in galaxy clusters, so-called jellyfish galaxies. These clumps offer a
unique opportunity to study star formation under extreme conditions, in the absence of an underlying
disk and embedded within the hot intracluster medium. Yet, a comprehensive, high spatial resolution
study of these systems is missing. We obtained UVIS/HST data to observe the first statistical sample
of clumps in the tails and disks of six jellyfish galaxies from the GASP survey; we used a combination
of broad-band (UV to I) filters and a narrow-band Hα filter. HST observations are needed to study
the sizes, stellar masses and ages of the clumps and their clustering hierarchy. These observations will
be used to study the clump scaling relations, the universality of the star formation process and verify
whether a disk is irrelevant, as hinted by jellyfish galaxy results. This paper presents the observations,
data reduction strategy, and some general results based on the preliminary data analysis. The UVIS
high spatial resolution gives an unprecedented sharp view of the complex structure of the inner regions
of the galaxies and of the substructures in the galaxy disks. We found clear signatures of stripping
in regions very close in projection to the galactic disk. The star-forming regions in the stripped tails
are extremely bright and compact while we did not detect a significant number of star-forming clumps
outside those detected by MUSE. The paper finally presents the development plan for the project.
GRMHD Simulations of Neutron-star Mergers with Weak Interactions: r-process N...Sérgio Sacani
Fast neutron-rich material ejected dynamically over 10 ms during the merger of a binary neutron star (BNS) can
give rise to distinctive electromagnetic counterparts to the system’s gravitational-wave emission that serve as a
“smoking gun” to distinguish between a BNS and an NS–black hole merger. We present novel ab initio modeling
of the kilonova precursor and kilonova afterglow based on 3D general-relativistic magnetohydrodynamic
simulations of BNS mergers with nuclear, tabulated, finite-temperature equations of state (EOSs), weak
interactions, and approximate neutrino transport. We analyze dynamical mass ejection from 1.35–1.35 Me
binaries, consistent with properties of the first observed BNS merger GW170817, using three nuclear EOSs that
span the range of allowed compactness of 1.35 Me-neutron stars. Nuclear reaction network calculations yield a
robust second-to-third-peak r-process. We find few ×10−6 Me of fast (v > 0.6c) ejecta that give rise to broadband
synchrotron emission on ∼years timescales, consistent with tentative evidence for excess X-ray/radio emission
following GW170817. We find ≈2 × 10−5 Me of free neutrons that power a kilonova precursor on hours
timescale. A boost in early UV/optical brightness by a factor of a few due to previously neglected relativistic
effects, with enhancements up to 10 hr post-merger, is promising for future detection with UV/optical telescopes
like Swift or ULTRASAT. We find that a recently predicted opacity boost due to highly ionized lanthanides at
70,000 K is unlikely to affect the early kilonova based on the obtained ejecta structures. Azimuthal
inhomogeneities in dynamical ejecta composition for soft EOSs found here (“lanthanide/actinide pockets”) may
have observable consequences for both early kilonova and late-time nebular emission.
Third epoch magellanic_clouud_proper_motionsSérgio Sacani
The document analyzes proper motion data from the Hubble Space Telescope to study the three-dimensional rotation field of the Large Magellanic Cloud (LMC) galaxy. It finds that:
1) The proper motion data implies a stellar dynamical center that coincides with the HI dynamical center from previous studies.
2) Combining the proper motion and line-of-sight velocity data provides insights into the LMC's rotation curve, disk viewing angles, and circular rotation speed of 91.7 km/s outside the central region.
3) The data paint a consistent picture of LMC rotation and yield improved constraints on the galaxy's distance, mass profile, and orbital history around the Milky Way.
The green valley_is_a_red_herring_galaxy_zoo_reveals_two_evolutionary_pathwaysSérgio Sacani
This document summarizes research using data from Galaxy Zoo, SDSS, and GALEX to study how star formation is quenched in low-redshift galaxies. The key findings are:
1) Taking galaxy morphology into account, the "green valley" is not a single transitional state, as was previously thought.
2) Only a small population of blue early-type galaxies rapidly transition across the green valley as their morphology transforms from disk to spheroid and star formation is quenched quickly.
3) The majority of blue star-forming galaxies have significant disks and retain their late-type morphology as their star formation rates decline very slowly.
4) Different evolutionary pathways are observed for early- and late-type
Exploring the nature and synchronicity of early cluster formation in the Larg...Sérgio Sacani
We analyse Hubble Space Telescope observations of six globular clusters in the Large Magel- lanic Cloud (LMC) from programme GO-14164 in Cycle 23. These are the deepest available observations of the LMC globular cluster population; their uniformity facilitates a precise comparison with globular clusters in the Milky Way. Measuring the magnitude of the main- sequence turn-off point relative to template Galactic globular clusters allows the relative ages of the clusters to be determined with a mean precision of 8.4 per cent, and down to 6 per cent for individual objects. We find that the mean age of our LMC cluster ensemble is identical to the mean age of the oldest metal-poor clusters in the Milky Way halo to 0.2 ± 0.4 Gyr. This provides the most sensitive test to date of the synchronicity of the earliest epoch of globular cluster formation in two independent galaxies. Horizontal branch magnitudes and subdwarf fitting to the main sequence allow us to determine distance estimates for each cluster and examine their geometric distribution in the LMC. Using two different methods, we find an average distance to the LMC of 18.52 ± 0.05.
Fizzy Super-Earths: Impacts of Magma Composition on the Bulk Density and Stru...Sérgio Sacani
Lava worlds are a potential emerging population of Super-Earths that are on close-in orbits around their host stars,
with likely partially molten mantles. To date, few studies have addressed the impact of magma on the observed
properties of a planet. At ambient conditions, magma is less dense than solid rock; however, it is also more
compressible with increasing pressure. Therefore, it is unclear how large-scale magma oceans affect planet
observables, such as bulk density. We update ExoPlex, a thermodynamically self-consistent planet interior
software, to include anhydrous, hydrous (2.2 wt% H2O), and carbonated magmas (5.2 wt% CO2). We find that
Earth-like planets with magma oceans larger than ∼1.5 R⊕ and ∼3.2 M⊕ are modestly denser than an equivalentmass
solid planet. From our model, three classes of mantle structures emerge for magma ocean planets: (1) a
mantle magma ocean, (2) a surface magma ocean, and (3) one consisting of a surface magma ocean, a solid rock
layer, and a basal magma ocean. The class of planets in which a basal magma ocean is present may sequester
dissolved volatiles on billion-year timescales, in which a 4 M⊕ mass planet can trap more than 130 times the mass
of water than in Earth’s present-day oceans and 1000 times the carbon in the Earth’s surface and crust.
An interacting binary_system_powers_precessing_outflows_of_an_evolved_starSérgio Sacani
1) The authors discovered that the central star system in the planetary nebula Fleming 1 is a binary system with an orbital period of 1.1953 days.
2) They determine that the binary likely consists of a white dwarf primary star with a mass of 0.56-0.7 solar masses and a hotter white dwarf secondary star with a temperature over 120,000 K that provides the ionizing photons to power the nebula.
3) The discovery confirms that binary interactions can explain the precessing outflows and point-symmetric structures seen in Fleming 1 and other planetary nebulae with similar features.
The fornax deep_survey_with_vst_i_the_extended_and_diffuse_stellar_halo_of_ng...Sérgio Sacani
We have started a new deep, multi-imaging survey of the Fornax cluster, dubbed Fornax Deep
Survey (FDS), at the VLT Survey Telescope. In this paper we present the deep photometry inside
two square degrees around the bright galaxy NGC 1399 in the core of the cluster. We found that
the core of the Fornax cluster is characterised by a very extended and diffuse envelope surrounding
the luminous galaxy NGC 1399: we map the surface brightness out to 33 arcmin (∼ 192 kpc)
from the galaxy center and down to μg ∼ 31 mag arcsec−2 in the g band. The deep photometry
allows us to detect a faint stellar bridge in the intracluster region on the west side of NGC 1399
and towards NGC 1387. By analyzing the integrated colors of this feature, we argue that it
could be due to the ongoing interaction between the two galaxies, where the outer envelope of
NGC 1387 on its east side is stripped away. By fitting the light profile, we found that exists a
physical break radius in the total light distribution at R = 10 arcmin (∼ 58 kpc) that sets the
transition region between the bright central galaxy and the outer exponential halo, and that the
stellar halo contributes for 60% of the total light of the galaxy (Sec. 3.5). We discuss the main
implications of this work on the build-up of the stellar halo at the center of the Fornax cluster.
By comparing with the numerical simulations of the stellar halo formation for the most massive
BCGs (i.e. 13 < logM200/M⊙ < 14), we find that the observed stellar halo mass fraction is
consistent with a halo formed through the multiple accretion of progenitors with stellar mass in
the range 108 − 1011 M⊙. This might suggest that the halo of NGC 1399 has also gone through
a major merging event. The absence of a significant number of luminous stellar streams and
tidal tails out to 192 kpc suggests that the epoch of this strong interaction goes back to an early
formation epoch. Therefore, differently from the Virgo cluster, the extended stellar halo around
NGC 1399 is characterised by a more diffuse and well-mixed component, including the ICL.
The binding of cosmological structures by massless topological defectsSérgio Sacani
Assuming spherical symmetry and weak field, it is shown that if one solves the Poisson equation or the Einstein field
equations sourced by a topological defect, i.e. a singularity of a very specific form, the result is a localized gravitational
field capable of driving flat rotation (i.e. Keplerian circular orbits at a constant speed for all radii) of test masses on a thin
spherical shell without any underlying mass. Moreover, a large-scale structure which exploits this solution by assembling
concentrically a number of such topological defects can establish a flat stellar or galactic rotation curve, and can also deflect
light in the same manner as an equipotential (isothermal) sphere. Thus, the need for dark matter or modified gravity theory is
mitigated, at least in part.
EWOCS-I: The catalog of X-ray sources in Westerlund 1 from the Extended Weste...Sérgio Sacani
Context. With a mass exceeding several 104 M⊙ and a rich and dense population of massive stars, supermassive young star clusters
represent the most massive star-forming environment that is dominated by the feedback from massive stars and gravitational interactions
among stars.
Aims. In this paper we present the Extended Westerlund 1 and 2 Open Clusters Survey (EWOCS) project, which aims to investigate
the influence of the starburst environment on the formation of stars and planets, and on the evolution of both low and high mass stars.
The primary targets of this project are Westerlund 1 and 2, the closest supermassive star clusters to the Sun.
Methods. The project is based primarily on recent observations conducted with the Chandra and JWST observatories. Specifically,
the Chandra survey of Westerlund 1 consists of 36 new ACIS-I observations, nearly co-pointed, for a total exposure time of 1 Msec.
Additionally, we included 8 archival Chandra/ACIS-S observations. This paper presents the resulting catalog of X-ray sources within
and around Westerlund 1. Sources were detected by combining various existing methods, and photon extraction and source validation
were carried out using the ACIS-Extract software.
Results. The EWOCS X-ray catalog comprises 5963 validated sources out of the 9420 initially provided to ACIS-Extract, reaching a
photon flux threshold of approximately 2 × 10−8 photons cm−2
s
−1
. The X-ray sources exhibit a highly concentrated spatial distribution,
with 1075 sources located within the central 1 arcmin. We have successfully detected X-ray emissions from 126 out of the 166 known
massive stars of the cluster, and we have collected over 71 000 photons from the magnetar CXO J164710.20-455217.
More Related Content
Similar to Betelgeuse as a Merger of a Massive Star with a Companion
Kinematics and simulations_of_the_stellar_stream_in_the_halo_of_the_umbrella_...Sérgio Sacani
This document summarizes a study of the stellar stream and substructures around the Umbrella Galaxy (NGC 4651). Deep imaging and spectroscopy were used to characterize the properties and kinematics of the stream. Tracer objects like globular clusters and planetary nebulae were identified and found to delineate a kinematically cold feature in position-velocity space. Dynamical modeling suggests the stream originated from the tidal disruption of a dwarf galaxy on a highly eccentric orbit about 6-10 billion years ago. This work demonstrates the feasibility of using discrete tracers to recover the kinematics and model the dynamics of low surface brightness stellar streams around distant galaxies.
Detection of anisotropic satellite quenching in galaxy clusters up to z ∼ 1Sérgio Sacani
Satellite galaxies in the cluster environment are more likely to be quenched than galaxies in the general field. Recently, it has
been reported that satellite galaxy quenching depends on the orientation relative to their central galaxies: satellites along the
major axis of centrals are more likely to be quenched than those along the minor axis. In this paper, we report a detection
of such anisotropic quenching up to z ∼ 1 based on a large optically selected cluster catalogue constructed from the Hyper
Suprime-Cam Subaru Strategic Program. We calculate the quiescent satellite galaxy fraction as a function of orientation angle
measured from the major axis of central galaxies and find that the quiescent fractions at 0.25 < z < 1 are reasonably fitted
by sinusoidal functions with amplitudes of a few per cent. Anisotropy is clearer in inner regions (<r200m) of clusters and not
significant in cluster outskirts (>r200m). We also confirm that the observed anisotropy cannot be explained by differences in
local galaxy density or stellar mass distribution along the two axes. Quiescent fraction excesses between the two axes suggest
that the quenching efficiency contributing to the anisotropy is almost independent of stellar mass, at least down to our stellar
mass limit of M∗ = 1 × 1010 M. Finally, we argue that the physical origins of the observed anisotropy should have shorter
quenching time-scales than ∼ 1 Gyr, like ram-pressure stripping, because, for anisotropic quenching to be observed, satellites
must be quenched before their initial orientation angles are significantly changed.
HST imaging of star-forming clumps in 6 GASP ram-pressure stripped galaxiesSérgio Sacani
Exploiting broad- and narrow-band images of the Hubble Space Telescope from near-UV to I-band
restframe, we study the star-forming clumps of six galaxies of the GASP sample undergoing strong
ram-pressure stripping (RPS). Clumps are detected in Hα and near-UV, tracing star formation on
different timescales. We consider clumps located in galaxy disks, in the stripped tails and those
formed in stripped gas but still close to the disk, called extraplanar. We detect 2406 Hα-selected
clumps (1708 in disks, 375 in extraplanar regions, and 323 in tails) and 3750 UV-selected clumps (2026
disk clumps, 825 extraplanar clumps and 899 tail clumps). Only ∼ 15% of star-forming clumps are
spatially resolved, meaning that most are smaller than ∼ 140 pc. We study the luminosity and size
distribution functions (LDFs and SDFs, respectively) and the luminosity-size relation. The average
LDF slope is 1.79 ± 0.09, while the average SDF slope is 3.1 ± 0.5. Results suggest the star formation
to be turbulence driven and scale-free, as in main-sequence galaxies. All the clumps, whether they are
in the disks or in the tails, have an enhanced Hα luminosity at a given size, compared to the clumps in
main-sequence galaxies. Indeed, their Hα luminosity is closer to that of clumps in starburst galaxies,
indicating that ram pressure is able to enhance the luminosity. No striking differences are found among
disk and tail clumps, suggesting that the different environments in which they are embedded play a
minor role in influencing the star formation.
HST imaging of star-forming clumps in 6 GASP ram-pressure stripped galaxiesSérgio Sacani
Exploiting broad- and narrow-band images of the Hubble Space Telescope from near-UV to I-band
restframe, we study the star-forming clumps of six galaxies of the GASP sample undergoing strong
ram-pressure stripping (RPS). Clumps are detected in Hα and near-UV, tracing star formation on
different timescales. We consider clumps located in galaxy disks, in the stripped tails and those
formed in stripped gas but still close to the disk, called extraplanar. We detect 2406 Hα-selected
clumps (1708 in disks, 375 in extraplanar regions, and 323 in tails) and 3750 UV-selected clumps (2026
disk clumps, 825 extraplanar clumps and 899 tail clumps). Only ∼ 15% of star-forming clumps are
spatially resolved, meaning that most are smaller than ∼ 140 pc. We study the luminosity and size
distribution functions (LDFs and SDFs, respectively) and the luminosity-size relation. The average
LDF slope is 1.79 ± 0.09, while the average SDF slope is 3.1 ± 0.5. Results suggest the star formation
to be turbulence driven and scale-free, as in main-sequence galaxies. All the clumps, whether they are
in the disks or in the tails, have an enhanced Hα luminosity at a given size, compared to the clumps in
main-sequence galaxies. Indeed, their Hα luminosity is closer to that of clumps in starburst galaxies,
indicating that ram pressure is able to enhance the luminosity. No striking differences are found among
disk and tail clumps, suggesting that the different environments in which they are embedded play a
minor role in influencing the star formation.
HST imaging of star-forming clumps in 6 GASP ram-pressure stripped galaxiesSérgio Sacani
Exploiting broad- and narrow-band images of the Hubble Space Telescope from near-UV to I-band
restframe, we study the star-forming clumps of six galaxies of the GASP sample undergoing strong
ram-pressure stripping (RPS). Clumps are detected in Hα and near-UV, tracing star formation on
different timescales. We consider clumps located in galaxy disks, in the stripped tails and those
formed in stripped gas but still close to the disk, called extraplanar. We detect 2406 Hα-selected
clumps (1708 in disks, 375 in extraplanar regions, and 323 in tails) and 3750 UV-selected clumps (2026
disk clumps, 825 extraplanar clumps and 899 tail clumps). Only ∼ 15% of star-forming clumps are
spatially resolved, meaning that most are smaller than ∼ 140 pc. We study the luminosity and size
distribution functions (LDFs and SDFs, respectively) and the luminosity-size relation. The average
LDF slope is 1.79 ± 0.09, while the average SDF slope is 3.1 ± 0.5. Results suggest the star formation
to be turbulence driven and scale-free, as in main-sequence galaxies. All the clumps, whether they are
in the disks or in the tails, have an enhanced Hα luminosity at a given size, compared to the clumps in
main-sequence galaxies. Indeed, their Hα luminosity is closer to that of clumps in starburst galaxies,
indicating that ram pressure is able to enhance the luminosity. No striking differences are found among
disk and tail clumps, suggesting that the different environments in which they are embedded play a
minor role in influencing the star formation.
The pillars of_creation_revisited_with_muse_gas_kinematics_and_high_mass_stel...Sérgio Sacani
The document discusses observations of the Pillars of Creation in the Eagle Nebula using integral field spectroscopy from the MUSE instrument on the VLT. For the first time, the study maps physical parameters like extinction, density, temperature, and velocity across the pillars. The data show that the pillar tips have high densities and are being photoevaporated by the massive stars in NGC 6611. The kinematics indicate a blueshifted photoevaporative flow, consistent with simulations. The 3D geometry of the pillars is inferred, with some in front of and some behind the ionizing stars. A previously unknown outflow is detected from the middle pillar, suggesting an embedded protostar.
Is Betelgeuse Really Rotating? Synthetic ALMA Observations of Large-scale Con...Sérgio Sacani
The evolved stages of massive stars are poorly understood, but invaluable constraints can be derived from spatially resolved observations of nearby red supergiants, such as Betelgeuse. Atacama Large Millimeter/submillimeter Array (ALMA) observations of Betelgeuse showing a dipolar velocity field have been interpreted as evidence for a projected rotation rate of about 5 km s−1. This is 2 orders of magnitude larger than predicted by single-star evolution, which led to suggestions that Betelgeuse is a binary merger. We propose instead that large-scale convective motions can mimic rotation, especially if they are only partially resolved. We support this claim with 3D CO5BOLDsimulations of nonrotating red supergiants that we postprocessed to predict ALMA images and SiO spectra. We show that our synthetic radial velocity maps have a 90% chance of being falsely interpreted as evidence for a projected rotation rate of 2 km s−1 or larger for our fiducial simulation. We conclude that we need at least another ALMA observation to firmly establish whether Betelgeuse is indeed rapidly rotating. Such observations would also provide insight into the role of angular momentum and binary interaction in the late evolutionary stages. The data will further probe the structure and complex physical processes in the atmospheres of red supergiants, which are immediate progenitors of supernovae and are believed to be essential in the formation of gravitational-wave sources.
