1) The document analyzes 72 galaxy cluster collisions observed with Hubble and Chandra telescopes to test theories of non-gravitational dark matter interactions.
2) It detects the existence of dark matter at 7.6 sigma significance by comparing the positions of dark mass concentrations to stars and gas.
3) Combining measurements from all collisions, it constrains the dark matter self-interaction cross-section to be less than 0.47 cm^2/g (95% confidence level), ruling out some proposed dark matter models with stronger interactions.
End point of_black_ring_instabilities_and_the_weak_cosmic_censorship_conjectureSérgio Sacani
We produce the first concrete evidence that violation of the weak cosmic censorship conjecture can occur
in asymptotically flat spaces of five dimensions by numerically evolving perturbed black rings. For certain
thin rings, we identify a new, elastic-type instability dominating the evolution, causing the system to settle to
a spherical black hole. However, for sufficiently thin rings the Gregory-Laflamme mode is dominant, and the
instability unfolds similarly to that of black strings, where the horizon develops a structure of bulges connected
by necks which become ever thinner over time.
Large scale mass_distribution_in_the_illustris_simulationSérgio Sacani
Observations at low redshifts thus far fail to account for all of the baryons expected in the
Universe according to cosmological constraints. A large fraction of the baryons presumably
resides in a thin and warm–hot medium between the galaxies, where they are difficult to observe
due to their low densities and high temperatures. Cosmological simulations of structure
formation can be used to verify this picture and provide quantitative predictions for the distribution
of mass in different large-scale structure components. Here we study the distribution
of baryons and dark matter at different epochs using data from the Illustris simulation. We
identify regions of different dark matter density with the primary constituents of large-scale
structure, allowing us to measure mass and volume of haloes, filaments and voids. At redshift
zero, we find that 49 per cent of the dark matter and 23 per cent of the baryons are within
haloes more massive than the resolution limit of 2 × 108 M⊙. The filaments of the cosmic
web host a further 45 per cent of the dark matter and 46 per cent of the baryons. The remaining
31 per cent of the baryons reside in voids. The majority of these baryons have been transported
there through active galactic nuclei feedback. We note that the feedback model of Illustris
is too strong for heavy haloes, therefore it is likely that we are overestimating this amount.
Categorizing the baryons according to their density and temperature, we find that 17.8 per cent
of them are in a condensed state, 21.6 per cent are present as cold, diffuse gas, and 53.9 per cent
are found in the state of a warm–hot intergalactic medium.
End point of_black_ring_instabilities_and_the_weak_cosmic_censorship_conjectureSérgio Sacani
We produce the first concrete evidence that violation of the weak cosmic censorship conjecture can occur
in asymptotically flat spaces of five dimensions by numerically evolving perturbed black rings. For certain
thin rings, we identify a new, elastic-type instability dominating the evolution, causing the system to settle to
a spherical black hole. However, for sufficiently thin rings the Gregory-Laflamme mode is dominant, and the
instability unfolds similarly to that of black strings, where the horizon develops a structure of bulges connected
by necks which become ever thinner over time.
Large scale mass_distribution_in_the_illustris_simulationSérgio Sacani
Observations at low redshifts thus far fail to account for all of the baryons expected in the
Universe according to cosmological constraints. A large fraction of the baryons presumably
resides in a thin and warm–hot medium between the galaxies, where they are difficult to observe
due to their low densities and high temperatures. Cosmological simulations of structure
formation can be used to verify this picture and provide quantitative predictions for the distribution
of mass in different large-scale structure components. Here we study the distribution
of baryons and dark matter at different epochs using data from the Illustris simulation. We
identify regions of different dark matter density with the primary constituents of large-scale
structure, allowing us to measure mass and volume of haloes, filaments and voids. At redshift
zero, we find that 49 per cent of the dark matter and 23 per cent of the baryons are within
haloes more massive than the resolution limit of 2 × 108 M⊙. The filaments of the cosmic
web host a further 45 per cent of the dark matter and 46 per cent of the baryons. The remaining
31 per cent of the baryons reside in voids. The majority of these baryons have been transported
there through active galactic nuclei feedback. We note that the feedback model of Illustris
is too strong for heavy haloes, therefore it is likely that we are overestimating this amount.