This study analyzed high-resolution spectra of 125 compact stellar systems (CSSs) in the giant elliptical galaxy NGC 5128 to measure their radial velocities and velocity dispersions. Combining these measurements with structural parameters from imaging, dynamical masses were derived for 112 CSSs, including 89 for the first time. Two distinct sequences were found in the dynamical mass-to-light ratio vs dynamical mass plane, which can be approximated by power laws. The shallower sequence corresponds to bright globular clusters, while the steeper relation appears to be populated by objects requiring significant dark matter such as central black holes or concentrated dark matter. This suggests different formation histories for these CSSs compared to classical globular clusters in NGC 5128 and
The Variable Detection of Atmospheric Escape around the Young, Hot Neptune AU...Sérgio Sacani
This document summarizes observations from the Hubble Space Telescope of the young hot Neptune exoplanet AU Mic b, which orbits the nearby M dwarf star AU Mic. The observations aimed to detect atmospheric escape of neutral hydrogen through absorption in the stellar Lyman-alpha emission line. Two visits were obtained, one in 2020 and one in 2021, corresponding to transits of the planet. A stellar flare was observed and removed from the first visit data. In the second visit, absorption was detected in the blue wing of the Lyman-alpha line 2.5 hours before the white light transit, indicating the presence of high-velocity neutral hydrogen escaping the planet's atmosphere and traveling toward the observer. Estimates place the column density of this material
Asymmetrical tidal tails of open star clusters: stars crossing their cluster’...Sérgio Sacani
The document discusses asymmetrical tidal tails observed around five open star clusters, which challenges Newtonian gravity. It summarizes how tidal tails form as stars escape clusters due to energy equipartition. Observations of the Hyades, Praesepe, Coma Berenices, COIN-Gaia 13, and NGC 752 clusters found more stars in the leading tidal tails within 50 pc of the clusters. Simulations show that in Newtonian gravity, tidal tails should be symmetrical, but asymmetries can arise in Milgromian dynamics. Future work is needed to better map tidal tails and develop Milgromian simulations.
UV and Hα HST observations of 6 GASP jellyfish galaxiesSérgio Sacani
Star-forming, Hα-emitting clumps are found embedded in the gaseous tails of galaxies undergoing
intense ram pressure stripping in galaxy clusters, so-called jellyfish galaxies. These clumps offer a
unique opportunity to study star formation under extreme conditions, in the absence of an underlying
disk and embedded within the hot intracluster medium. Yet, a comprehensive, high spatial resolution
study of these systems is missing. We obtained UVIS/HST data to observe the first statistical sample
of clumps in the tails and disks of six jellyfish galaxies from the GASP survey; we used a combination
of broad-band (UV to I) filters and a narrow-band Hα filter. HST observations are needed to study
the sizes, stellar masses and ages of the clumps and their clustering hierarchy. These observations will
be used to study the clump scaling relations, the universality of the star formation process and verify
whether a disk is irrelevant, as hinted by jellyfish galaxy results. This paper presents the observations,
data reduction strategy, and some general results based on the preliminary data analysis. The UVIS
high spatial resolution gives an unprecedented sharp view of the complex structure of the inner regions
of the galaxies and of the substructures in the galaxy disks. We found clear signatures of stripping
in regions very close in projection to the galactic disk. The star-forming regions in the stripped tails
are extremely bright and compact while we did not detect a significant number of star-forming clumps
outside those detected by MUSE. The paper finally presents the development plan for the project.
UV and Hα HST observations of 6 GASP jellyfish galaxiesSérgio Sacani
Star-forming, Hα-emitting clumps are found embedded in the gaseous tails of galaxies undergoing
intense ram pressure stripping in galaxy clusters, so-called jellyfish galaxies. These clumps offer a
unique opportunity to study star formation under extreme conditions, in the absence of an underlying
disk and embedded within the hot intracluster medium. Yet, a comprehensive, high spatial resolution
study of these systems is missing. We obtained UVIS/HST data to observe the first statistical sample
of clumps in the tails and disks of six jellyfish galaxies from the GASP survey; we used a combination
of broad-band (UV to I) filters and a narrow-band Hα filter. HST observations are needed to study
the sizes, stellar masses and ages of the clumps and their clustering hierarchy. These observations will
be used to study the clump scaling relations, the universality of the star formation process and verify
whether a disk is irrelevant, as hinted by jellyfish galaxy results. This paper presents the observations,
data reduction strategy, and some general results based on the preliminary data analysis. The UVIS
high spatial resolution gives an unprecedented sharp view of the complex structure of the inner regions
of the galaxies and of the substructures in the galaxy disks. We found clear signatures of stripping
in regions very close in projection to the galactic disk. The star-forming regions in the stripped tails
are extremely bright and compact while we did not detect a significant number of star-forming clumps
outside those detected by MUSE. The paper finally presents the development plan for the project.
UV and Hα HST observations of 6 GASP jellyfish galaxiesSérgio Sacani
Star-forming, Hα-emitting clumps are found embedded in the gaseous tails of galaxies undergoing
intense ram pressure stripping in galaxy clusters, so-called jellyfish galaxies. These clumps offer a
unique opportunity to study star formation under extreme conditions, in the absence of an underlying
disk and embedded within the hot intracluster medium. Yet, a comprehensive, high spatial resolution
study of these systems is missing. We obtained UVIS/HST data to observe the first statistical sample
of clumps in the tails and disks of six jellyfish galaxies from the GASP survey; we used a combination
of broad-band (UV to I) filters and a narrow-band Hα filter. HST observations are needed to study
the sizes, stellar masses and ages of the clumps and their clustering hierarchy. These observations will
be used to study the clump scaling relations, the universality of the star formation process and verify
whether a disk is irrelevant, as hinted by jellyfish galaxy results. This paper presents the observations,
data reduction strategy, and some general results based on the preliminary data analysis. The UVIS
high spatial resolution gives an unprecedented sharp view of the complex structure of the inner regions
of the galaxies and of the substructures in the galaxy disks. We found clear signatures of stripping
in regions very close in projection to the galactic disk. The star-forming regions in the stripped tails
are extremely bright and compact while we did not detect a significant number of star-forming clumps
outside those detected by MUSE. The paper finally presents the development plan for the project.
GRMHD Simulations of Neutron-star Mergers with Weak Interactions: r-process N...Sérgio Sacani
Fast neutron-rich material ejected dynamically over 10 ms during the merger of a binary neutron star (BNS) can
give rise to distinctive electromagnetic counterparts to the system’s gravitational-wave emission that serve as a
“smoking gun” to distinguish between a BNS and an NS–black hole merger. We present novel ab initio modeling
of the kilonova precursor and kilonova afterglow based on 3D general-relativistic magnetohydrodynamic
simulations of BNS mergers with nuclear, tabulated, finite-temperature equations of state (EOSs), weak
interactions, and approximate neutrino transport. We analyze dynamical mass ejection from 1.35–1.35 Me
binaries, consistent with properties of the first observed BNS merger GW170817, using three nuclear EOSs that
span the range of allowed compactness of 1.35 Me-neutron stars. Nuclear reaction network calculations yield a
robust second-to-third-peak r-process. We find few ×10−6 Me of fast (v > 0.6c) ejecta that give rise to broadband
synchrotron emission on ∼years timescales, consistent with tentative evidence for excess X-ray/radio emission
following GW170817. We find ≈2 × 10−5 Me of free neutrons that power a kilonova precursor on hours
timescale. A boost in early UV/optical brightness by a factor of a few due to previously neglected relativistic
effects, with enhancements up to 10 hr post-merger, is promising for future detection with UV/optical telescopes
like Swift or ULTRASAT. We find that a recently predicted opacity boost due to highly ionized lanthanides at
70,000 K is unlikely to affect the early kilonova based on the obtained ejecta structures. Azimuthal
inhomogeneities in dynamical ejecta composition for soft EOSs found here (“lanthanide/actinide pockets”) may
have observable consequences for both early kilonova and late-time nebular emission.
Third epoch magellanic_clouud_proper_motionsSérgio Sacani
The document analyzes proper motion data from the Hubble Space Telescope to study the three-dimensional rotation field of the Large Magellanic Cloud (LMC) galaxy. It finds that:
1) The proper motion data implies a stellar dynamical center that coincides with the HI dynamical center from previous studies.
2) Combining the proper motion and line-of-sight velocity data provides insights into the LMC's rotation curve, disk viewing angles, and circular rotation speed of 91.7 km/s outside the central region.
3) The data paint a consistent picture of LMC rotation and yield improved constraints on the galaxy's distance, mass profile, and orbital history around the Milky Way.
The green valley_is_a_red_herring_galaxy_zoo_reveals_two_evolutionary_pathwaysSérgio Sacani
This document summarizes research using data from Galaxy Zoo, SDSS, and GALEX to study how star formation is quenched in low-redshift galaxies. The key findings are:
1) Taking galaxy morphology into account, the "green valley" is not a single transitional state, as was previously thought.
2) Only a small population of blue early-type galaxies rapidly transition across the green valley as their morphology transforms from disk to spheroid and star formation is quenched quickly.
3) The majority of blue star-forming galaxies have significant disks and retain their late-type morphology as their star formation rates decline very slowly.
4) Different evolutionary pathways are observed for early- and late-type
Exploring the nature and synchronicity of early cluster formation in the Larg...Sérgio Sacani
We analyse Hubble Space Telescope observations of six globular clusters in the Large Magel- lanic Cloud (LMC) from programme GO-14164 in Cycle 23. These are the deepest available observations of the LMC globular cluster population; their uniformity facilitates a precise comparison with globular clusters in the Milky Way. Measuring the magnitude of the main- sequence turn-off point relative to template Galactic globular clusters allows the relative ages of the clusters to be determined with a mean precision of 8.4 per cent, and down to 6 per cent for individual objects. We find that the mean age of our LMC cluster ensemble is identical to the mean age of the oldest metal-poor clusters in the Milky Way halo to 0.2 ± 0.4 Gyr. This provides the most sensitive test to date of the synchronicity of the earliest epoch of globular cluster formation in two independent galaxies. Horizontal branch magnitudes and subdwarf fitting to the main sequence allow us to determine distance estimates for each cluster and examine their geometric distribution in the LMC. Using two different methods, we find an average distance to the LMC of 18.52 ± 0.05.
Fizzy Super-Earths: Impacts of Magma Composition on the Bulk Density and Stru...Sérgio Sacani
Lava worlds are a potential emerging population of Super-Earths that are on close-in orbits around their host stars,
with likely partially molten mantles. To date, few studies have addressed the impact of magma on the observed
properties of a planet. At ambient conditions, magma is less dense than solid rock; however, it is also more
compressible with increasing pressure. Therefore, it is unclear how large-scale magma oceans affect planet
observables, such as bulk density. We update ExoPlex, a thermodynamically self-consistent planet interior
software, to include anhydrous, hydrous (2.2 wt% H2O), and carbonated magmas (5.2 wt% CO2). We find that
Earth-like planets with magma oceans larger than ∼1.5 R⊕ and ∼3.2 M⊕ are modestly denser than an equivalentmass
solid planet. From our model, three classes of mantle structures emerge for magma ocean planets: (1) a
mantle magma ocean, (2) a surface magma ocean, and (3) one consisting of a surface magma ocean, a solid rock
layer, and a basal magma ocean. The class of planets in which a basal magma ocean is present may sequester
dissolved volatiles on billion-year timescales, in which a 4 M⊕ mass planet can trap more than 130 times the mass
of water than in Earth’s present-day oceans and 1000 times the carbon in the Earth’s surface and crust.
An interacting binary_system_powers_precessing_outflows_of_an_evolved_starSérgio Sacani
1) The authors discovered that the central star system in the planetary nebula Fleming 1 is a binary system with an orbital period of 1.1953 days.
2) They determine that the binary likely consists of a white dwarf primary star with a mass of 0.56-0.7 solar masses and a hotter white dwarf secondary star with a temperature over 120,000 K that provides the ionizing photons to power the nebula.
3) The discovery confirms that binary interactions can explain the precessing outflows and point-symmetric structures seen in Fleming 1 and other planetary nebulae with similar features.
The fornax deep_survey_with_vst_i_the_extended_and_diffuse_stellar_halo_of_ng...Sérgio Sacani
We have started a new deep, multi-imaging survey of the Fornax cluster, dubbed Fornax Deep
Survey (FDS), at the VLT Survey Telescope. In this paper we present the deep photometry inside
two square degrees around the bright galaxy NGC 1399 in the core of the cluster. We found that
the core of the Fornax cluster is characterised by a very extended and diffuse envelope surrounding
the luminous galaxy NGC 1399: we map the surface brightness out to 33 arcmin (∼ 192 kpc)
from the galaxy center and down to μg ∼ 31 mag arcsec−2 in the g band. The deep photometry
allows us to detect a faint stellar bridge in the intracluster region on the west side of NGC 1399
and towards NGC 1387. By analyzing the integrated colors of this feature, we argue that it
could be due to the ongoing interaction between the two galaxies, where the outer envelope of
NGC 1387 on its east side is stripped away. By fitting the light profile, we found that exists a
physical break radius in the total light distribution at R = 10 arcmin (∼ 58 kpc) that sets the
transition region between the bright central galaxy and the outer exponential halo, and that the
stellar halo contributes for 60% of the total light of the galaxy (Sec. 3.5). We discuss the main
implications of this work on the build-up of the stellar halo at the center of the Fornax cluster.
By comparing with the numerical simulations of the stellar halo formation for the most massive
BCGs (i.e. 13 < logM200/M⊙ < 14), we find that the observed stellar halo mass fraction is
consistent with a halo formed through the multiple accretion of progenitors with stellar mass in
the range 108 − 1011 M⊙. This might suggest that the halo of NGC 1399 has also gone through
a major merging event. The absence of a significant number of luminous stellar streams and
tidal tails out to 192 kpc suggests that the epoch of this strong interaction goes back to an early
formation epoch. Therefore, differently from the Virgo cluster, the extended stellar halo around
NGC 1399 is characterised by a more diffuse and well-mixed component, including the ICL.
Similar to Betelgeuse as a Merger of a Massive Star with a Companion (20)
The binding of cosmological structures by massless topological defectsSérgio Sacani
Assuming spherical symmetry and weak field, it is shown that if one solves the Poisson equation or the Einstein field
equations sourced by a topological defect, i.e. a singularity of a very specific form, the result is a localized gravitational
field capable of driving flat rotation (i.e. Keplerian circular orbits at a constant speed for all radii) of test masses on a thin
spherical shell without any underlying mass. Moreover, a large-scale structure which exploits this solution by assembling
concentrically a number of such topological defects can establish a flat stellar or galactic rotation curve, and can also deflect
light in the same manner as an equipotential (isothermal) sphere. Thus, the need for dark matter or modified gravity theory is
mitigated, at least in part.
EWOCS-I: The catalog of X-ray sources in Westerlund 1 from the Extended Weste...Sérgio Sacani
Context. With a mass exceeding several 104 M⊙ and a rich and dense population of massive stars, supermassive young star clusters
represent the most massive star-forming environment that is dominated by the feedback from massive stars and gravitational interactions
among stars.
Aims. In this paper we present the Extended Westerlund 1 and 2 Open Clusters Survey (EWOCS) project, which aims to investigate
the influence of the starburst environment on the formation of stars and planets, and on the evolution of both low and high mass stars.
The primary targets of this project are Westerlund 1 and 2, the closest supermassive star clusters to the Sun.
Methods. The project is based primarily on recent observations conducted with the Chandra and JWST observatories. Specifically,
the Chandra survey of Westerlund 1 consists of 36 new ACIS-I observations, nearly co-pointed, for a total exposure time of 1 Msec.
Additionally, we included 8 archival Chandra/ACIS-S observations. This paper presents the resulting catalog of X-ray sources within
and around Westerlund 1. Sources were detected by combining various existing methods, and photon extraction and source validation
were carried out using the ACIS-Extract software.
Results. The EWOCS X-ray catalog comprises 5963 validated sources out of the 9420 initially provided to ACIS-Extract, reaching a
photon flux threshold of approximately 2 × 10−8 photons cm−2
s
−1
. The X-ray sources exhibit a highly concentrated spatial distribution,
with 1075 sources located within the central 1 arcmin. We have successfully detected X-ray emissions from 126 out of the 166 known
massive stars of the cluster, and we have collected over 71 000 photons from the magnetar CXO J164710.20-455217.
The debris of the ‘last major merger’ is dynamically youngSérgio Sacani
The Milky Way’s (MW) inner stellar halo contains an [Fe/H]-rich component with highly eccentric orbits, often referred to as the
‘last major merger.’ Hypotheses for the origin of this component include Gaia-Sausage/Enceladus (GSE), where the progenitor
collided with the MW proto-disc 8–11 Gyr ago, and the Virgo Radial Merger (VRM), where the progenitor collided with the
MW disc within the last 3 Gyr. These two scenarios make different predictions about observable structure in local phase space,
because the morphology of debris depends on how long it has had to phase mix. The recently identified phase-space folds in Gaia
DR3 have positive caustic velocities, making them fundamentally different than the phase-mixed chevrons found in simulations
at late times. Roughly 20 per cent of the stars in the prograde local stellar halo are associated with the observed caustics. Based
on a simple phase-mixing model, the observed number of caustics are consistent with a merger that occurred 1–2 Gyr ago.
We also compare the observed phase-space distribution to FIRE-2 Latte simulations of GSE-like mergers, using a quantitative
measurement of phase mixing (2D causticality). The observed local phase-space distribution best matches the simulated data
1–2 Gyr after collision, and certainly not later than 3 Gyr. This is further evidence that the progenitor of the ‘last major merger’
did not collide with the MW proto-disc at early times, as is thought for the GSE, but instead collided with the MW disc within
the last few Gyr, consistent with the body of work surrounding the VRM.
Observation of Io’s Resurfacing via Plume Deposition Using Ground-based Adapt...Sérgio Sacani
Since volcanic activity was first discovered on Io from Voyager images in 1979, changes
on Io’s surface have been monitored from both spacecraft and ground-based telescopes.
Here, we present the highest spatial resolution images of Io ever obtained from a groundbased telescope. These images, acquired by the SHARK-VIS instrument on the Large
Binocular Telescope, show evidence of a major resurfacing event on Io’s trailing hemisphere. When compared to the most recent spacecraft images, the SHARK-VIS images
show that a plume deposit from a powerful eruption at Pillan Patera has covered part
of the long-lived Pele plume deposit. Although this type of resurfacing event may be common on Io, few have been detected due to the rarity of spacecraft visits and the previously low spatial resolution available from Earth-based telescopes. The SHARK-VIS instrument ushers in a new era of high resolution imaging of Io’s surface using adaptive
optics at visible wavelengths.
Earliest Galaxies in the JADES Origins Field: Luminosity Function and Cosmic ...Sérgio Sacani
We characterize the earliest galaxy population in the JADES Origins Field (JOF), the deepest
imaging field observed with JWST. We make use of the ancillary Hubble optical images (5 filters
spanning 0.4−0.9µm) and novel JWST images with 14 filters spanning 0.8−5µm, including 7 mediumband filters, and reaching total exposure times of up to 46 hours per filter. We combine all our data
at > 2.3µm to construct an ultradeep image, reaching as deep as ≈ 31.4 AB mag in the stack and
30.3-31.0 AB mag (5σ, r = 0.1” circular aperture) in individual filters. We measure photometric
redshifts and use robust selection criteria to identify a sample of eight galaxy candidates at redshifts
z = 11.5 − 15. These objects show compact half-light radii of R1/2 ∼ 50 − 200pc, stellar masses of
M⋆ ∼ 107−108M⊙, and star-formation rates of SFR ∼ 0.1−1 M⊙ yr−1
. Our search finds no candidates
at 15 < z < 20, placing upper limits at these redshifts. We develop a forward modeling approach to
infer the properties of the evolving luminosity function without binning in redshift or luminosity that
marginalizes over the photometric redshift uncertainty of our candidate galaxies and incorporates the
impact of non-detections. We find a z = 12 luminosity function in good agreement with prior results,
and that the luminosity function normalization and UV luminosity density decline by a factor of ∼ 2.5
from z = 12 to z = 14. We discuss the possible implications of our results in the context of theoretical
models for evolution of the dark matter halo mass function.
THE IMPORTANCE OF MARTIAN ATMOSPHERE SAMPLE RETURN.Sérgio Sacani
The return of a sample of near-surface atmosphere from Mars would facilitate answers to several first-order science questions surrounding the formation and evolution of the planet. One of the important aspects of terrestrial planet formation in general is the role that primary atmospheres played in influencing the chemistry and structure of the planets and their antecedents. Studies of the martian atmosphere can be used to investigate the role of a primary atmosphere in its history. Atmosphere samples would also inform our understanding of the near-surface chemistry of the planet, and ultimately the prospects for life. High-precision isotopic analyses of constituent gases are needed to address these questions, requiring that the analyses are made on returned samples rather than in situ.
Multi-source connectivity as the driver of solar wind variability in the heli...Sérgio Sacani
The ambient solar wind that flls the heliosphere originates from multiple
sources in the solar corona and is highly structured. It is often described
as high-speed, relatively homogeneous, plasma streams from coronal
holes and slow-speed, highly variable, streams whose source regions are
under debate. A key goal of ESA/NASA’s Solar Orbiter mission is to identify
solar wind sources and understand what drives the complexity seen in the
heliosphere. By combining magnetic feld modelling and spectroscopic
techniques with high-resolution observations and measurements, we show
that the solar wind variability detected in situ by Solar Orbiter in March
2022 is driven by spatio-temporal changes in the magnetic connectivity to
multiple sources in the solar atmosphere. The magnetic feld footpoints
connected to the spacecraft moved from the boundaries of a coronal hole
to one active region (12961) and then across to another region (12957). This
is refected in the in situ measurements, which show the transition from fast
to highly Alfvénic then to slow solar wind that is disrupted by the arrival of
a coronal mass ejection. Our results describe solar wind variability at 0.5 au
but are applicable to near-Earth observatories.
Gliese 12 b: A Temperate Earth-sized Planet at 12 pc Ideal for Atmospheric Tr...Sérgio Sacani
Recent discoveries of Earth-sized planets transiting nearby M dwarfs have made it possible to characterize the
atmospheres of terrestrial planets via follow-up spectroscopic observations. However, the number of such planets
receiving low insolation is still small, limiting our ability to understand the diversity of the atmospheric
composition and climates of temperate terrestrial planets. We report the discovery of an Earth-sized planet
transiting the nearby (12 pc) inactive M3.0 dwarf Gliese 12 (TOI-6251) with an orbital period (Porb) of 12.76 days.
The planet, Gliese 12 b, was initially identified as a candidate with an ambiguous Porb from TESS data. We
confirmed the transit signal and Porb using ground-based photometry with MuSCAT2 and MuSCAT3, and
validated the planetary nature of the signal using high-resolution images from Gemini/NIRI and Keck/NIRC2 as
well as radial velocity (RV) measurements from the InfraRed Doppler instrument on the Subaru 8.2 m telescope
and from CARMENES on the CAHA 3.5 m telescope. X-ray observations with XMM-Newton showed the host
star is inactive, with an X-ray-to-bolometric luminosity ratio of log 5.7 L L X bol » - . Joint analysis of the light
curves and RV measurements revealed that Gliese 12 b has a radius of 0.96 ± 0.05 R⊕,a3σ mass upper limit of
3.9 M⊕, and an equilibrium temperature of 315 ± 6 K assuming zero albedo. The transmission spectroscopy metric
(TSM) value of Gliese 12 b is close to the TSM values of the TRAPPIST-1 planets, adding Gliese 12 b to the small
list of potentially terrestrial, temperate planets amenable to atmospheric characterization with JWST.
Gliese 12 b, a temperate Earth-sized planet at 12 parsecs discovered with TES...Sérgio Sacani
We report on the discovery of Gliese 12 b, the nearest transiting temperate, Earth-sized planet found to date. Gliese 12 is a
bright (V = 12.6 mag, K = 7.8 mag) metal-poor M4V star only 12.162 ± 0.005 pc away from the Solar system with one of the
lowest stellar activity levels known for M-dwarfs. A planet candidate was detected by TESS based on only 3 transits in sectors
42, 43, and 57, with an ambiguity in the orbital period due to observational gaps. We performed follow-up transit observations
with CHEOPS and ground-based photometry with MINERVA-Australis, SPECULOOS, and Purple Mountain Observatory,
as well as further TESS observations in sector 70. We statistically validate Gliese 12 b as a planet with an orbital period of
12.76144 ± 0.00006 d and a radius of 1.0 ± 0.1 R⊕, resulting in an equilibrium temperature of ∼315 K. Gliese 12 b has excellent
future prospects for precise mass measurement, which may inform how planetary internal structure is affected by the stellar
compositional environment. Gliese 12 b also represents one of the best targets to study whether Earth-like planets orbiting cool
stars can retain their atmospheres, a crucial step to advance our understanding of habitability on Earth and across the galaxy.
The importance of continents, oceans and plate tectonics for the evolution of...Sérgio Sacani
Within the uncertainties of involved astronomical and biological parameters, the Drake Equation
typically predicts that there should be many exoplanets in our galaxy hosting active, communicative
civilizations (ACCs). These optimistic calculations are however not supported by evidence, which is
often referred to as the Fermi Paradox. Here, we elaborate on this long-standing enigma by showing
the importance of planetary tectonic style for biological evolution. We summarize growing evidence
that a prolonged transition from Mesoproterozoic active single lid tectonics (1.6 to 1.0 Ga) to modern
plate tectonics occurred in the Neoproterozoic Era (1.0 to 0.541 Ga), which dramatically accelerated
emergence and evolution of complex species. We further suggest that both continents and oceans
are required for ACCs because early evolution of simple life must happen in water but late evolution
of advanced life capable of creating technology must happen on land. We resolve the Fermi Paradox
(1) by adding two additional terms to the Drake Equation: foc
(the fraction of habitable exoplanets
with significant continents and oceans) and fpt
(the fraction of habitable exoplanets with significant
continents and oceans that have had plate tectonics operating for at least 0.5 Ga); and (2) by
demonstrating that the product of foc
and fpt
is very small (< 0.00003–0.002). We propose that the lack
of evidence for ACCs reflects the scarcity of long-lived plate tectonics and/or continents and oceans on
exoplanets with primitive life.
A Giant Impact Origin for the First Subduction on EarthSérgio Sacani
Hadean zircons provide a potential record of Earth's earliest subduction 4.3 billion years ago. Itremains enigmatic how subduction could be initiated so soon after the presumably Moon‐forming giant impact(MGI). Earlier studies found an increase in Earth's core‐mantle boundary (CMB) temperature due to theaccumulation of the impactor's core, and our recent work shows Earth's lower mantle remains largely solid, withsome of the impactor's mantle potentially surviving as the large low‐shear velocity provinces (LLSVPs). Here,we show that a hot post‐impact CMB drives the initiation of strong mantle plumes that can induce subductioninitiation ∼200 Myr after the MGI. 2D and 3D thermomechanical computations show that a high CMBtemperature is the primary factor triggering early subduction, with enrichment of heat‐producing elements inLLSVPs as another potential factor. The models link the earliest subduction to the MGI with implications forunderstanding the diverse tectonic regimes of rocky planets.
Climate extremes likely to drive land mammal extinction during next supercont...Sérgio Sacani
Mammals have dominated Earth for approximately 55 Myr thanks to their
adaptations and resilience to warming and cooling during the Cenozoic. All
life will eventually perish in a runaway greenhouse once absorbed solar
radiation exceeds the emission of thermal radiation in several billions of
years. However, conditions rendering the Earth naturally inhospitable to
mammals may develop sooner because of long-term processes linked to
plate tectonics (short-term perturbations are not considered here). In
~250 Myr, all continents will converge to form Earth’s next supercontinent,
Pangea Ultima. A natural consequence of the creation and decay of Pangea
Ultima will be extremes in pCO2 due to changes in volcanic rifting and
outgassing. Here we show that increased pCO2, solar energy (F⨀;
approximately +2.5% W m−2 greater than today) and continentality (larger
range in temperatures away from the ocean) lead to increasing warming
hostile to mammalian life. We assess their impact on mammalian
physiological limits (dry bulb, wet bulb and Humidex heat stress indicators)
as well as a planetary habitability index. Given mammals’ continued survival,
predicted background pCO2 levels of 410–816 ppm combined with increased
F⨀ will probably lead to a climate tipping point and their mass extinction.
The results also highlight how global landmass configuration, pCO2 and F⨀
play a critical role in planetary habitability.
Constraints on Neutrino Natal Kicks from Black-Hole Binary VFTS 243Sérgio Sacani
The recently reported observation of VFTS 243 is the first example of a massive black-hole binary
system with negligible binary interaction following black-hole formation. The black-hole mass (≈10M⊙)
and near-circular orbit (e ≈ 0.02) of VFTS 243 suggest that the progenitor star experienced complete
collapse, with energy-momentum being lost predominantly through neutrinos. VFTS 243 enables us to
constrain the natal kick and neutrino-emission asymmetry during black-hole formation. At 68% confidence
level, the natal kick velocity (mass decrement) is ≲10 km=s (≲1.0M⊙), with a full probability distribution
that peaks when ≈0.3M⊙ were ejected, presumably in neutrinos, and the black hole experienced a natal
kick of 4 km=s. The neutrino-emission asymmetry is ≲4%, with best fit values of ∼0–0.2%. Such a small
neutrino natal kick accompanying black-hole formation is in agreement with theoretical predictions.
Detectability of Solar Panels as a TechnosignatureSérgio Sacani
In this work, we assess the potential detectability of solar panels made of silicon on an Earth-like
exoplanet as a potential technosignature. Silicon-based photovoltaic cells have high reflectance in the
UV-VIS and in the near-IR, within the wavelength range of a space-based flagship mission concept
like the Habitable Worlds Observatory (HWO). Assuming that only solar energy is used to provide
the 2022 human energy needs with a land cover of ∼ 2.4%, and projecting the future energy demand
assuming various growth-rate scenarios, we assess the detectability with an 8 m HWO-like telescope.
Assuming the most favorable viewing orientation, and focusing on the strong absorption edge in the
ultraviolet-to-visible (0.34 − 0.52 µm), we find that several 100s of hours of observation time is needed
to reach a SNR of 5 for an Earth-like planet around a Sun-like star at 10pc, even with a solar panel
coverage of ∼ 23% land coverage of a future Earth. We discuss the necessity of concepts like Kardeshev
Type I/II civilizations and Dyson spheres, which would aim to harness vast amounts of energy. Even
with much larger populations than today, the total energy use of human civilization would be orders of
magnitude below the threshold for causing direct thermal heating or reaching the scale of a Kardashev
Type I civilization. Any extraterrrestrial civilization that likewise achieves sustainable population
levels may also find a limit on its need to expand, which suggests that a galaxy-spanning civilization
as imagined in the Fermi paradox may not exist.
Jet reorientation in central galaxies of clusters and groups: insights from V...Sérgio Sacani
Recent observations of galaxy clusters and groups with misalignments between their central AGN jets
and X-ray cavities, or with multiple misaligned cavities, have raised concerns about the jet – bubble
connection in cooling cores, and the processes responsible for jet realignment. To investigate the
frequency and causes of such misalignments, we construct a sample of 16 cool core galaxy clusters and
groups. Using VLBA radio data we measure the parsec-scale position angle of the jets, and compare
it with the position angle of the X-ray cavities detected in Chandra data. Using the overall sample
and selected subsets, we consistently find that there is a 30% – 38% chance to find a misalignment
larger than ∆Ψ = 45◦ when observing a cluster/group with a detected jet and at least one cavity. We
determine that projection may account for an apparently large ∆Ψ only in a fraction of objects (∼35%),
and given that gas dynamical disturbances (as sloshing) are found in both aligned and misaligned
systems, we exclude environmental perturbation as the main driver of cavity – jet misalignment.
Moreover, we find that large misalignments (up to ∼ 90◦
) are favored over smaller ones (45◦ ≤ ∆Ψ ≤
70◦
), and that the change in jet direction can occur on timescales between one and a few tens of Myr.
We conclude that misalignments are more likely related to actual reorientation of the jet axis, and we
discuss several engine-based mechanisms that may cause these dramatic changes.
The solar dynamo begins near the surfaceSérgio Sacani
The magnetic dynamo cycle of the Sun features a distinct pattern: a propagating
region of sunspot emergence appears around 30° latitude and vanishes near the
equator every 11 years (ref. 1). Moreover, longitudinal flows called torsional oscillations
closely shadow sunspot migration, undoubtedly sharing a common cause2. Contrary
to theories suggesting deep origins of these phenomena, helioseismology pinpoints
low-latitude torsional oscillations to the outer 5–10% of the Sun, the near-surface
shear layer3,4. Within this zone, inwardly increasing differential rotation coupled with
a poloidal magnetic field strongly implicates the magneto-rotational instability5,6,
prominent in accretion-disk theory and observed in laboratory experiments7.
Together, these two facts prompt the general question: whether the solar dynamo is
possibly a near-surface instability. Here we report strong affirmative evidence in stark
contrast to traditional models8 focusing on the deeper tachocline. Simple analytic
estimates show that the near-surface magneto-rotational instability better explains
the spatiotemporal scales of the torsional oscillations and inferred subsurface
magnetic field amplitudes9. State-of-the-art numerical simulations corroborate these
estimates and reproduce hemispherical magnetic current helicity laws10. The dynamo
resulting from a well-understood near-surface phenomenon improves prospects
for accurate predictions of full magnetic cycles and space weather, affecting the
electromagnetic infrastructure of Earth.
Exomoons & Exorings with the Habitable Worlds Observatory I: On the Detection...Sérgio Sacani
The highest priority recommendation of the Astro2020 Decadal Survey for space-based astronomy
was the construction of an observatory capable of characterizing habitable worlds. In this paper series
we explore the detectability of and interference from exomoons and exorings serendipitously observed
with the proposed Habitable Worlds Observatory (HWO) as it seeks to characterize exoplanets, starting
in this manuscript with Earth-Moon analog mutual events. Unlike transits, which only occur in systems
viewed near edge-on, shadow (i.e., solar eclipse) and lunar eclipse mutual events occur in almost every
star-planet-moon system. The cadence of these events can vary widely from ∼yearly to multiple events
per day, as was the case in our younger Earth-Moon system. Leveraging previous space-based (EPOXI)
lightcurves of a Moon transit and performance predictions from the LUVOIR-B concept, we derive
the detectability of Moon analogs with HWO. We determine that Earth-Moon analogs are detectable
with observation of ∼2-20 mutual events for systems within 10 pc, and larger moons should remain
detectable out to 20 pc. We explore the extent to which exomoon mutual events can mimic planet
features and weather. We find that HWO wavelength coverage in the near-IR, specifically in the 1.4 µm
water band where large moons can outshine their host planet, will aid in differentiating exomoon signals
from exoplanet variability. Finally, we predict that exomoons formed through collision processes akin
to our Moon are more likely to be detected in younger systems, where shorter orbital periods and
favorable geometry enhance the probability and frequency of mutual events.
Emergent ribozyme behaviors in oxychlorine brines indicate a unique niche for...Sérgio Sacani
Mars is a particularly attractive candidate among known astronomical objects
to potentially host life. Results from space exploration missions have provided
insights into Martian geochemistry that indicate oxychlorine species, particularly perchlorate, are ubiquitous features of the Martian geochemical landscape. Perchlorate presents potential obstacles for known forms of life due to
its toxicity. However, it can also provide potential benefits, such as producing
brines by deliquescence, like those thought to exist on present-day Mars. Here
we show perchlorate brines support folding and catalysis of functional RNAs,
while inactivating representative protein enzymes. Additionally, we show
perchlorate and other oxychlorine species enable ribozyme functions,
including homeostasis-like regulatory behavior and ribozyme-catalyzed
chlorination of organic molecules. We suggest nucleic acids are uniquely wellsuited to hypersaline Martian environments. Furthermore, Martian near- or
subsurface oxychlorine brines, and brines found in potential lifeforms, could
provide a unique niche for biomolecular evolution.
Continuum emission from within the plunging region of black hole discsSérgio Sacani
The thermal continuum emission observed from accreting black holes across X-ray bands has the potential to be leveraged as a
powerful probe of the mass and spin of the central black hole. The vast majority of existing ‘continuum fitting’ models neglect
emission sourced at and within the innermost stable circular orbit (ISCO) of the black hole. Numerical simulations, however,
find non-zero emission sourced from these regions. In this work, we extend existing techniques by including the emission
sourced from within the plunging region, utilizing new analytical models that reproduce the properties of numerical accretion
simulations. We show that in general the neglected intra-ISCO emission produces a hot-and-small quasi-blackbody component,
but can also produce a weak power-law tail for more extreme parameter regions. A similar hot-and-small blackbody component
has been added in by hand in an ad hoc manner to previous analyses of X-ray binary spectra. We show that the X-ray spectrum
of MAXI J1820+070 in a soft-state outburst is extremely well described by a full Kerr black hole disc, while conventional
models that neglect intra-ISCO emission are unable to reproduce the data. We believe this represents the first robust detection of
intra-ISCO emission in the literature, and allows additional constraints to be placed on the MAXI J1820 + 070 black hole spin
which must be low a• < 0.5 to allow a detectable intra-ISCO region. Emission from within the ISCO is the dominant emission
component in the MAXI J1820 + 070 spectrum between 6 and 10 keV, highlighting the necessity of including this region. Our
continuum fitting model is made publicly available.
WASP-69b’s Escaping Envelope Is Confined to a Tail Extending at Least 7 RpSérgio Sacani
Studying the escaping atmospheres of highly irradiated exoplanets is critical for understanding the physical
mechanisms that shape the demographics of close-in planets. A number of planetary outflows have been observed
as excess H/He absorption during/after transit. Such an outflow has been observed for WASP-69b by multiple
groups that disagree on the geometry and velocity structure of the outflow. Here, we report the detection of this
planet’s outflow using Keck/NIRSPEC for the first time. We observed the outflow 1.28 hr after egress until the
target set, demonstrating the outflow extends at least 5.8 × 105 km or 7.5 Rp This detection is significantly longer
than previous observations, which report an outflow extending ∼2.2 planet radii just 1 yr prior. The outflow is
blueshifted by −23 km s−1 in the planetary rest frame. We estimate a current mass-loss rate of 1 M⊕ Gyr−1
. Our
observations are most consistent with an outflow that is strongly sculpted by ram pressure from the stellar wind.
However, potential variability in the outflow could be due to time-varying interactions with the stellar wind or
differences in instrumental precision.
The use of Nauplii and metanauplii artemia in aquaculture (brine shrimp).pptxMAGOTI ERNEST
Although Artemia has been known to man for centuries, its use as a food for the culture of larval organisms apparently began only in the 1930s, when several investigators found that it made an excellent food for newly hatched fish larvae (Litvinenko et al., 2023). As aquaculture developed in the 1960s and ‘70s, the use of Artemia also became more widespread, due both to its convenience and to its nutritional value for larval organisms (Arenas-Pardo et al., 2024). The fact that Artemia dormant cysts can be stored for long periods in cans, and then used as an off-the-shelf food requiring only 24 h of incubation makes them the most convenient, least labor-intensive, live food available for aquaculture (Sorgeloos & Roubach, 2021). The nutritional value of Artemia, especially for marine organisms, is not constant, but varies both geographically and temporally. During the last decade, however, both the causes of Artemia nutritional variability and methods to improve poorquality Artemia have been identified (Loufi et al., 2024).
Brine shrimp (Artemia spp.) are used in marine aquaculture worldwide. Annually, more than 2,000 metric tons of dry cysts are used for cultivation of fish, crustacean, and shellfish larva. Brine shrimp are important to aquaculture because newly hatched brine shrimp nauplii (larvae) provide a food source for many fish fry (Mozanzadeh et al., 2021). Culture and harvesting of brine shrimp eggs represents another aspect of the aquaculture industry. Nauplii and metanauplii of Artemia, commonly known as brine shrimp, play a crucial role in aquaculture due to their nutritional value and suitability as live feed for many aquatic species, particularly in larval stages (Sorgeloos & Roubach, 2021).