Categorizing the baryons according to their density and temperature, we find that 17.8 per cent
of them are in a condensed state, 21.6 per cent are present as cold, diffuse gas, and 53.9 per cent
are found in the state of a warm–hot intergalactic medium.
The characterization of_the_gamma_ray_signal_from_the_central_milk_way_a_comp...Sérgio Sacani
Past studies have identified a spatially extended excess of ∼1-3 GeV gamma rays from the region
surrounding the Galactic Center, consistent with the emission expected from annihilating dark
matter. We revisit and scrutinize this signal with the intention of further constraining its characteristics
and origin. By applying cuts to the Fermi event parameter CTBCORE, we suppress the tails
of the point spread function and generate high resolution gamma-ray maps, enabling us to more
easily separate the various gamma-ray components. Within these maps, we find the GeV excess
to be robust and highly statistically significant, with a spectrum, angular distribution, and overall
normalization that is in good agreement with that predicted by simple annihilating dark matter
models. For example, the signal is very well fit by a 36-51 GeV dark matter particle annihilating to
b
¯b with an annihilation cross section of σv = (1−3)×10−26 cm3
/s (normalized to a local dark matter
density of 0.4 GeV/cm3
). Furthermore, we confirm that the angular distribution of the excess is
approximately spherically symmetric and centered around the dynamical center of the Milky Way
(within ∼0.05◦
of Sgr A∗
), showing no sign of elongation along the Galactic Plane. The signal is
observed to extend to at least ' 10◦
from the Galactic Center, disfavoring the possibility that this
emission originates from millisecond pulsars.
Effect of Rotation on a Layer of Micro-Polar Ferromagnetic Dusty Fluid Heated...IJERA Editor
This paper deals with the theoretical investigation of effect of rotation on micro-polar ferromagnetic dusty fluid
layer heated from below in a porous medium. Linear stability analysis and normal mode analysis methods are
used to find an exact solution for a flat micro-polar ferromagnetic fluid layer contained between two free
boundaries . In case of stationary convection, the effect of various parameters like medium permeability
parameter, non-buoyancy magnetization parameter, micro-polar coupling parameter, spin-diffusion parameter,
micro-polar heat conduction parameter, dust particles parameter and rotation parameter has been analyzed and
results are depicted graphically. In the absence of dust particles, rotation, micro-viscous effect and micro-inertia,
the sufficient condition is obtained for non-oscillatory modes
We present long-baseline Atacama Large Millimeter/submillimeter Array (ALMA) observations of
the 870 m continuum emission from the nearest gas-rich protoplanetary disk, around TW Hya, that
trace millimeter-sized particles down to spatial scales as small as 1 AU (20 mas). These data reveal
a series of concentric ring-shaped substructures in the form of bright zones and narrow dark annuli
(1{6AU) with modest contrasts (5{30%). We associate these features with concentrations of solids
that have had their inward radial drift slowed or stopped, presumably at local gas pressure maxima.
No signicant non-axisymmetric structures are detected. Some of the observed features occur near
temperatures that may be associated with the condensation fronts of major volatile species, but the
relatively small brightness contrasts may also be a consequence of magnetized disk evolution (the
so-called zonal
ows). Other features, particularly a narrow dark annulus located only 1 AU from the
star, could indicate interactions between the disk and young planets. These data signal that ordered
substructures on AU scales can be common, fundamental factors in disk evolution, and that high
resolution microwave imaging can help characterize them during the epoch of planet formation.
Keywords: protoplanetary disks | planet-disk interactions | stars: individual (TW Hydrae)
Millimetre-wave emission from an intermediatemass black hole candidate in the...Sérgio Sacani
It is widely accepted that black holes with masses greater
than a million solar masses (M⊙) lurk at the centres of massive
galaxies. The origins of such ‘supermassive’ black holes
(SMBHs) remain unknown1, although those of stellar-mass
black holes are well understood. One possible scenario is that
intermediate-mass black holes (IMBHs), which are formed
by the runaway coalescence of stars in young compact star
clusters2, merge at the centre of a galaxy to form a SMBH3.