Current Ms word generated power point presentation covers major details about the micronuclei test. It's significance and assays to conduct it. It is used to detect the micronuclei formation inside the cells of nearly every multicellular organism. It's formation takes place during chromosomal sepration at metaphase.
Or: Beyond linear.
Abstract: Equivariant neural networks are neural networks that incorporate symmetries. The nonlinear activation functions in these networks result in interesting nonlinear equivariant maps between simple representations, and motivate the key player of this talk: piecewise linear representation theory.
Disclaimer: No one is perfect, so please mind that there might be mistakes and typos.
dtubbenhauer@gmail.com
Corrected slides: dtubbenhauer.com/talks.html
The cost of acquiring information by natural selectionCarl Bergstrom
This is a short talk that I gave at the Banff International Research Station workshop on Modeling and Theory in Population Biology. The idea is to try to understand how the burden of natural selection relates to the amount of information that selection puts into the genome.
It's based on the first part of this research paper:
The cost of information acquisition by natural selection
Ryan Seamus McGee, Olivia Kosterlitz, Artem Kaznatcheev, Benjamin Kerr, Carl T. Bergstrom
bioRxiv 2022.07.02.498577; doi: https://doi.org/10.1101/2022.07.02.498577
Remote Sensing and Computational, Evolutionary, Supercomputing, and Intellige...University of Maribor
Slides from talk:
Aleš Zamuda: Remote Sensing and Computational, Evolutionary, Supercomputing, and Intelligent Systems.
11th International Conference on Electrical, Electronics and Computer Engineering (IcETRAN), Niš, 3-6 June 2024
Inter-Society Networking Panel GRSS/MTT-S/CIS Panel Session: Promoting Connection and Cooperation
https://www.etran.rs/2024/en/home-english/
ESPP presentation to EU Waste Water Network, 4th June 2024 “EU policies driving nutrient removal and recycling
and the revised UWWTD (Urban Waste Water Treatment Directive)”
ESR spectroscopy in liquid food and beverages.pptxPRIYANKA PATEL
With increasing population, people need to rely on packaged food stuffs. Packaging of food materials requires the preservation of food. There are various methods for the treatment of food to preserve them and irradiation treatment of food is one of them. It is the most common and the most harmless method for the food preservation as it does not alter the necessary micronutrients of food materials. Although irradiated food doesn’t cause any harm to the human health but still the quality assessment of food is required to provide consumers with necessary information about the food. ESR spectroscopy is the most sophisticated way to investigate the quality of the food and the free radicals induced during the processing of the food. ESR spin trapping technique is useful for the detection of highly unstable radicals in the food. The antioxidant capability of liquid food and beverages in mainly performed by spin trapping technique.
The technology uses reclaimed CO₂ as the dyeing medium in a closed loop process. When pressurized, CO₂ becomes supercritical (SC-CO₂). In this state CO₂ has a very high solvent power, allowing the dye to dissolve easily.
PPT on Direct Seeded Rice presented at the three-day 'Training and Validation Workshop on Modules of Climate Smart Agriculture (CSA) Technologies in South Asia' workshop on April 22, 2024.
mô tả các thí nghiệm về đánh giá tác động dòng khí hóa sau đốt
Betelgeuse as a Merger of a Massive Star with a Companion
1. Draft version October 24, 2023
Typeset using L
A
TEX twocolumn style in AASTeX631
Betelgeuse as a Merger of a Massive Star with a Companion
Sagiv Shiber,1
Emmanouil Chatzopoulos,1, 2
Bradley Munson,1
and Juhan Frank1
1Department of Physics and Astronomy, Louisiana State University, Baton Rouge, LA 70803, USA
2Institute of Astrophysics, Foundation for Research and Technology-Hellas (FORTH), Heraklion, 70013, Greece
ABSTRACT
We investigate the merger between a 16M⊙ star, on its way to becoming a red supergiant (RSG), and
a 4M⊙ main-sequence companion. Our study employs three-dimensional hydrodynamic simulations
using the state-of-the-art adaptive mesh refinement code Octo-Tiger. The initially corotating binary
undergoes interaction and mass transfer, resulting in the accumulation of mass around the companion
and its subsequent loss through the second Lagrangian point (L2). The companion eventually plunges
into the envelope of the primary, leading to its spin-up and subsequent merger with the helium core. We
examine the internal structural properties of the post-merger star, as well as the merger environment
and the outflow driven by the merger. Our findings reveal the ejection of approximately ∼ 0.6 M⊙ of
material in an asymmetric and somewhat bipolar outflow. We import the post-merger stellar structure
into the MESA stellar evolution code to model its long-term nuclear evolution. In certain cases, the
post-merger star exhibits persistent rapid equatorial surface rotation as it evolves in the H-R diagram
towards the observed location of Betelgeuse. These cases demonstrate surface rotation velocities of
a similar magnitude to those observed in Betelgeuse, along with a chemical composition resembling
that of Betelgeuse. In other cases, efficient rotationally-induced mixing leads to slower surface rotation.
This pioneering study aims to model stellar mergers across critical timescales, encompassing dynamical,
thermal, and nuclear evolutionary stages.
Keywords: binaries: close — stars: evolution — hydrodynamics — methods: numerical
1. INTRODUCTION
It has been firmly established that the majority of
massive stars exist within binary systems (Mason et al.
2009; Dunstall et al. 2015). Furthermore, a significant
portion of these systems undergo binary interactions at
some point during their evolution (Sana et al. 2012; de
Mink et al. 2013; Renzo et al. 2019). In extreme cases,
these interactions can result in the complete merging of
the two stars (Bonnell & Bate 2005; de Mink et al. 2014).
Depending on the initial conditions that trigger a stellar
merger, there can be various outcomes (Podsiadlowski
et al. 2006; Schneider et al. 2016). The merger event may
be accompanied by a short-lived, relatively faint electro-
magnetic transient referred to as a “merge-burst” (Soker
& Tylenda 2006), as well as mass loss occurring along
the orbital plane of the binary progenitor system (Bo-
Corresponding author: Sagiv Shiber
sshiber1@lsu.edu
denheimer & Taam 1984; Taam & Bodenheimer 1991;
Terman et al. 1994).
If the secondary star gets past the initial common-
envelope (CE) phase and spirals inward into the ex-
tended envelope of a primary star that is evolved past
the main–sequence (MS) with a helium (He) core, the
outcome will depend on which component has the high-
est central density. If mass transfer started in Case
B, when the primary had already developed a com-
pact core, the secondary may experience tidal disrup-
tion outside the core of the primary and subsequently
merge with it. If no hydrogen-rich material is mixed
into the primary core, we have what we may classify as
a Case B-quiet merger. The extent to which the dis-
rupted secondary material mixes with the core of the
primary, known as the penetration depth of the stream
(Ivanova et al. 2002; Ivanova & Podsiadlowski 2002),
determines whether there is sufficient fresh fuel to reju-
venate the nuclear evolution of the secondary star, lead-
ing to a new phase of core hydrogen burning (Ivanova
2002; Ivanova & Podsiadlowski 2003). Rejuvenated
arXiv:2310.14603v1
[astro-ph.SR]
23
Oct
2023
2. 2 Shiber et al.
post-merger stars are likely to evolve into compact, hot
blue supergiant (BSG) supernova (SN) progenitors, sim-
ilar to Sk – 69° 202, the progenitor of SN1987A (Menon
& Heger 2017; Menon et al. 2019). Recent studies have
demonstrated that the degree of core penetration and
rejuvenation of the primary star strongly depends on
the original binary mass ratio, denoted as q = M2/M1,
where M1 and M2 are the masses of the primary star
(initially the donor) and the secondary star (initially the
accretor) respectively. Mergers following Case B mass
transfer, in systems where q ≲ 0.25 tend to yield a quiet
merger and evolve towards the red supergiant (RSG)
phase (Podsiadlowski et al. 1990; Ivanova et al. 2002).
Even in the case of a Case B-quiet merger scenario,
the post-merger star’s evolution is unlikely to resemble
that of a single massive star. Depending on the initial
period (or binary separation) of the system when the
CE phase begins, the secondary star may deposit signif-
icant amounts of angular momentum into the envelope
of the primary star, resulting in spin-up and enhanced
rotation-induced chemical mixing (Wheeler et al. 2017).
These effects can give rise to a rapidly rotating RSG
with elevated surface nitrogen (14
N) abundances. While
a few observations of evolved, lower-mass red giant stars
support this notion (Costa et al. 2015), the most in-
triguing case is that of Betelgeuse (α Orionis), a mas-
sive, evolved RSG star exhibiting evidence of fast surface
equatorial rotation (Uitenbroek et al. 1998; Gilliland &
Dupree 1996; Wheeler & Chatzopoulos 2023). Recent
measurements from the Atacama Large Millimeter Ar-
ray (ALMA) indicate a surface equatorial rotational ve-
locity of 5–15 km s−1
for Betelgeuse (Kervella et al.
2018), while measurements of its surface abundances re-
veal nitrogen-to-carbon (N/C) and nitrogen-to-oxygen
(N/O) ratios of 2.9 and 0.6, respectively (Lambert et al.
1984) far in excess of standard solar values. Recent
theoretical work has shown that early Case B mergers
with mass ratio in the range 0.07 < q < 0.25, primary
mass 15–16M⊙, secondary masses 1–4 M⊙ where the
CE phase is triggered during the expansion of the pri-
mary to the RSG stage (the “Hertzsprung gap” crossing
phase), at primary radii 50–300 R⊙ can reproduce the
current observed state of Betelgeuse, indicating that a
past merger is a viable explanation for this extraordi-
nary star (Chatzopoulos et al. 2020).
While Chatzopoulos et al. (2020) present a compelling
argument for explaining some of the observed charac-
teristics of Betelgeuse, their approach is constrained by
several simplifying assumptions that rely on basic ap-
proaches, including a spherically-symmetric 1D treat-
ment and an analytical expression for the specific an-
gular momentum deposition into the envelope of the
primary star. These assumptions assume that the struc-
ture of the secondary star remains unaffected during the
common-envelope (CE) in-spiral phase and that the in–
spiral time-scale of the secondary is significantly shorter
than the thermal adjustment time–scale of the primary’s
envelope. Additionally, there is some disagreement re-
garding whether the high measured rotational velocity
of Betelgeuse reflects actual surface rotation or other
phenomena, such as large-scale convective plume mo-
tion (López Ariste et al. 2018; Jadlovský et al. 2023).
Furthermore, certain properties of the star, such as the
enhanced surface abundance of 14
N, remain puzzling
within the context of the evolution of single massive
stars.
The objective of this research is to comprehensively
and consistently investigate the merger scenario for
Betelgeuse and, more broadly, rapidly–spinning red su-
pergiant (RSG) stars, using three-dimensional (3D) hy-
drodynamics merger simulations. In particular, we make
use of the updated and bench-marked 3D adaptive mesh
refinement (AMR) Octo-Tiger (Kadam et al. 2018;
Marcello et al. 2021) code to model the CE in–spiral
and final secondary–primary core merger of a q = 0.25,
16 M⊙ primary right after the end of its core H–burning
phase and expanded at a radius of ∼ 50 R⊙ with a 4 M⊙
main–sequence (MS) secondary. Additionally, we track
the 3D evolution of the post–merger star for several or-
bits after the merger to obtain a realistic structure of
the post–merger star, including the distribution of its
internal angular momentum. We also monitor the ex-
pansion of dynamically unbound mass loss caused by the
merger. The resulting 3D post–merger structure is then
spherically averaged and incorporated into the 1D stel-
lar evolution code known as Modules for Experiments in
Stellar Astrophysics (MESA; Paxton et al. 2011, 2013,
2015, 2018, 2019). This integration enables us to explore
the long-term nuclear evolution of the post-merger star
until it reaches the RSG phase and compare our findings
with observations of Betelgeuse.
To the best of our knowledge, this is the first study
in the literature that self–consistently simulates the 3D
dynamics of the CE and merger phase, as well as the
long–term nuclear evolution of the post–merger star in
1D. Given the extensive simulation box used to track
the expansion of the mass loss induced by the merger,
and the high resolution required to accurately depict the
structure of the secondary star and ensure its structural
stability, this simulation is the first in its kind. It took
nearly an entire calendar year to complete and involved
multiple successive compute time allocations. The in-
vestment of time was justified, as we were able to con-
firm that, under certain conditions, “quiet” high mass-
3. Betelgeuse as a merger 3
ratio mergers of this nature can indeed produce RSGs
with properties similar to those observed in Betelgeuse.
Moreover, the significant mass loss that can occur dur-
ing the merger process can lead to non-spherically sym-
metric circumstellar (CS) environments with properties
and geometries reminiscent of those observed in other
systems, such as SN1987A (Plait et al. 1995).
In Section 2, we provide a comprehensive description
of our numerical setup and the initial conditions of the
binary system in detail. Subsequently, in Section 3, we
concisely outline the outcomes derived from our three-
dimensional (3D) dynamical merger simulations employ-
ing the Octo-Tiger model, as well as the long-term
nuclear evolution simulations conducted in one dimen-
sion (1D) using the MESA code. Lastly, in Section 4,
we succinctly summarize the findings of our study and
engage in a thorough discussion of the principal conclu-
sions drawn, along with their implications for the evo-
lution of massive stars following a merger event.
2. NUMERICAL SET-UP
Our primary and secondary models are constructed
based on one-dimensional profiles that were simultane-
ously evolved using the MESA stellar evolution code
from the Zero Age Main Sequence (ZAMS). The primary
star originates with a ZAMS mass of 16M⊙, while the
secondary star begins with a ZAMS mass of 4M⊙. These
masses align with the q = 0.25 binary mergers examined
in Chatzopoulos et al. (2020), which have been identi-
fied as fitting Betelgeuse’s inferred surface rotation with
surface velocities ranging from 4 − 12 km/sec. These
velocities persist for time spans of 7 − 8 × 105
yr. Both
stellar models were initialized assuming solar metallicity
and utilized standard mass-loss prescriptions appropri-
ate for their respective masses and evolutionary phases
(de Jager et al. 1988; Vink et al. 2001).
Following the methodology employed in Chatzopou-
los et al. (2020), our models were terminated after the
primary star completed its evolution off the main se-
quence and traversed the Hertzsprung gap (HG) phase.
During this transitional stage, the primary’s envelope
expands on a thermal time scale, progressing towards
the RSG state. The primary star reaches a radius of
R1 = 50R⊙, which is smaller in comparison to the pri-
mary radius ranges investigated in Chatzopoulos et al.
(2020) (typically > 200R⊙). This deliberate choice was
made to minimize computational time, as a larger enve-
lope would result in longer dynamical timescales (pro-
portional to ∼ R3/2
) and require a higher cell count
for adequate resolution. At this stage, the age of the
binary system is 1.11 × 107
yr, and the primary star’s
mass has decreased to M1 = 15.48M⊙ due to wind-
driven mass loss. The primary star exhibits a luminos-
ity of L1 = 55, 000L⊙ and an effective temperature of
Teff,1 = 12, 600 K. The secondary star, on the other
hand, remains in the main sequence phase at this age,
with a radius of R2 = 2.43 R⊙.
To incorporate the MESA structures into Octo-
Tiger’s grid, we first approximate the internal struc-
tures of the two stars by fitting them to single poly-
tropes. We determine that polytropic indices of n1 = 4.1
and n2 = 3.4 provide the best fit for the primary star
(referred to as star 1) and the secondary star (referred to
as star 2) respectively. Subsequently, we utilize Octo-
Tiger’s self-consistent field (SCF) technique (Kadam
et al. 2018) to construct an equilibrium binary system
with synchronous rotation. The SCF method initializes
each star as a polytrope and iterates until the desired
level of equilibrium is attained (for further details, re-
fer to Marcello et al. 2021). The level of equilibrium is
quantified by deviations from the virial relation. Specifi-
cally, the SCF produces models in which the virial error,
defined as VE = |(2Ek + Eg + 2Ei) /Eg|, is as small as
10−3
. Here Ek, Eg, and Ei, are the total kinetic, grav-
itational and internal (thermal) energies of the binary,
respectively. The SCF process ensures the conservation
of mass for each star, the ratio of core mass to the to-
tal star mass (particularly relevant in cases where there
is a difference in mean molecular weight or composition
between the core and the envelope, as seen in star 1), as
well as the initial Roche Lobe (RL) filling factor. Addi-
tionally, the structures generated by the SCF technique
incorporate the effects of tidal distortion and rotational
flattening of the stars as intentional design features.
In our simulation, we assign the masses to be identi-
cal to those specified in the original MESA 1D profiles.
Additionally, we opt for a RL filling factor of 1, indi-
cating that the primary star precisely occupies its RL.
These choices establish the initial separation at 99.6R⊙.
Furthermore, to thoroughly investigate the structure,
kinematics, and energetics of merger-driven outflows, we
utilize an expansive simulation box with dimensions ap-
proximately 40 times the initial orbital separation, re-
sulting in a box size of (4000R⊙)
3
.
Our AMR grid has 10 levels of refinement that are
controlled by a density refinement criterion, and two ex-
tra refinement levels for the secondary star. These two
extra refinements are done by exploiting Octo-Tiger’s
ability to define different species, which we use to differ-
entiate between primary and secondary star densities.
Specifically, we refine by two extra levels cells in which
the secondary mass fraction exceeds the value of half.
The two extra refinement levels are required for the cor-
rect computation of the gravitational force onto the sec-
4. 4 Shiber et al.
ondary star’s cells (see subsection 2.2 for more details).
This yields a minimal cell size of (∆x)primary
min = 0.49 R⊙
and (∆x)secondary
min = 0.12 R⊙, for the primary and sec-
ondary stars, respectively.
In Figure 1 we show the initial density (left) and pres-
sure (right) maps of the binary that were produced by
the SCF. We plot density and pressure at the equatorial
plane. The right panel also illustrates the adaptive mesh
in our simulation (gray and black squares). Each such a
square represents a subgrid consisting of 83
= 512 cells.
We resolve ∼ 200 cells across the primary star’s diam-
eter (along the x axis), and ∼ 70 across the secondary
star’s diameter. The left panel presents contours of ef-
fective potential which is the sum of the gravitational
and rotational potentials, demonstrating the teardrop
shape of the primary star occupying its RL. The overall
initial cell count in the grid is 6.6 × 106
.
During the SCF iterations, a polytropic equation of
state (EoS) is assumed, with each star having a differ-
ent polytropic index. However, once the simulation en-
ters the evolution phase after initialization, an ideal gas
equation of state is utilized. Radiation pressure is dis-
regarded, and the temperature is calculated using the
ideal gas law, taking into consideration the mean molec-
ular weight of each cell. This approach may result in an
overestimation of the temperature, as the inclusion of
radiation pressure in the EoS would have likely resulted
in lower temperatures. In the future, a revised version
of Octo-Tiger will be employed, incorporating a more
comprehensive stellar equation of state (EoS) to effec-
tively address temperature inconsistencies.
It is crucial to emphasize that Octo-Tiger handles
the evolution of inertial frame quantities within a rotat-
ing grid (for a detailed and comprehensive code descrip-
tion, refer to Marcello et al. 2021). This implementation
involves a grid that constantly rotates at the same fre-
quency as the initial binary frequency. In the rotating
frame, the stars begin without initial velocities, while
the dilute gas surrounding the stars does possess veloc-
ities. This deliberate approach significantly diminishes
the impact of viscosity effects that could potentially hin-
der the accurate progression of the binary system.
The upcoming two subsections focus on individual ex-
aminations of the initial structures and dynamical sta-
bility of each star. It is demonstrated that, despite in-
herent limitations in resolution and computational re-
sources, we successfully replicate the structure of both
stars with a commendable level of accuracy. Notably,
our simulations closely replicate the primary star’s en-
velope as per the original MESA structure. This enables
us to investigate the impact of envelope spin-up, which
stands as a significant objective of this study.
2.1. Primary star’s structure and stability
As previously mentioned, our primary star initi-
ates the Octo-Tiger binary simulation with a mass
of 15.48M⊙. Leveraging Octo-Tiger’s capability to
track different species, we initialize the primary star
with two distinct species: one for the core and one for
the envelope. To determine the core mass, we locate the
mass coordinate in the MESA model where the abun-
dance of Helium falls below that of Hydrogen, which
corresponds to M1,core = 6.04M⊙. Subsequently, we set
the molecular weight of the core to the average molecular
weight computed over the mass coordinate m ≤ M1,core,
resulting in µ1,core = 1.21. For the envelope, we calcu-
late the average molecular weight over the mass coordi-
nate m > M1,core, yielding µ1,env = 0.63. It is impor-
tant to note that various definitions exist for the core
of a star. However, we adopt a definition that primar-
ily captures the characteristics of the envelope rather
than the core, as our primary focus lies in investigating
the envelope of the primary star and its acquisition of
angular momentum through the merger process.
In Figure 2 we compare the primary’s structure in
Octo-Tiger (thick lines) with the MESA model (thin
lines). This figure is similar to Figure 1 of Lau et al.
(2022a), where they plot composition (dashed and dash-
dotted lines) and density (blue solid lines) as a function
of mass coordinate, but we also plot the initial compo-
sition of our 3D model as well as the radius vs mass
coordinates (red dotted lines).
The density and composition in our simulation align
well with the MESA values in the outermost 5 solar
masses of the star. There is also a good agreement in
an intermediate region spanning from 6M⊙ to 10M⊙.
However, due to our approximation of the star as a
polytrope, we face a limitation in resolving the high-
density regions near the core. This limitation arises
from numerical constraints and the considerable com-
putational cost associated with our 3D simulation. The
dense and compact core cannot be adequately resolved
without encountering small time steps that would ren-
der the merger simulation unfeasible within a reasonable
timeframe. Consequently, in Octo-Tiger, the “core”
extends to approximately 5 R⊙, which is approximately
2.7 times larger than the core in the MESA model. In
alternative studies (such as in Lau et al. 2022a), the
dense core is replaced with a point particle to circum-
vent these challenges. However, the use of a point par-
ticle introduces a softening length that may influence
the evolution when the secondary star approaches the
core particle closely, and it remains uncertain whether
a merger could occur under such circumstances. Never-
theless, ongoing work is being conducted to implement
5. Betelgeuse as a merger 5
0.4 0.20.0 0.2 0.4
x [AU]
0.4
0.2
0.0
0.2
0.4
y
[AU]
0.0
0.4 0.20.0 0.2 0.4
x [AU]
0.0
10 11
10 9
10 7
10 5
10 3
10 1
101
Density
(
g
cm
3
)
10 1
101
103
105
107
109
1011
1013
Pressure
(
erg
cm
3
)
Figure 1. Density (left) and pressure (right) slices at the equatorial plane at t = 0 of our Octo-Tiger simulation. The right
panel also shows the AMR grid and the extra refinement placed on the secondary star. The left panel also presents contours of
effective potential (gravitational plus rotational). Both panels zoom-in on the central 1 AU of the grid, (∼ 1/20 of the simulation
domain size)
0 10
m [M ]
10−10
10−6
10−2
102
10−10
10−8
10−6
10−4
10−2
100
102
ρ[g/cm
3
]
/
r/R
ρ
r/R
0.00
0.25
0.50
0.75
1.00
X
i
1
H
4
He
Figure 2. Comparison of the primary star structure when
imported to the 3D grid (thick lines) with the original MESA
model (thin lines). Density (blue solid lines), radius (red dot-
ted lines), Hydrogen mass fraction (orange dashed lines), and
Helium mass fraction (green dashed-dotted lines) are plotted
as a function of the mass coordinate m. The adequate rep-
resentation of the envelope (m = 6 − 15.5 M⊙) enables us to
study the post-merger spin-up and envelope composition
point particle treatment within the Octo-Tiger code,
which will be beneficial for future investigations. In
summary, the structure of our primary star adequately
represents the corresponding MESA structure in the re-
gions of primary interest for this study. This enables us
to examine the post-merger spin-up and envelope com-
position. Figure 3 illustrates the comparison between
our simulation and the MESA model, depicting the ini-
tial primary star’s density (left), pressure (center), and
temperature (right) as functions of radius. Because the
primary star fills its RL, it has a teardrop shape and is
more extended towards the binary axis, xBinary. There-
fore we show three line-plots in each panel: along the line
that go from the center of the primary to the direction of
the secondary star center (∥ xbinary; blue circles), in per-
pendicular to this binary axis (⊥xbinary; orange x’s) as
well as mass averaged profile (’Avg.’; green pentagons).
The figure demonstrates a close match between the two
models in most spatial regions.
In order to assess the stability of the primary star,
we conducted single star simulations using polytropic
models with an index of n = 4.1. Our investigations re-
vealed that resolution plays a crucial role in maintaining
stability, and we determined that a minimum resolution
of 128 cells across the diameter of the primary star is
necessary to ensure stability over an extended period
(see Appendix A for further details). At this resolution,
the star experiences only a slight collapse after approx-
imately 140 dynamical orbits. Although this collapse
may potentially reduce mass transfer during the binary
simulation and consequently prolong the time to merger,
we mitigate this effect by employing a higher resolution
in the binary simulation. In fact, we use 3/2 more cells
across the diameter of the primary star in the binary
simulation, thereby minimizing the impact of this minor
collapse and maintaining the star’s stability throughout
the binary evolution.
Furthermore, due to the limited lifetime of a star with
coarser grid resolution, it is not feasible to run a binary
simulation using a coarser grid as the star would collapse
6. 6 Shiber et al.
0 20 40
Radius [R ]
10−7
10−3
101
Density
[g/cm
3
]
k xBinary
⊥xBinary
Avg.
MESA
0 20 40
Radius [R ]
106
1011
1016
Pressure
[erg/cm
3
]
k xBinary
⊥xBinary
Avg.
MESA
0 20 40
Radius [R ]
105
107
104
105
106
107
108
Temperature
[K]
k xBinary
⊥xBinary
Avg.
MESA
Figure 3. Density (left), pressure, (center), and temperature (right) as a function of radius of the initial primary star in our
simulation. As the primary star fills its Roche Lobe, it is not completely spherically symmetric, and we therefore show lines that
goes along the binary axis, xBinary (lines that go from the center of the primary to the direction of the secondary star center;
blue circles), and in perpendicular to the binary axis (orange x’s) as well as mass averaged profiles (green pentagons). We also
plot the 1D MESA profile (solid red line), showing again that the envelope structure in our simulation is well matched to the
MESA model
before the merger could take place. Conversely, a finer
grid simulation would incur a prohibitively high compu-
tational cost. Consequently, we were unable to conduct
a comprehensive resolution study for the specific binary
merger simulation presented in this paper.
2.2. Secondary star’s structure
In accordance with the SCF technique, the size of
the secondary star is determined by its RL filling fac-
tor. However, it is important to note that the resolution
around the secondary star can impact its size and the
SCF may not converge for certain small filling factor
values if the resolution is insufficient. Insufficient reso-
lution around the secondary star can also lead to signif-
icant fluctuations in the calculated gravitational forces,
which can greatly hinder the conservation of angular
momentum, and can cause the stars to wiggle around
the center of mass. To address this issue, we apply
two additional refinement levels around the secondary
star. Additionally, we select the smallest filling factor
that still converges at this resolution. In Figure 4 we
plot density (left), pressure (center), and temperature
(right) as a function of radius of the resulted secondary
star structure and we compare it to the MESA
model.
The secondary star obtained by the SCF is larger than
the corresponding MESA model but remains within a
reasonable range for a main sequence star. Increasing
the resolution around the secondary star could have re-
sulted in a smaller star size. However, it would also
slow-down the calculation by at least a factor two, caus-
ing the simulation to become too expensive to run. Since
the drag force depends on the accretion radius, it will
not be affected by the actual size of the secondary star
unless the orbital separation becomes very small. How-
ever, by that stage, ablation may have already changed
the effective size of the secondary star. Nonetheless, a
smaller star might accrete less mass and more artificial
driving by extraction of angular momentum would be
required for the dynamical plunge-in to occur. Overall,
resolving the secondary star is already an improvement
from previous studies which utilize the secondary star as
a point-particle that does not have an actual size (except
maybe a numerical size like a softening length).
While the secondary star’s central density is slightly
smaller than in the MESA model, the overall structure,
characterized by an n = 3.4 polytrope, is similar. Impor-
tantly, this structure exhibits greater stability compared
to that of the primary star. Lastly, we assign a molecu-
lar weight of µ2 = 0.62 to the secondary star, based on
the average molecular weight of the MESA model.
3. RESULTS
In this section, we present the findings from our sim-
ulations of the merger and post-merger evolution of a
16+4 M⊙ binary system. Our analysis focuses on three
key aspects. First, in subsection 3.1, we examine the bi-
nary’s evolution leading up to the merger. This includes
the behavior of the binary system as it approaches the
merging stage. Second, in subsection 3.2, we investi-
gate the amount of mass that becomes unbound due
to the binary interaction. We analyze the properties of
the mass loss resulting from the merger, including the
morphology, geometry, and dynamics of the outflows.
Finally, in subsection 3.3, we explore the characteristics
of the post-merger phase. We perform long-term nu-
clear evolution simulations using the MESA code, uti-
lizing the averaged three-dimensional post-merger struc-
ture from Octo-Tiger to generate a one-dimensional
profile. This allows us to study the properties of the
post-merger system in terms of its nuclear evolution. By
examining these three aspects, we gain a comprehensive
understanding of the merger and post-merger processes
in the 16+4 M⊙ merger model.
7. Betelgeuse as a merger 7
0 2 4
Radius [R ]
10−7
10−4
10−1
Density
[g/cm
3
]
k xBinary
MESA
0 2 4
Radius [R ]
107
1011
1015
Pressure
[erg/cm
3
]
k xBinary
MESA
0 2 4
Radius [R ]
105
106
107
105
106
107
Temperature
[K]
k xBinary
MESA
Figure 4. Density (left), pressure, (center), and temperature (right) as a function of radius of the initial secondary star in our
simulation. We plot lines along the binary axis, xBinary (lines that go from the center of the secondary star to the direction of
the primary star center; blue circles), as well as the 1D MESA profile (solid red line) for comparison
3.1. Orbital Evolution
To accelerate the merger process and minimize com-
putational time, we employ a driving mechanism in the
binary system. Following the approach outlined in Mar-
cello et al. (2021), we extract angular momentum from
the grid at a constant rate of 1% per initial orbit. This
manipulation leads to a reduction in the orbital sep-
aration and facilitates a more significant mass transfer
between the stars. Without this driving mechanism, the
system would undergo numerous orbits, potentially sev-
eral hundreds, before a merger occurs. Given our cur-
rent resources and time constraints, simulating such a
prolonged evolution would be impractical.
In Figure 5 we plot the conservation of mass (left),
energy (center), and angular momentum (right) in the
Octo-Tiger merger simulation. In this plot, we ex-
amine the changes in total mass, total energy, and to-
tal z-angular momentum over time, denoted as ∆M,
∆E, and ∆Jz respectively. These quantities are cal-
culated by comparing the current values to their ini-
tial values in the grid: ∆M = M(t) + Mout(t) − M0,
∆E = E(t) + Eout(t) − E0, and ∆Jz = Jz(t) − J0
z .
Here, M0, E0, and J0
z represent the initial total mass,
total energy, and total z-angular momentum in the grid.
Additionally, Mout(t) and Eout(t) account for the mass
and energy that have left the grid, respectively. For
energy and angular momentum, we assess their conser-
vation only after discontinuing the driving mechanism
at t = 46P0. Our findings reveal that mass and energy
are conserved at a precision level of 10−6
. However, due
to numerical viscosity-induced torques during and after
the merger, the total z-angular momentum increases by
5%. Furthermore, as mass leaves the grid, the angular
momentum decreases by 20%. Although quantifying the
exact amount of z-angular momentum leaving the grid
is challenging, our results indicate that angular momen-
tum is still conserved at a level of approximately 5%.
As described in Marcello et al. (2021) we use an itera-
tive post-processing method to identify the cells that
belong to each star. This diagnostics scheme allows
us to calculate the system’s orbital properties, like or-
bital separation and orbital angular momentum, as well
as the mass, energy and spin of each star. We im-
proved the technique and instead of just iterating over
a fixed number of iterations we iterate until the stars’
masses (M1 and M2) and the orbital separation (a) con-
verged, i.e, when the values in the current iteration
are at most within 10−5
of the values in the previous
one. Note that when the system approaches the final
merger, it becomes increasingly difficult to differenti-
ate between the two stars and the diagnostics method
cannot be reliably used. We typically find that this oc-
curs when the binary frequency, as calculated by the
center of mass, (x1,2
, y1,2
, z1,2
) and center of mass ve-
locity (v1,2
x , v1,2
y , v1,2
z ) of each star, Ωorb = jz,orb/a2
=
[(x2
− x1
)(v2
y − v1
y) − (y2
− y1
)(v2
x − v1
x)]/a2
, falls be-
low half of the nominal Keplerian frequency, Ωkep =
p
G(M1 + M2)/a3. This is to be expected as the donor’s
envelope is tidally disrupted, and much of its mass in-
creasingly lags behind its center of mass. Therefore we
may define the binary merging time as when the binary
frequency falls below half of the nominal Keplerian fre-
quency.
In Figure 6 we plot orbital separation, orbital angu-
lar momentum, mass losses (∆M = M(t) − M(0)), and
mass transfer rates as a function of time (in initial or-
bital period units, P0 = 26 days). All these quantities
were calculated using the diagnostics scheme discussed
in the previous paragraph. The mass transfer rates are
smoothed by the Savitzky-Golay filter (Savitzky & Go-
lay 1964) with a window size of 2P0.
As anticipated, the presence of driving in the sys-
tem leads to an initial decrease in the orbital separation
(panel a) and orbital angular momentum (panel b) that
follows a nearly linear trend. At this stage, the primary
star overflows its RL, resulting in a high mass loss rate
of 10−4
− 5 × 10−1
M⊙ yr−1
(panel d, indicated by the
dashed orange line). However, only a small portion of
8. 8 Shiber et al.
0 25 50
t/P0
10−9
10−8
10−7
10−6
|∆M/M
0
|
50 55 60
t/P0
10−7
10−6
10−5
10−7
10−6
10−5
|∆E/E
0
|
50 55 60
t/P0
−0.1
0.0
∆J
z
/J
0
z
Figure 5. Conservation of mass, energy, and angular momentum. Note that the in the angular momentum plot we do not take
into account angular momentum losses due to gas that flows outside of the simulation domain.
0 20 40
t/P0
0
50
100
a
[R
]
(a)
0 20 40
t/P0
0.0
0.5
1.0
J
orb
/J
0
orb
(b)
0 20 40
t/P0
0.0
0.5
1.0
M
[M
]
−∆(M1 + M2)
−∆M1
∆M2
(c)
0 20 40
t/P0
10−4
10−2
100
10−4
10−3
10−2
10−1
100
101
Ṁ
[M
yr
−1
]
−(Ṁ1 + Ṁ2)
−Ṁ1
Ṁ2
(d)
Figure 6. Binary diagnostics plots as a function of time. (a) Orbital separation; (b) Orbital angular momentum; (c) mass
losses, where ∆M = M(t) − M(0); and (d) mass transfer rates. The primary star (star 1) looses mass (dashed orange lines),
however, the secondary star only accretes a fraction of it (dashed-dotted green lines) and the rest leaks through L2 and leaves
the system (blue solid lines). As the mass transfer is otherwise stable we continuously extract angular momentum at a rate of
1% per initial orbit to expedite the merger (see discussion on the stability of mass transfer in appendix B). The system merges
after 45.96 initial periods (P0 = 26 days)
9. Betelgeuse as a merger 9
this lost mass is accreted by the secondary star (green
dash-dotted line). Surprisingly, the system experiences
a net loss of mass (blue solid line) rather than a net
gain by the secondary. As a result, the mass transfer
rate does not increase by much, necessitating continu-
ous driving to bring the system into contact and trigger
the merger. This continuous driving causes the system’s
center of mass to spiral-out of the center of the grid to
a distance of ∼ 15R⊙ by the time of the merger. In
the vertical direction, the system’s center of mass is not
affected by this driving and it moves less than the size
of one grid cell.
The mass loss from the primary star intensifies as the
orbital separation decreases and its RL shrinks. The
accretion rate onto the secondary star increases over
time as well, however, it settles down on a level of
∼ 10−2
M⊙ yr−1
, probably because the secondary star
cannot accommodate a faster accretion, and the mass
lost by the primary star escapes through L2 rather than
accreted. These accretion rates are consistent with other
studies that conduct 3D hydrodynamic simulations of
CEE, although with a red giant and less massive pri-
mary star, where they find accretion rates onto a MS
secondary star of 10−3
−101
M⊙ yr−1
(Chamandy et al.
2018; Shiber et al. 2019; López-Cámara et al. 2022). A
MS star that accretes mass at a high rate might launch
jets (Shiber et al. 2016), which can help in unbinding the
envelope and perhaps even postpone the fast plunge-
in (grazing envelope evolution; Soker 2015, Shiber &
Soker 2018, Shiber et al. 2019). However, we do not
include jets in our simulation and disregard the jets’
energy which can be approximated by taking a small
factor η of the accretion energy onto the secondary star,
Ejets = ηGM2∆M2/R2 ≃ η×2×1047
ergs. We also note
that jets may act as a positive feedback that increases
the accretion rate onto the companion, either by remov-
ing energy and decreasing the pressure in the vicinity
of the accreting star, or by pushing mass towards the
orbital plane where most of the accretion takes place. If
this positive feedback is substantial, the increase in the
accretion rate would result in higher jets’ energy and the
role of jets can become more important.
During the later stages of the simulation, when the
secondary star penetrates the envelope of the primary
star (approximately at t = 30P0), the hydrodynamic
and gravitational drag forces cause the secondary star
to spiral further into the primary’s envelope. Eventually,
it merges with the helium (He) core of the primary star,
which occurs within a timescale of approximately 15P0
or around 1 year. By this point, a total mass of approx-
imately ≲ 1.3M⊙ is ejected from the system (panel (c)),
where some of it actually originated from the secondary
star. This mass carries an energy of 6.5×1046
ergs, and
z-angular momentum of 0.3J0
orb, where J0
orb, is the initial
orbital angular momentum and equals 8.5 × 1053
ergs s.
However, not all of this mass is necessarily unbound or
remains unbound. In the subsequent subsection (subsec-
tion 3.2), we will demonstrate that approximately half
of this amount of mass becomes unbound during the
merger process and ultimately flows out of the compu-
tational grid, contributing to the formation of a merge-
burst transient event.
In Figures 7 and 8 we show density map slices along
the equatorial (orbital) and meridional plane, respec-
tively, at nine different times as denoted at the lower-
left corner of each panel: 2.5P0, 17.5P0, 25.0P0, 30.0P0,
35.0P0, 40.0P0, 44.2P0, 45.9P0, and 47.0P0. We also
plot the velocity field scaled by velocity magnitude (in
red; key shown on the upper right corner) to highlight
details of the flow1
. The plotted velocities at the six first
panels (i.e., t ≤ 30P0) are measured with respect to a
frame that rotates at the momentary orbital frequency
(i.e., frame of reference that rotates with the binary).
In the three last panels (t > 30P0; closer to the merger
time and afterwards), the plotted velocities are mea-
sured with respect to a frame that rotates at the initial
orbital frequency (i.e., a frame of reference that rotates
with the grid). The binary and as a consequence the
grid itself both rotate at the counter clock-wise direc-
tion. Each panel is centered around the system’s center
of mass, and the green cross symbol denotes the location
of the primary’s star center of mass.
These plots illustrate the accumulation of mass around
the secondary star and the system’s overall mass loss
through L2. Initially, mass flow originating from the
primary star begins to envelop the secondary star, while
mass escaping through L2 forms a spiral-shaped arm
(t = 0−30P0). As the secondary star spirals inward and
approaches the envelope of the primary star, a common
envelope configuration is established (t = 30P0). Over
time, hydrodynamical drag and gravitational forces act
upon the system, driving the secondary star deeper
into the envelope of the primary star, until the sec-
ondary tidally disrupts the primary’s helium (He) core
at t = 45.96P0. Subsequently, the secondary plunges
into and mixes with the remnant helium core of the pri-
mary over the following couple of P0. However, this final
evolution is a consequence of the choices we had to make
for numerical reasons, which resulted in a secondary core
denser than the primary core. Since the central density
of the primary star is ∼ 30 times denser than the sec-
1 Movies of the simulation can be obtained via this link
10. 10 Shiber et al.
50
0
50
y
[
R
¯
]
2.5 17.5
150 km/s
25.0
50
0
50
y
[
R
¯
]
30.0 35.0 40.0
50 0 50
x [R¯ ]
50
0
50
y
[
R
¯
]
44.2
50 0 50
x [R¯ ]
45.9
50 0 50
x [R¯ ]
47.0
10-12
10-10
10-8
10-6
10-4
10-2
100
Density
³
g
cm
3
´
Figure 7. Equatorial density slices at nine different times throughout the evolution up to the dynamical merger phase: 2.5P0,
17.5P0, 25.0P0, 30.0P0, 35.0P0, 40.0P0, 44.2P0, 45.9P0, and 47.0P0. We also plot the velocity field scaled by velocity magnitude
(in red; key shown on the upper right corner) to highlight details of the flow. Velocities at the six first panels are measured in
the frame rotating with momentary binary frequency, while in the three last panels they are measured in the frame rotating with
the initial binary frequency. The panels are centered around the system’s center of mass, and the green cross symbol denotes
the location of the primary’s star center of mass. The system rotates counter clock-wise
ondary’s star central density, according to the MESA
models, in a more realistic evolution, it would be the
primary core that disrupts the secondary. Therefore we
are not able to say anything definite about the potential
rejuvenation of the primary core.
Our finding that a substantial portion of the mass
leaving the primary star is expelled through the L2 La-
grange point and is subsequently lost from the system
instead of being accreted onto the secondary star could
drastically affect the stability of the mass transfer. A
conservative mass transfer in its simplest form dictates
that a mass that passed from the more massive to the
less massive star leads to a dynamical unstable mass
transfer and to the formation of a CE. A more sophis-
ticated analysis includes the response of each star to
its mass loss or mass gain, respectively. In our spe-
cific case, the primary star possesses a predominantly
radiative envelope that we approximate using a poly-
tropic index of n1 = 4.1. Consequently, its adiabatic
mass-radius exponent, denoted as ζad and calculated as
11. Betelgeuse as a merger 11
50
0
50
z
(
R
¯
)
2.5 17.5
150 km/s
25.0
50
0
50
z
(
R
¯
)
30.0 35.0 40.0
50 0 50
x0
(R¯)
50
0
50
z
(
R
¯
)
44.2
50 0 50
x0
(R¯)
45.9
50 0 50
x0
(R¯)
47.0
10-12
10-10
10-8
10-6
10-4
10-2
100
Density
³
g
cm
3
´
Figure 8. Meridional density slices at nine different times throughout the evolution up to the dynamical merger phase. Times
and symbols are like in Figure 7
(d log R/d log M)ad, is approximately 2.82 and the pri-
mary radius will shrink when it looses mass. This needs
to be compared with the mass-radius exponent associ-
ated with the Roche lobe, denoted as ζRL, which is esti-
mated to be around 2.13(M1/M2) − 1.67 ≈ 6.5 accord-
ing to Tout et al. (1997) for conservative mass transfer.
Therefore, based on this criterion, the RL will shrink
faster than the primary star, and the mass transfer be-
tween the stars should be dynamically unstable.
However, our simulations reveal that the assumption
that all the mass lost from the donor star is accreted
by the secondary does not hold. This phenomenon can
greatly enhance the stability of the mass transfer pro-
cess, depending on the fraction of mass accreted, f, as
well as on angular momentum losses through L2. A care-
ful calculation of the stability of mass transfer for non-
conservative cases shows that in the absence of angular
momentum losses, f < fmax = 0.53 would be dynami-
cally stable. Angular momentum losses act to destabi-
lize the mass transfer and thus effectively reduces fmax
(for a detailed calculation we refer to appendix B). It
is therefore plausible that a mass transfer on a ther-
mal timescale is expected to occur under these condi-
tions. Once the primary’s envelope expands further and
reaches the size of the orbit, the mass transfer will tran-
sition into a dynamically unstable regime.
12. 12 Shiber et al.
Moreover, even if the conditions are such that the
mass transfer is dynamically unstable, it could be that
the mass transfer rate will only slowly increase, imply-
ing that numerous orbits are still required to simulate
before the actual merger will take place. It is not triv-
ial to know a priori the amount of driving required to
achieve a specific mass transfer rate nor to predict the
subsequent behavior of the mass transfer rate once the
driving is stopped. In fact we tried to stop the driving at
several instances during the evolution, finding that the
following evolution would be still too long to simulate.
In practice we applied the driving mechanism continu-
ously until the system merged. Notably, the behavior
observed while driving the system to contact (and be-
yond) suggests that the initial binary separation should
have been chosen smaller, around 50R⊙ instead of the
100R⊙ estimated from the point at which the primary
fills its RL. However, a smaller initial separation can re-
sult in a lower final equatorial velocity, as demonstrated
in Chatzopoulos et al. (2020) through Equation 5 and
Figure 1.
3.2. Mergerburst and outflow
During the common envelope evolution, as the sec-
ondary star interacts with the envelope of the primary,
there is an exchange of orbital and thermal energy. This
process ultimately leads to the merger of the secondary
star with the helium core of the primary. As the merger
occurs, a powerful dynamical pulse is triggered that
propagates through the envelope of the primary. Under
certain conditions, this pulse can induce significant mass
loss from the system. The gravitational energy released
during the merger is primarily converted into kinetic en-
ergy, driving the high-speed outflow of gas from the pri-
mary’s envelope. Additionally, a portion of the released
energy is transformed into internal or thermal energy.
As a result, the gas within the primary’s envelope is ex-
pelled at high velocities, and a substantial fraction of it
attains enough energy to surpass the gravitational po-
tential barrier. Consequently, this gas becomes unbound
from the system and is no longer gravitationally bound.
Figure 9 illustrates the quantity of mass that becomes
unbound within the grid over time. We focus on the ten
orbits preceding the merger time, Tmerge = 45.96P0, and
the subsequent period, as only a small amount of mass
becomes unbound during earlier times. We establish two
criteria for identifying unbound mass. The first criterion
considers gas as unbound when its kinetic energy plus
gravitational energy, Ek + Eg, is positive (depicted by
solid lines). The second criterion incorporates internal
energy, where gas is considered unbound when its to-
tal energy, Ek + Eg + Eint, is positive (represented by
−10 0 10
(t − Tmerge) /P0
0.0
0.2
0.4
0.6
Unbound
Mass
[M
]
total
star 1
star 2
comulative
total (inc. Eint)
star 1 (inc. Eint)
star 2 (inc. Eint)
comulative (inc. Eint)
grid mass loss
Figure 9. The unbound mass as a function of time in our
simulation (solid lines). The mass that left the grid is also
plotted (magenta dashed-dotted line). The cumulative un-
bound mass (brown lines) sums unbound gas in the grid plus
the mass that left the grid, assuming that all the mass that
left the grid, left it unbound and remains unbound after-
wards. Including internal (thermal) energy only slightly in-
crease the unbound mass (dashed lines)
dashed lines). It is important to note that due to the
finite-volume nature of our grid, the unbound mass even-
tually flows out of the grid, despite its relatively large
size. Consequently, we include in the plot the quantity
of mass that exits the grid (indicated by dash-dotted
lines).
We observe that approximately ∼ 0.6M⊙ of mass be-
comes unbound within the grid. The majority of this
unbinding occurs at the moment of merger and during
a time scale of one initial orbital period (P0 = 26 days).
When accounting for internal energy in the energy bal-
ance, the amount of unbound mass is only slightly
higher. Assuming that all the mass leaving the grid
remains unbound, the maximum estimate of unbound
mass is approximately ∼ 0.68 M⊙ (indicated by brown-
colored lines in Figure 9). This corresponds to approx-
imately ∼ 0.07 of the mass of the primary’s envelope
or ∼ 0.03 of the total stellar mass of the system. Fur-
thermore, a smaller phase of unbinding, approximately
∼ 0.02 M⊙, occurs prior to the merger (beginning at
t = Tmerge − 5P0 and decaying until t = Tmerge, allow-
ing all the unbound gas to escape the grid before the
merging time).
Interestingly, during the pre-merger unbinding phase,
all the unbound mass originates from the primary star
(depicted by green lines in Figure 9, labeled as ’star 1’
in the legend). However, after the merger, when the
majority of the unbinding occurs, only approximately
∼ 2/3 of the unbound mass originates from the primary
star, while the remaining ∼ 1/3 originates from the sec-
13. Betelgeuse as a merger 13
ondary star (indicated by red lines, labeled as ’star 2’ in
the legend). This finding suggests that the common en-
velope interaction can unbind a portion of the spiraling-
in secondary star’s mass (approximately 0.2M⊙ out of
the 4M⊙, which is 5%), highlighting the need for fu-
ture studies to consider this effect rather than relying
solely on the simple α formalism often used. Such re-
sults, which cannot be captured when representing the
secondary star as a point particle, warrant further in-
vestigation.
The fraction of the primary’s envelope that becomes
unbound (7%) is relatively smaller compared to find-
ings from previous studies on common envelope evolu-
tion of massive stars. However, in those studies they
include some extra sources of energies that our simu-
lation does not account such as recombination energy,
radiation energy, and jets (Lau et al. 2022a,b; Moreno
et al. 2022; Schreier et al. 2021). Other previous works
that do not include additional energy sources find ejec-
tion values more similar to ours (although for a low mass
primary star; e.g., Passy et al. 2012; Iaconi et al. 2017;
Reichardt et al. 2019; Shiber et al. 2019, and Sand et al.
2020). Another possible explanation stems from the fact
that our primary has not evolved yet to become a RSG
and thus its envelope possesses much higher binding en-
ergy compared to the binding energy its envelope will
posses when it will evolve to be a RSG star (Klencki
et al. 2021). Other studies deliberately chose primary
stars during its RSG phase and at maximal expansion
to ease the envelope removal (Lau et al. 2022a,b; Moreno
et al. 2022; Ricker et al. 2019).
In Figures 10-12 we explore the geometrical structure
and kinematics of the unbound merger–driven outflow.
Figure 10 shows the average (inertial) velocities of these
unbound outflows as a function of time, where we fo-
cus at the same time-span as in Figure 9. We aver-
aged by mass over gas with positive kinetic plus gravi-
tational energy. These velocities can be compared with
the nominal escape velocity from the system vesc(r) =
p
2G(M1 + M2)/r ≃ 270 km/s·(r/100 R⊙)−1/2
, where
r is the distance from the system’s center of mass. Prior
to the merging time, Tmerge, the amount of unbound
mass is small and therefore does not contribute much
to the mergerburst. The unbound gas immediately af-
ter the merger escapes with radial velocities (solid blue
line) which peak at 310 km/sec but also spins at a tan-
gential velocity of 140 km/sec (dashed orange line).
As the outflow propagates further out it decelerates
due to the gravitational pull from the central, merged
object. The tangential velocity decays faster than the
radial velocity component. We assume for simplicity
that this unbound mass originated from a distance of
−10 0 10
(t − Tmerge) /P0
0
200
400
<
v
>
unbound
[km/s]
vr
vθ
vesc(rout)
0
10
20
r
out
(t)
=
r
0
+
R
v
r
dt
[AU]
rout (t)
Figure 10. Average unbound gas velocities and inferred ra-
dial distance as a function of time. The (solid) blue curve
denotes spherical radial velocity, vr, and the (dashed) or-
ange curve azimuthal spherical velocity, vθ. The (dotted)
red curve denotes the outflow average distance, rout, as calcu-
lated by integrating vr, rout = r0 +
R
vrdt with r0 being equal
to the initial separation 100 R⊙, while the (dashed) green
curve denotes the escape velocity at this distance, vesc(rout).
At each time the average velocity is a mass-averaged calcu-
lated only for unbound gas. The purple vertical line denotes
the time in which the outflow arrives to the computational
grid boundary
the initial orbital separation, r0 = a0 = 100 R⊙ and
integrate its radial velocity from the merging time and
onward to derive its radial distance, rout as a function of
time (red dotted line), rout = r0 +
R t
Tmerge
vrdt. We also
calculate the escape velocity at the instantaneous radial
distance of the outflow and show that the propagation
speed of the outflow remains greater than the escape
velocity at any time. A purple dashed vertical line at the
post-merger time of 3.6P0 = 93 days denotes the time
when the outflow arrives to the boundary of the grid.
Note that the fastest flow reach the boundary earlier
indicated by the peak in unbound mass (orange line in
Figure 9) at t ≃ 2P0 ≃ 52 days.
In Figure 11, we plot three-dimensional renderings of
the unbound gas density at six different times after the
merger. In each panel we plot densities at the range
of 10−8
− 10−12
g/cm3
(colored red to dark blue, re-
spectively, according to the color map). The point of
view is of an observer at the corner of the grid, i.e, at
(2000 R⊙, 2000 R⊙, 2000 R⊙), looking towards the grid’s
center.
Our simulation reveals that the outflow exhibits an
asymmetric expansion pattern and possesses a complex
inner structure. In the early stages (panels (a) and (b)),
a distinctive two-ring structure emerges, with one ring
located above and another below the equatorial plane
14. 14 Shiber et al.
T = 46.22 P0
1 AU
1.00×10 11
1.00×10 10
1.00×10 9
1.00×10 8
3.06×10 12
Density
(
g
cm
3
)
(a) t = Tmerge + 0.26P0
T = 46.33 P0
1 AU
1.00×10 11
1.00×10 10
1.00×10 9
1.00×10 8
3.06×10 12
Density
(
g
cm
3
)
(b) t = Tmerge + 0.37P0
T = 46.50 P0
1 AU
1.00×10 11
1.00×10 10
1.00×10 9
1.00×10 8
3.06×10 12
Density
(
g
cm
3
)
(c) t = Tmerge + 0.54P0
T = 46.75 P0
1 AU
1.00×10 11
1.00×10 10
1.00×10 9
1.00×10 8
3.06×10 12
Density
(
g
cm
3
)
(d) t = Tmerge + 0.79P0
T = 47.06 P0
1 AU
1.00×10 11
1.00×10 10
1.00×10 9
1.00×10 8
3.06×10 12
Density
(
g
cm
3
)
(e) t = Tmerge + 1.05P0
T = 47.50 P0
1 AU
1.00×10 11
1.00×10 10
1.00×10 9
1.00×10 8
3.06×10 12
Density
(
g
cm
3
)
(f) t = Tmerge + 1.54P0
Figure 11. Outflow structure. Three-dimensional renderings of unbound gas density (i.e., gas with Ek +Eg > 0), at six different
times: 0.26 P0 (7 days), 0.37 P0 (10 days), 0.54 P0 (14 days), 0.79 P0 (21 days), 1.05 P0 (27 days), and 1.54 P0 (40 days), after
the stars merged. Each panel presents densities at the range of 10−8
−10−12
g/cm3
(red to dark blue, respectively, and according
to the color map) as observed by a viewer at the corner of the grid looking towards the grid’s center. These renderings extend
up to an inner sphere of radius size 6.5 AU. A length scale of 1 AU is also plotted. The positive z-axis is directed upward.
(depicted in red). This structure expands over time
and remains visible in later stages (panel (e), repre-
sented by orange). During the process of the secondary
star’s spiraling-in (prior to its merger), gas accumulates
around it, causing the envelope to become inflated and
concentrated primarily towards lower latitudes. Conse-
quently, when the rapid outflow bursts out, it escapes
and expands more rapidly towards the poles, resulting in
the formation of a bipolar outflow structure. The bipo-
lar and clumpy ring-like morphology of the outflow is
reminiscent of circumstellar (CS) environments observed
around some massive star systems (i.e., η–Carina, Smith
& Ferland 2007) as well as supernova (SN) remnants like
SN1987A (Plait et al. 1995). A clumpy ring structure
has been also observed in several planetary nebulae (e.g.,
the necklace nebula; Corradi et al. 2011). However, in
our simulation, the unbound outflow forms two clumpy
rings, one above and another below the equatorial plane,
which expand to higher latitudes rather than an equa-
torial knotted-ring.
Lastly, Figure 12 presents a phase plot that displays
the distribution of unbound mass (in solar mass units)
within specific density and velocity ranges at three dif-
ferent time intervals following the merger: 0.37P0 (left
column), 0.79P0 (middle column), and 2.5P0 (right col-
umn). The first row of plots illustrates the mass distri-
bution in specific density and positive z-velocities bins,
while the second row depicts the mass distribution in
density and radial cylindrical velocities bins. These plots
provide insights into the kinematics of the outflow. It is
important to note that since only the positive z-direction
is depicted, the mass shown in these plots (first row) rep-
15. Betelgeuse as a merger 15
resents approximately half of the total unbound mass
within the grid.
During the early period up to t = Tmerge + 0.37P0
(left column), the outflow expands steadily without de-
celerating. This expansion can be observed in the phase
plots as a structure shifting to the left, to lower densi-
ties, without changing its shape. Subsequently, the ex-
pansion continues, but the outflow starts to decelerate
(the structure shifts to lower densities and lower veloci-
ties, in the middle column compared to left column). At
this stage, the fastest velocities are still primarily in the
z-direction. As the merger-burst reaches the boundary
of the grid, less unbound mass remains within the grid.
The fast outflow in the z-direction exits the grid first,
resulting in a more uniform velocity distribution (right
column). This can be seen in the phase plots of the right
columns, where a similar shape is observed between the
upper and lower panels. This analysis indicates that the
fastest velocities are predominantly aligned with the z-
direction.
Based on these results we can extrapolate how a neb-
ula produced by such a mergerburst will appear at later
stages. In Figure 13 we show the outflow peak den-
sity (left) and its distance from the merger (right) as a
function of time. The blue points are data points from
the hydrodynamic simulation while the orange curves
are extrapolation assuming homologous expansion, i.e.,
ρpeak ∼ t−3
, r ∼ t and disregarding interaction with the
interstellar medium.
In addition, we consider interaction of the outflow
with previous winds blown by the massive primary star
prior to the merger process. For that we use the equa-
tions by Chevalier & Fransson (1994). They developed
analytical formulas for the interaction of supernova-
driven outflows with winds and we downscale them for
mergerburst driven-outflows. We first fit the outflow
density profile in the simulation domain to two power-
laws. This yields a flat slope of δ = 1.8 within the inner
6.7 AU, and a steep slope of n = 11.9 beyond this radius,
which we round up to n = 12. The mass (M) and energy
(E) of the outflow is the total mass and energy lost from
the grid, i.e., 0.68 M⊙ and 1.8 × 1047
ergs, respectively.
As an estimation of the mass loss rate to winds we use
the last value as prescribed by the MESA model of our
primary star, Ṁ = 2 × 10−7
M⊙ yr−1
. We assume cir-
cumstellar density that decreases as r−s
, where s = 2,
and plug two possible wind velocities of 10 km/sec and
100 km/sec to equation 2.7 from Chevalier & Fransson
(1994) to derive the radius of peak densities shells, the
green and red curves on the right panel, respectively.
Lastly, we consider an interaction with a more pow-
erful mass-loss of Ṁ = 0.1 M⊙ yr−1
and assuming a
uniform wind profile, s = 0. As in Chatzopoulos et al.
(2012) (appendix B), we use a density scaling in the im-
mediate vicinity of the primary star and therefore obtain
r1 = Rp = 50 R⊙. We plug wind velocity of 10 km/sec
and the right constants for s = 0 and n = 12 from table
1 of Chevalier (1982) in equation B2 of Chatzopoulos
et al. (2012) to obtain the forward shock location as an
estimation for the radius of peak densities in this case.
We plot this radius as a function of time in dotted purple
line in the right panel of Figure 13.
From this figure we learn that if the merger will ex-
plode in a Core-collapse Supernova within the first few
years after the merger, the nebula can affect the su-
pernova lightcurve via interaction. At later times the
nebula dissolves and would be difficult to detect nor to
play any important role.
3.3. Merger properties and further evolution
As mentioned in the Introduction (Section 1), obser-
vational evidence supports the presence of rapid surface
velocities in a few giant and supergiant stars. For in-
stance, studies on Betelgeuse have demonstrated (Chat-
zopoulos et al. 2020; Sullivan et al. 2020) that a previous
merger between a pre-main sequence massive star with a
mass of approximately 15−17M⊙ and a low-mass main-
sequence companion with a mass of around 1 − 4M⊙
could account for its implied high rotation rate. In this
study, we aim to investigate whether the merger product
in our simulation has the potential to evolve into a star
similar to Betelgeuse. In this subsection, we explore the
interaction between the secondary star and the primary
star’s envelope during the spiral-in process, which leads
to the transfer of orbital angular momentum to the en-
velope. As a result, immediately following the merger,
the envelope becomes inflated and rotates faster than
its initial state. However, in order to determine whether
this dynamical spin-up has any long-term effects on the
significantly longer thermal and nuclear timescales that
cannot be simulated hydrodynamically, we need to uti-
lize a 1D representation of the post-merger object in
a stellar evolution code. In Subsection 3.3.1, we ana-
lyze the post-merger structure within the hydrodynamic
simulation, while in Subsection 3.3.2, we investigate the
long-term evolution by importing the post-merger struc-
ture into the MESA stellar evolution code.
3.3.1. Immediate dynamical properties
Figure 14 illustrates the one-dimensional averaged
structure of the merger. To obtain these profiles, we per-
formed a mass average over the azimuthal angle around
the point of maximum density, which we define as the
center of the merger, and only considered data from the
equatorial plane. The following quantities are plotted
16. 16 Shiber et al.
200
400
600
v
z
[km
/
s] t=46.33 P0 t=46.75 P0 t=48.46 P0
10-11 10-8
ρ [g/cm3]
200
400
600
v
R
[km
/
s]
10-11 10-8
ρ [g/cm3]
10-11 10-8
ρ [g/cm3]
10-7
10-6
10-5
10-4
10-3
10-2
unbound
mass
(
M
¯
)
Figure 12. Outflow velocities at the z (upper panels) and cylindrical radius (bottom panels) directions, at three different
times: 0.37 P0 (10 days), 0.79 P0 (21 days), and 2.5 P0 (65 days) after the merger time. Each panel plots the amount of
mass (in solar mass) the outflow, i.e, gas with Ek + Eg > 0, has at a certain densities and velocities range. Following the
merger, the mergerburst first expands but sustains its velocities (t = Tmerge + 0.37P0, left panels), expands and decelerates
(t = Tmerge + 0.79P0, middle panels), and eventually reaches the grid boundary and escapes t = Tmerge + 2.5P0, right panels.
The fastest flow of the mergerburst is pointed toward the z-direction, as is reflected by the apparent bipolar structure
as a function of the distance from the merger’s center
(from upper left to lower right): specific angular mo-
mentum, angular velocity, density, and temperature. It
is important to note that the specific angular momentum
and angular velocity are computed with respect to the
merger’s center, meaning that the radius represents the
distance from this point, and the velocities are corrected
by subtracting the velocities of this point from the iner-
tial velocities. Averaging only over the equatorial plane
may lead to an overestimation of rotation values since
the deposition of orbital angular momentum primarily
occurs around the orbital plane. Consequently, it is ex-
pected that rotation would be slower at higher latitudes.
However, as the post-merger object undergoes dynamic
relaxation within a few orbits, the bound gas gradually
becomes more spherically symmetric, causing the redis-
tribution of angular momentum accordingly. Thus, only
minor differences between latitudes are expected during
this phase. In each panel, two profiles corresponding to
two different times, namely 0.5P0 (13 days; blue solid
17. Betelgeuse as a merger 17
10−1
101
103
105
t − Tmerge [yr]
10−31
10−27
10−23
10−19
10−15
10−11
10−7
Density
[g/cm
3
]
ρpeak(t)
ρpeak(t) homologous
10−1
101
103
105
t − Tmerge [yr]
1014
1016
1018
1020
r
[cm]
r(t)
r(t) homologous
vw = 10 km/s, s = 2
vw = 100 km/s, s = 2
vw = 10 km/s, s = 0
vw = 10 km/s, s = 2
vw = 100 km/s, s = 2
vw = 10 km/s, s = 0
Figure 13. Extrapolation of the mergerburst to later stages post-merger. Left panel: Peak density. Right panel: Distance of
the peak density from the post-merger object. The blue points are data points from the hydrodynamic simulation while the
orange curves are extrapolation assuming homologous expansion. We also consider interaction of the mergerburst with winds
blown by the massive primary star prior to the merger process with wind velocity vw and a profile that decreases as r−s
(see
details in the text)
crosses) and 5P0 (130 days; orange solid circles) after
the merging time, are displayed.
As the post-merger object undergoes dynamic re-
laxation, its internal structure gradually becomes
smoother, as evident in the smoother temperature pro-
file. The orange lines in the plots start from further out
due to grid derefinement in the central regions follow-
ing the merger. This de-refinement leads to a drop in
central density but also facilitates the redistribution of
angular momentum. To assess the effects of the merger
on the post-merger object, we compare the specific an-
gular momentum and density profiles with those of the
original MESA primary star’s model (shown as green
dashed lines, denoted as “pre” in the legend). The spe-
cific angular momentum gain of the envelope resulting
from the merger is clearly visible in the specific angular
momentum plot. Moreover, the envelope becomes in-
flated, and the density contour of 10−9
g/cm3
expands
from 50R⊙ to 430 R⊙. In the plot, we also include
the specific angular momentum profile computed ana-
lytically (using Equations 13 and 14 from Chatzopoulos
et al. 2020), shown as a dashed-dotted green line and
denoted as ”post” in the legend. This analytical profile
was used in Chatzopoulos et al. (2020) to simulate the
merger starting from the pre-merger 1D profile. Here,
we include it for comparison purposes. It is worth not-
ing that this profile rapidly increases at 1012
cm and
further out, due to the steep density decline in these re-
gions in the pre-merger primary profile. The specific an-
gular momentum plot conclusively highlights the benefit
of simulating the merger in a dynamical three-dimension
simulation over a prescribed 1D model, which could not
account important features of the merger such as enve-
lope expansion.
It is worth mentioning though, that as a consequence
of the continuous driving we apply on the system, the
merger possesses less angular momentum than it would
have without the driving. Specifically, the driving mech-
anisms absorbs almost 50% of the initial orbital angular
momentum. Outflows carried an additional ∼ 20% of
the angular momentum and the merger therefore ac-
quires only 30% of the orbital angular momentum that
is initially available. This affects the specific angu-
lar momentum of the merger (and its angular veloc-
ity), which are probably underestimated and could be
higher. In particular, this is true for the profiles at
t = Tmerge + 0.5P0 before viscosity torques and grid de-
refinement introduce some numerical angular momen-
tum increase (at the level of ∼5%)
To emphasize the dynamic spin-up of the envelope, we
present the angular velocity profile of the envelope over
time in Figure 15. Prior to the merger, the angular ve-
locity is calculated relative to the point of maximal den-
sity, which belongs to the primary star and is determined
using the diagnostics scheme described in Section 2. Fol-
lowing the merger, the angular velocity is calculated rel-
ative to the center of the post-merger star. Additionally,
we include the orbital separation as a function of time,
represented by a gray line. This figure reveals that the
envelope in regions near the secondary star undergoes a
spin-up process during the slow spiraling-in phase. As
the binary system approaches contact and enters the fast
spiraling-in phase, the rate of angular momentum gain
increases. Subsequently, during grid de-refinements, the
angular momentum redistributes within the system. As
a result, the inner region of approximately 50 R⊙ ex-
hibits a significant increase in rotational velocities, ex-
ceeding their initial rotation by more than an order of
magnitude.
18. 18 Shiber et al.
1010
1012
1010
1011
1012
1013
Radius [cm]
1014
1017
1020
j
cm
2
s
−1
Tmerge + 0.5P0
Tmerge + 5P0
1D pre
1D post
1D pre
1D post
1010
1012
1010
1011
1012
1013
Radius [cm]
10−7
10−5
Ω
[rad/sec]
Tmerge + 0.5P0
Tmerge + 5P0
1010
1012
1010
1011
1012
1013
Radius [cm]
10−12
10−7
10−2
103
Density
[g/cm
3
]
Tmerge + 0.5P0
Tmerge + 5P0
1D pre
1010
1012
1010
1011
1012
1013
Radius [cm]
104
106
103
104
105
106
107
Temperature
[K]
Tmerge + 0.5P0
Tmerge + 5P0
Figure 14. Post-merger star’s structure azimuthally averaged over the equatorial plane at 0.5 (blue curves) and 5 (orange
curves) orbits past merger. From the upper-left panel to the lower-right panel presented specific angular momentum; Angular
velocity; Density; and Temperature. The density and specific angular momentum of the primary initial (MESA) model is also
plotted (dashed green lines). We compare the specific angular momentum of the merger (as a result of our hydrodynamic
simulation; upper-left panel, blue and orange lines) with the post-merger profile as calculated by Equations 13 and 14 in
Chatzopoulos et al. (2020) and based on the pre-merger one-dimensional profile of the primary (green dashed-dotted line in the
same panel)
0 20 40
t/P0
1011
1012
1013
1014
Radius
[cm]
10−8
10−7
10−6
10−5
10−4
Ω
[rad/s]
Figure 15. Illustration of the primary envelope spin-up
during the merger process. The color scale corresponds to the
angular velocity with respect to the primary’s core position
averaged at the equatorial plane. The color map is in units
of rad/s. Time (in units of initial periods, P0) is plotted on
the x-axis. Distance from the primary core (in units of cm)
is plotted on the y-axis. The orbital separation as a function
of time is overplotted as a gray curve
3.3.2. Long term nuclear evolution
To study the long-term evolution of the merger on a
nuclear timescale, we import the averaged 1D structure
of the merger into the MESA stellar evolution code.
This is achieved by performing a mass-weighted spher-
ical averaging procedure and importing the system 5
initial orbits after the merger event. The resulting pro-
files of entropy, specific angular momentum, and com-
position serve as inputs for MESA. However, due to
insufficient resolution in the inner regions of the hydro-
dynamical simulation, we replace the inner 9.6M⊙ of
the entropy profile with a core structure from a similar
star evolved in MESA (representing the primary’s pre-
merger/original input structure) that matches in terms
of age, mass, and radius. Assuming that the chemi-
cal composition remains unchanged by the merger, we
also import the abundance profile from the MESA pre-
merger model. The specific angular momentum profile
is directly imported from the Octo-Tiger model using
cylindrical shell averages. After spherically averaging
the bound mass of the post-merger object, the resulting
mass of the post-merger is 18.6M⊙
19. Betelgeuse as a merger 19
Once we have obtained the necessary profiles, we use
the external model relaxation procedures in MESA to
create a single star with a structure similar to our post-
merger object. Figure 16 illustrates the comparison be-
tween our input data and the resulting relaxed struc-
ture. It can be observed that all three profiles relax to a
state that closely matches the input structure. However,
it is important to note that the same entropy profile
in MESA will yield a different temperature and den-
sity profile compared to Octo-Tiger due to the differ-
ences in equation of state (EoS) and the requirement of
hydrostatic equilibrium (HSE) in MESA. Additionally,
the inclusion of radiation effects and tabulated opac-
ity in MESA leads to a larger relaxed structure com-
pared to the post-merger structure observed in Octo-
Tiger. The disparities in the density and temperature
profiles are evident in Figure 16. It should be mentioned
that due to the aforementioned core resolution issue, the
Octo-Tiger core does not have a sufficient tempera-
ture for helium burning. Conversely, the MESA profile
suggests that the primary should be undergoing helium
burning. It is important to acknowledge that although
the post-merger object also possesses a core that is cur-
rently too cool for helium burning, the structure has not
yet fully settled after the relaxation procedure, and the
star will contract, resulting in a hotter core.
After relaxing the post-merger into MESA, we allow
the star to dynamically settle and then evolve over nu-
clear timescales. During the evolution we use the Dutch
wind prescription, which uses the de Jegar prescrip-
tion for effective temperatures less than 8000K (de Jager
et al. 1988), and the Vink wind prescription for higher
effective temperatures (Vink et al. 2001). Typically, for
non-rotating models, a standard value of the wind scal-
ing factor is 0.8. This could be lower for rotating models
so we use a value of 0.4. Heger et al. (2000) give an ana-
lytical expression for enhanced mass loss due to rotation,
which is utilized by default in MESA version r21.12.1,
of the following form:
Ṁ = Ṁ0
1
1 − v/vcrit
ξ
(1)
Where Ṁ0 is the mass loss without rotation, v is the sur-
face rotation, vcrit is the critical surface rotation, and ξ
is the power factor (the default value is 0.43). Following
some of the parameters used for the MESA test suite
options, we use the Cox MLT option (Cox Giuli 1968).
We include the Ledoux criterion and use a mixing length
parameter of 1.6. We also include the effects of semicon-
vection and thermohaline mixing, but do not focus on
overshooting.
Some of the most important set of parameters for this
study are the effects of rotationally induced mixing for
both chemical mixing and angular momentum diffusion.
Because the surface of the star is spun up due to the co-
alescence of the secondary into the envelope of the pri-
mary, it is important that not too much angular momen-
tum is diffused downward toward the core. The types
of rotationally induced mixing we use are Solberg Hoi-
land (SH), Secular Shear Instability (SSI), Eddington-
Sweet Circulation (ES), and Goldreich-Schubert-Fricke
Instability (GSF) which are all described in Heger et al.
(2000). We also use Spruit-Taylor dynamo action (ST)
of Heger et al. (2005) which includes the effects of mag-
netic fields, but we note that there is a lot of uncertainty
regarding the strength and effect of magnetic fields for
giant stars. Finally, the overall coefficient which is mul-
tiplied by the sum of the diffusion due to all of the above
mixing effects is set to 1/30 according to the recommen-
dation of Heger et al. (2000).
When evolving the post-merger in MESA we vary
the efficiency of rotationally induced diffusion. The rea-
son for this is these effects are inherently 3-dimensional,
and their use in MESA is based on the work of Heger
et al. (2000), who approximated 1D diffusion coefficients
for each process. In addition, we acknowledge that in
the case of a star merger, most of the angular momen-
tum deposition occurs over the equatorial plane and non
homogeneously throughout the primary star’s envelope.
The efficiency factors we vary are used in order to ac-
count for the uncertainty of the effectiveness of diffusion
for each of these mechanisms. This method of simulat-
ing mixing is known as the diffusion approximation and
Paxton et al. (2013) note that there is another method
they refer to as the diffusion-advection approach. While
these two methods have nearly identical chemical mix-
ing, the transport of angular momentum can vary sig-
nificantly. More details regarding this other method of
angular momentum diffusion can be found in Maeder
Zahn (1998) and Zahn (1992). A summary of our model
parameters, the results, and Betelgeuse observations are
shown in Table 1.
The post-merger evolution is found to be primarily in-
fluenced by the viscosity coefficients associated with the
ST and ES mechanisms. These mechanisms play a dom-
inant role in the outer regions of the post-merger star’s
envelope, facilitating the efficient transport of excess an-
gular momentum towards the inner regions. As a result,
they significantly reduce the equatorial rotation rate of
the star. However, we have reasons to consider lower ef-
ficiencies for the ST and ES processes. This is motivated
by the non-spherically symmetric deposition of angular
momentum during the 3D common envelope phase. The
20. 20 Shiber et al.
10 5
10 2
101
X
1H
4He
1016
1019
j
(
cm
2
s
1
)
Relaxed
Input
0.00 0.25 0.50 0.75 1.00
q
108
109
S
(
J
K
1
mol
1
)
10 14 10 11 10 8 10 5 10 2 101 104
Density (g cm 3)
103
104
105
106
107
108
109
Temperature
(
K
)
He-Burning
C-Burning
e-degeneracy
Octo-Tiger
MESA Primary
MESA Post-Merger
Figure 16. A comparison of the inputs from Octo-Tiger to the relaxed output of MESA. The left panels show the input
and relaxed profiles of the H and He composition (top), angular momentum (middle), and entropy (bottom). The x-axis ”q” is
the normalized exterior mass coordinate, namely, q = 0 is the star’s surface and q = 1 is the star’s center. The interface in the
entropy between the MESA and Octo-Tiger initial models occurs at q = 0.5. The panel on the right shows the Temperature-
Density diagram for the Octo-Tiger post-merger, the primary star from MESA, and the relaxed output from MESA.
Model ST SH GSF ES SSI vsurf (km/s) ϵC ϵN ϵO tcool (years)
1 1 1 1 1 1 0.036 8.48 8.62 8.90 14700
2 0 1 1 1 1 0.29 8.46 8.74 8.89 17400
3 1 1 1 0 1 0.041 8.48 8.63 8.90 14900
4 0.1 1 1 0.1 1 0.063 8.48 8.65 8.90 14800
5 0.01 1 1 0.01 1 0.12 8.48 8.64 8.90 14600
6 0.001 1 1 0.001 1 0.23 8.48 8.65 8.90 14500
7 10−7
1 1 10−7
1 1.9 8.48 8.65 8.90 25600
8 0 1 1 0 1 5.8 8.32 8.55 8.74 22200
BG 5-15 8.25-8.55 8.45-8.75 8.65-8.95
Table 1. A summary of our model parameters and results for eight different models. BG refers to observed surface values of
Betelgeuse taken from Kervella et al. (2018) and Lambert et al. (1984). Columns 2 through 6 are the efficiency factors used for
each diffusion mechanism. vsurf is the equatorial surface velocity as calculated in MESA averaged over the time spent in the
HR diagram box. ϵi is the surface value of element i calculated with Equation 2. tcool is the number of years it takes for the
star to cool from 5000K to 4000K (yellow to red in color).
high rotation is mainly concentrated around the equa-
tor and not evenly distributed in the azimuthal layers of
the model, thereby reducing the effectiveness of the ES
mechanism. In addition, as we discussed earlier, the ar-
tificial driving by angular momentum extraction during
the pre-merger phase in Octo-Tiger may lead to an
under-estimate of the actual angular momentum that
would have been deposited due to drag forces driving
the in-spiraling phase alone. These uncertainties justify
our choice of lower efficiencies for the ES and ST mecha-
nisms. However, more comprehensive and computation-
ally intensive 3D numerical simulations are necessary to
accurately quantify these effects over time.
After the relaxation, the post-merger first goes
through a contraction phase as it settles from the initial
structure of the merger. This contraction phase lasts un-
til the core becomes hot enough for He-burning, on the
order of 104
years. The evolution we are interested in
and that we show in Figure 17 is during the He-burning
phase and later, which takes place for another 106
years
and is indicated by the solid lines in Figure 17.
During these 106
years, the star evolves into the box
representing the observed surface temperature and lumi-
nosity range of Betelgeuse. We additionally plot black
dots placed 10,000 years apart and starting roughly
30,000 years before the model enters this box, for models
4 and 8 (see Table 1). This illustrates the star’s color
evolution, as there are some indications, according to
historical records, that Betelgeuse has evolved rapidly
in color (Neuhäuser et al. 2022). We also list the time,
21. Betelgeuse as a merger 21
104 3×103
4×103
6×103
2×104
Temperature (K)
105
6×104
2×105
Luminosity
(
L
)
Model 4 (10 1)
Model 5 (10 2)
Model 6 (10 3)
Model 7 (10 7)
Model 8 (0)
Figure 17. HR diagram for Models 4-8, which use smaller
diffusion coefficients for the ST and ES mechanisms. The
black dots are placed approximately 10,000 years apart start-
ing roughly 30,000 years before the model enters the observed
effective temperature range for Betelgeuse. The values in the
parentheses are the coefficients for ES and ST mechanisms.
The box represents the observed range of effective tempera-
ture and luminosity of Betelgeuse.
tcool, which takes for each model to change its effec-
tive temperature from 5000K to 4000K in Table 1. We
find a slower color evolution of several 10,000 years com-
pared to the suggested fast evolution of two millennia by
Neuhäuser et al. (2022).
We further analyze the surface composition and ro-
tation rate of our models. The surface composition is
calculated using the standard equation (see, for exam-
ple Asplund et al. 2009):
ϵi = log(Xi/XHµi) + 12 (2)
In order to compare our results to the observations of
Betelgeuse, we plot the evolution of the surface compo-
sition and velocity and use a box that represents the
target values from observations. The top and bottom
edges of the box represent the range of acceptable val-
ues from observations taken from Lambert et al. (1984),
while the left and right edges represent the time that the
model spends with a surface temperature and luminos-
ity matching Betelgeuse. This analysis is demonstrated
in Figure 18.
We can see from the upper left panel that the surface
rotational velocity decreases rapidly by nearly three or-
ders of magnitude. The primary reason for such a de-
crease in surface rotation is the diffusion of angular mo-
mentum towards the core. We note that the strongest
contributors are specifically the ST and ES diffusion co-
efficients with ST being about an order of magnitude
stronger as demonstrated in Table 1 by comparing Mod-
els 2 and 3.
After identifying the two biggest contributors to the
loss of surface rotation, we ran Models 4-8 in order to
explore the effects of decreasing the efficiency of ST and
ES diffusion. The results of this experiment are shown
in Figure 18. We note that while the range of efficiency
factors we explored do not have a significant effect on
the surface composition, the less efficient diffusion of
angular momentum is critical to the evolution of the
surface rotation. We find for our models, we do not see
a sufficiently fast rotation rate unless the efficiency is
reduced down to ∼ 10-7
or more of the default value of
1.0. We also note that as the efficiency is reduced and
angular momentum cannot diffuse towards the core as
rapidly, the model becomes more unstable during the
contraction phase.
4. SUMMARY AND DISCUSSION
This paper presents an attempt to model the complete
evolution of a binary star merger, spanning from the
onset of the interaction to the common envelope phase,
tidal disruption phase, and subsequent aftermath. Our
study focuses on the merger between a 16 M⊙ primary
star and a 4 M⊙ secondary star during the post-main
sequence evolution of the primary towards the RSG
branch. The common envelope phase occurs when the
primary’s expanding envelope comes into contact with
the secondary, leading to the decay of the secondary’s
orbit within the primary’s extended envelope. The sec-
ondary star merges with the He core of the primary,
resulting in a mergeburst transient phase and the ejec-
tion of approximately 0.6 M⊙ of material in a bipolar
outflow.
To conduct this study, we employed various methods
and numerical techniques, including 3D hydrodynami-
cal simulations with the Octo-Tiger code and nuclear
evolution modeling with the MESA code. The transi-
tion between the two codes posed challenges due to dif-
ferences in assumptions, such as the equation of state,
treatment of nuclear burning, and inclusion of radiation
effects. The 3D Octo-Tiger simulation required sig-
nificant resolution (to ensure that the structures of both
the primary and secondary stars are adequately resolved
for dynamical stability) and a large simulation box (to
allow for the tracking of the merger-induced mass-loss in
order to investigate the properties of the unbound ma-
terial). Finally, to facilitate a reasonable computation
time, we drove the merger by removing angular momen-
tum from the orbit at a low rate of 1% per (initial)
orbital period.
Despite the limitations in our approach, we success-
fully achieved our main goal of studying the post-merger
evolution and comparing it to observations of stars with
22. 22 Shiber et al.
10 1
100
101
102
Surface
Velocity
(
km
s
1
)
vsurf
8.0
8.2
8.4
8.6
8.8
9.0
C
C
105 106
Star Age (Years)
8.0
8.2
8.4
8.6
8.8
9.0
N
N
Model 4 (10 1)
Model 5 (10 2)
Model 6 (10 3)
Model 7 (10 7)
Model 8 (0)
105 106
Star Age (Years)
8.0
8.2
8.4
8.6
8.8
9.0
O
O
Figure 18. Evolution of the post merger object for five MESA runs with different rotation mixing coefficients: 0 (magenta),
10−7
(red), 10−3
(green), 10−2
(orange), and 10−1
(blue). Plotted are (from top left to bottom right): surface equatorial
rotational velocity in km/s, Carbon, Nitrogen, and Oxygen solar scaled surface abundances. The dashed black square frames
the time when the models are within the 3σ error bars of the observed luminosity and effective temperature of Betelgeuse (on
the x-axis) and the observed Betelgeuse ranges (on the y-axis).
peculiar envelope properties, such as Betelgeuse. Key
findings of our study include the following:
• During the common envelope phase, which lasts
for 340 days after contact at 50 R⊙, the in-spiral of
the secondary into the primary’s envelope results
in significant angular momentum deposition along
the equatorial plane (Figure 15).
• Due to resolution limitations, we couldn’t investi-
gate the details of the secondary’s tidal disrup-
tion, stream-core interaction, and the potential
rejuvenation of the primary. However, based on
the mass ratio studied (q = 0.25), we assume
a “quiet merger” scenario (Chatzopoulos et al.
2020), where the post-merger star continues to
evolve toward the RSG phase.
• The dynamical merger leads to the ejection of ap-
proximately 0.6 M⊙ of material at velocities of
200-300 km/s, characteristic of mergeburst events
(see Figures 9 and 10, respectively). Interest-
ingly, 1/3 of this unbound gas originated from
the spiralling-in secondary star (Figure 9). The
unbound gas exhibits a distinct bipolar geometry
with most of its mass concentrated in two clumpy
rings (Figure 11).
• If the post-merger star explodes as a Type IIP su-
pernova within the next 50,000 to 500,000 years,
the circumstellar material formed by the previous
merger would be located at a distance of 1 − 100
pc, depending on the specific modeling of wind in-
teraction (Figure 13). The densities of this mate-
rial are unlikely to significantly affect the radiative
properties of the supernova.
• The long-term nuclear evolution of the post-
merger star is consistent with the well-known RSG
23. Betelgeuse as a merger 23
star Betelgeuse, as evidenced by the observed sur-
face enhancement of 14
N (see Figure 18) and its
location in the HR diagram (see Figure 17).
• The long-term surface rotation rate of the post-
merger star depends on the efficiency of angu-
lar momentum transport mechanisms in the 1D
evolution calculation (Figure 18). Rapidly spin-
ning post-mergers are found when the efficiency
of meridional circulation (Eddington-Sweet mech-
anism) is low and magnetically-driven angular
momentum transport (Spruit-Taylor mechanism)
is minimal (see Table 1). We argue that the
anisotropic deposition of angular momentum con-
centrated along the equatorial plane in a merger
scenario suggests low efficiency of inward angu-
lar momentum transport. Other factors influenc-
ing the surface rotation rate include the angu-
lar momentum carried away by mass loss during
the merger and post-merger evolution, as well as
the underestimation of the total angular momen-
tum deposited in the primary envelope due to our
merger driving method. Additionally, the limited
size of the primary’s envelope expansion up to a ra-
dius of 50 R⊙ restricts the number of secondary or-
bits during the common envelope phase and, con-
sequently, the spin-up potential. Previous studies
have shown that contact at higher radii (100-500
R⊙) can lead to higher post-merger spin-up rates
(Chatzopoulos et al. 2020).
Our results shed light on the post-merger evolution
and provide valuable insights into the properties of
merger events and their impact on stellar evolution.
However, further improvements are necessary, includ-
ing refining the codes and techniques used, investigating
the details of the tidal disruption and stream-core inter-
action, and addressing uncertainties related to angular
momentum transport and mass loss during the merger
and post-merger phases.
Moving forward, our future work will focus on en-
hancing the Octo-Tiger code, incorporating a more
suitable equation of state and radiation effects, and ex-
ploring the interaction between supernovae and merger-
driven circumstellar environments. By delving deeper
into the physics of stellar mergers, we aim to advance
our understanding of massive star evolution, the prop-
erties of supernova progenitors, and the role of mergers
in shaping the astrophysical transient landscape.
ACKNOWLEDGMENTS
We are grateful to Athira Menon and Craig Wheeler
for discussions on Betelgeuse and SN1987A-like pro-
genitors. We also thank Geoffrey Clayton, Dominic
Marcello, and Orsola De Marco for useful feedback
and discussions. The research of EC was supported
by the Department of Energy Early Career Award
DE-SC0021228. The numerical work was carried
out using the computational resources (QueenBee2) of
the Louisiana Optical Network Initiative (LONI) and
Louisiana State University’s High Performance Com-
puting (LSU HPC). Our use of BigRed3 at Indiana
University was supported by Lilly Endowment, Inc.,
through its support for the Indiana University Perva-
sive Technology Institute. This work also required the
use and integration of a Python package for astronomy,
yt (http://yt-project.org, Turk et al. 2011).
SUPPLEMENTARY MATERIALS
Octo-Tiger is available on GitHub2
and was built
using the following build chain3
. On Queen-Bee and Bi-
gRed Octo-Tiger version Marcello et al. (2021) was
used. All necessary files to reproduce the Betelgeuse
post-merger evolution in MESA are available on Zen-
odo4
.
Software: Octo-Tiger (Marcello et al. 2021),
MESA-r21.12.1 (Paxton et al. 2011, 2013, 2015, 2018,
2019), Python (available from python.org), Matplotlib
(Hunter 2007), Numpy (van der Walt et al. 2011), yt
(Turk et al. 2011)
2 https://github.com/STEllAR-GROUP/octotiger
3 https://github.com/STEllAR-GROUP/OctoTigerBuildChain
4 https://doi.org/10.5281/zenodo.8422498
24. 24 Shiber et al.
REFERENCES
Asplund, M., Grevesse, N., Sauval, A. J., Scott, P. 2009,
ARAA, 47, 481,
doi: 10.1146/annurev.astro.46.060407.145222
Bodenheimer, P., Taam, R. E. 1984, ApJ, 280, 771,
doi: 10.1086/162049
Bonnell, I. A., Bate, M. R. 2005, MNRAS, 362, 915,
doi: 10.1111/j.1365-2966.2005.09360.x
Chamandy, L., Frank, A., Blackman, E. G., et al. 2018,
MNRAS, 480, 1898, doi: 10.1093/mnras/sty1950
Chatzopoulos, E., Frank, J., Marcello, D. C., Clayton,
G. C. 2020, ApJ, 896, 50, doi: 10.3847/1538-4357/ab91bb
Chatzopoulos, E., Wheeler, J. C., Vinko, J. 2012, ApJ,
746, 121, doi: 10.1088/0004-637X/746/2/121
Chevalier, R. A. 1982, ApJ, 258, 790, doi: 10.1086/160126
Chevalier, R. A., Fransson, C. 1994, ApJ, 420, 268,
doi: 10.1086/173557
Corradi, R. L. M., Sabin, L., Miszalski, B., et al. 2011,
MNRAS, 410, 1349,
doi: 10.1111/j.1365-2966.2010.17523.x
Costa, A. D., Canto Martins, B. L., Bravo, J. P., et al.
2015, ApJL, 807, L21, doi: 10.1088/2041-8205/807/2/L21
Cox, J. P., Giuli, R. T. 1968, Principles of stellar
structure (Gordon and Breach)
de Jager, C., Nieuwenhuijzen, H., van der Hucht, K. A.
1988, AAS, 72, 259
de Mink, S. E., Langer, N., Izzard, R. G., Sana, H., de
Koter, A. 2013, ApJ, 764, 166,
doi: 10.1088/0004-637X/764/2/166
de Mink, S. E., Sana, H., Langer, N., Izzard, R. G.,
Schneider, F. R. N. 2014, ApJ, 782, 7,
doi: 10.1088/0004-637X/782/1/7
Dunstall, P. R., Dufton, P. L., Sana, H., et al. 2015, AA,
580, A93, doi: 10.1051/0004-6361/201526192
Gilliland, R. L., Dupree, A. K. 1996, ApJL, 463, L29,
doi: 10.1086/310043
Heger, A., Langer, N., Woosley, S. E. 2000, ApJ, 528,
368, doi: 10.1086/308158
Heger, A., Woosley, S. E., Spruit, H. C. 2005, ApJ, 626,
350, doi: 10.1086/429868
Hunter, J. D. 2007, Computing in Science and Engineering,
9, 90, doi: 10.1109/MCSE.2007.55
Iaconi, R., Reichardt, T., Staff, J., et al. 2017, MNRAS,
464, 4028, doi: 10.1093/mnras/stw2377
Ivanova, N. 2002, PhD thesis, University of Oxford
Ivanova, N., Podsiadlowski, P. 2002, ApSS, 281, 191,
doi: 10.1023/A:1019553109023
Ivanova, N., Podsiadlowski, P. 2003, in From Twilight to
Highlight: The Physics of Supernovae, ed. W. Hillebrandt
B. Leibundgut, 19, doi: 10.1007/10828549 3
Ivanova, N., Podsiadlowski, P., Spruit, H. 2002, MNRAS,
334, 819, doi: 10.1046/j.1365-8711.2002.05543.x
Jadlovský, D., Krtička, J., Paunzen, E., Štefl, V. 2023,
NewA, 99, 101962, doi: 10.1016/j.newast.2022.101962
Kadam, K., Motl, P. M., Marcello, D. C., Frank, J.,
Clayton, G. C. 2018, MNRAS, 481, 3683,
doi: 10.1093/mnras/sty2540
Kervella, P., Decin, L., Richards, A. M. S., et al. 2018,
AA, 609, A67, doi: 10.1051/0004-6361/201731761
Klencki, J., Nelemans, G., Istrate, A. G., Chruslinska, M.
2021, AA, 645, A54, doi: 10.1051/0004-6361/202038707
Lambert, D. L., Brown, J. A., Hinkle, K. H., Johnson,
H. R. 1984, ApJ, 284, 223, doi: 10.1086/162401
Lau, M. Y. M., Hirai, R., González-Bolı́var, M., et al.
2022a, MNRAS, 512, 5462, doi: 10.1093/mnras/stac049
Lau, M. Y. M., Hirai, R., Price, D. J., Mandel, I. 2022b,
MNRAS, 516, 4669, doi: 10.1093/mnras/stac2490
López Ariste, A., Mathias, P., Tessore, B., et al. 2018,
AA, 620, A199, doi: 10.1051/0004-6361/201834178
López-Cámara, D., De Colle, F., Moreno Méndez, E.,
Shiber, S., Iaconi, R. 2022, MNRAS, 513, 3634,
doi: 10.1093/mnras/stac932
Maeder, A., Zahn, J.-P. 1998, AA, 334, 1000
Marcello, D., Daiß, G., Amini, P., et al. 2021,
STEllAR-GROUP/octotiger: Benchmark paper, v0.8.0,
Zenodo, doi: 10.5281/zenodo.4432574
Marcello, D. C., Shiber, S., De Marco, O., et al. 2021,
MNRAS, 504, 5345, doi: 10.1093/mnras/stab937
Mason, B. D., Hartkopf, W. I., Gies, D. R., Henry, T. J.,
Helsel, J. W. 2009, AJ, 137, 3358,
doi: 10.1088/0004-6256/137/2/3358
Menon, A., Heger, A. 2017, MNRAS, 469, 4649.
https://arxiv.org/abs/1703.04918
Menon, A., Utrobin, V., Heger, A. 2019, MNRAS, 482,
438, doi: 10.1093/mnras/sty2647
Moreno, M. M., Schneider, F. R. N., Röpke, F. K., et al.
2022, AA, 667, A72, doi: 10.1051/0004-6361/202142731
Neuhäuser, R., Torres, G., Mugrauer, M., et al. 2022,
MNRAS, 516, 693, doi: 10.1093/mnras/stac1969
Passy, J.-C., De Marco, O., Fryer, C. L., et al. 2012, ApJ,
744, 52, doi: 10.1088/0004-637X/744/1/52
Paxton, B., Bildsten, L., Dotter, A., et al. 2011, ApJS, 192,
3, doi: 10.1088/0067-0049/192/1/3
Paxton, B., Cantiello, M., Arras, P., et al. 2013, ApJS, 208,
4, doi: 10.1088/0067-0049/208/1/4
Paxton, B., Marchant, P., Schwab, J., et al. 2015, ApJS,
220, 15, doi: 10.1088/0067-0049/220/1/15
Paxton, B., Schwab, J., Bauer, E. B., et al. 2018, ApJS,
234, 34, doi: 10.3847/1538-4365/aaa5a8
25. Betelgeuse as a merger 25
Paxton, B., Smolec, R., Schwab, J., et al. 2019, ApJS, 243,
10, doi: 10.3847/1538-4365/ab2241
Plait, P. C., Lundqvist, P., Chevalier, R. A., Kirshner,
R. P. 1995, ApJ, 439, 730, doi: 10.1086/175213
Podsiadlowski, P., Joss, P. C., Rappaport, S. 1990, AA,
227, L9
Podsiadlowski, P., Morris, T. S., Ivanova, N. 2006, in
Astronomical Society of the Pacific Conference Series,
Vol. 355, Stars with the B[e] Phenomenon, ed. M. Kraus
A. S. Miroshnichenko, 259
Pribulla, T. 1998, Contributions of the Astronomical
Observatory Skalnate Pleso, 28, 101
Reichardt, T. A., De Marco, O., Iaconi, R., Tout, C. A.,
Price, D. J. 2019, MNRAS, 484, 631,
doi: 10.1093/mnras/sty3485
Renzo, M., Zapartas, E., de Mink, S. E., et al. 2019, AA,
624, A66, doi: 10.1051/0004-6361/201833297
Ricker, P. M., Timmes, F. X., Taam, R. E., Webbink,
R. F. 2019, IAU Symposium, 346, 449,
doi: 10.1017/S1743921318007433
Sana, H., de Mink, S. E., de Koter, A., et al. 2012, Science,
337, 444, doi: 10.1126/science.1223344
Sand, C., Ohlmann, S. T., Schneider, F. R. N., Pakmor, R.,
Röpke, F. K. 2020, AA, 644, A60,
doi: 10.1051/0004-6361/202038992
Savitzky, A., Golay, M. J. 1964, Analytical chemistry, 36,
1627
Schneider, F. R. N., Podsiadlowski, P., Langer, N., Castro,
N., Fossati, L. 2016, MNRAS, 457, 2355,
doi: 10.1093/mnras/stw148
Schreier, R., Hillel, S., Shiber, S., Soker, N. 2021,
MNRAS, 508, 2386, doi: 10.1093/mnras/stab2687
Shiber, S., Iaconi, R., De Marco, O., Soker, N. 2019,
MNRAS, 488, 5615, doi: 10.1093/mnras/stz2013
Shiber, S., Schreier, R., Soker, N. 2016, Research in
Astronomy and Astrophysics, 16, 117,
doi: 10.1088/1674-4527/16/7/117
Shiber, S., Soker, N. 2018, MNRAS, 477, 2584,
doi: 10.1093/mnras/sty843
Smith, N., Ferland, G. J. 2007, ApJ, 655, 911,
doi: 10.1086/510328
Soker, N. 2015, ApJ, 800, 114,
doi: 10.1088/0004-637X/800/2/114
Soker, N., Tylenda, R. 2006, MNRAS, 373, 733,
doi: 10.1111/j.1365-2966.2006.11056.x
Sullivan, J. M., Nance, S., Wheeler, J. C. 2020, ApJ, 905,
128, doi: 10.3847/1538-4357/abc3c9
Taam, R. E., Bodenheimer, P. 1991, ApJ, 373, 246,
doi: 10.1086/170043
Terman, J. L., Taam, R. E., Hernquist, L. 1994, ApJ,
422, 729, doi: 10.1086/173765
Turk, M. J., Smith, B. D., Oishi, J. S., et al. 2011, ApJ,
192, 9, doi: 10.1088/0067-0049/192/1/9
Uitenbroek, H., Dupree, A. K., Gilliland, R. L. 1998, AJ,
116, 2501, doi: 10.1086/300596
van der Walt, S., Colbert, S. C., Varoquaux, G. 2011,
Computing in Science and Engineering, 13, 22,
doi: 10.1109/MCSE.2011.37
Vink, J. S., de Koter, A., Lamers, H. J. G. L. M. 2001,
AA, 369, 574, doi: 10.1051/0004-6361:20010127
Wheeler, J. C., Chatzopoulos, E. 2023, Astronomy and
Geophysics, 64, 3.11, doi: 10.1093/astrogeo/atad020
Wheeler, J. C., Nance, S., Diaz, M., et al. 2017, MNRAS,
465, 2654, doi: 10.1093/mnras/stw2893
Zahn, J. P. 1992, AA, 265, 115