Although many candidates for IMBHs have been proposed,
none is accepted as definitive. Recently, we discovered a
peculiar molecular cloud, CO–0.40–0.22, with an extremely
broad velocity width, near the centre of our Milky Way galaxy.
Based on the careful analysis of gas kinematics, we concluded
that a compact object with a mass of about 105M⊙ is lurking
in this cloud4. Here we report the detection of a point-like
continuum source as well as a compact gas clump near the
centre of CO–0.40–0.22. This point-like continuum source
(CO–0.40–0.22*) has a wide-band spectrum consistent with
1/500 of the Galactic SMBH (Sgr A*) in luminosity. Numerical
simulations around a point-like massive object reproduce the
kinematics of dense molecular gas well, which suggests that
CO–0.40–0.22* is one of the most promising candidates for
an intermediate-mass black hole.
A Study of Some Optical Properties of Chromic Chloride(퐂퐫퐂퐥ퟑ )Thin FilmQUESTJOURNAL
ABSTRACT: In this work,the optical properties of chromic chloride(푪풓푪풍ퟑ )thin film prepared at different thickness has been measured. The relationship between transparency, absorbance and photon energy for the prepared samples has been studied. It has been found, the behavior of curves is the same for each samples.Moreover, it has been observed thatThe best fit of theexperimental curve to a band gap function was obtained for 푛 = 2 to direct bandgap energy values the obtained values are 1.531 eV, 1.533 eV,1.536 eV, and 1.539 eV for dip the rated of 퐶푙 (0.0 - 0.25 – 0.50 and 0.75 ) respectively.
Young remmants of_type_ia_supernovae_and_their_progenitors_a_study_of_snr_g19_03Sérgio Sacani
Type Ia supernovae, with their remarkably homogeneous light curves and spectra, have been used as
standardizable candles to measure the accelerating expansion of the Universe. Yet, their progenitors
remain elusive. Common explanations invoke a degenerate star (white dwarf) which explodes upon
reaching close to the Chandrasekhar limit, by either steadily accreting mass from a companion star
or violently merging with another degenerate star. We show that circumstellar interaction in young
Galactic supernova remnants can be used to distinguish between these single and double degenerate
progenitor scenarios. Here we propose a new diagnostic, the Surface Brightness Index, which can
be computed from theory and compared with Chandra and VLA observations. We use this method
to demonstrate that a double degenerate progenitor can explain the decades-long
ux rise and size
increase of the youngest known Galactic SNR G1.9+0.3. We disfavor a single degenerate scenario.
We attribute the observed properties to the interaction between a steep ejecta prole and a constant
density environment. We suggest using the upgraded VLA to detect circumstellar interaction in
the remnants of historical Type Ia supernovae in the Local Group of galaxies. This may settle the
long-standing debate over their progenitors.
Subject headings: ISM: supernova remnants | radio continuum: general | X-rays: general | bi-
naries: general | circumstellar matter | supernovae: general | ISM: individual
objects(SNR G1.9+0.3)
Virtual particles in the vacuum and gravityEran Sinbar
Heisenberg’s uncertainty principle in energy and time, comes in the form of virtual particle pairs in empty space. These virtual pairs of matter and anti-matter in empty space pop in and out of existence. Their short existence can be measured directly through the Casimir effect [1]. These virtual particles constitute the Hawking radiation. They carry the latent black hole information from the surface of the event horizon into the void of space during the evaporation process of the black hole[2],[3].In this article I suggest a model in which these virtual particles in the vacuum are the source for gravity, curvature of space and time dilation.
Understanding the experimental and mathematical derivation of Heisenberg's Uncertainty Principle. Simple application for estimating single degree of freedom particle in a potential free environment is also discussed.
Old supernova dust_factory_revealed_at_galactic_centerSérgio Sacani
Artigo descreve como os astrônomos usando o SOFIA detectaram uma fábrica de poeira perto de uma supernova no centro da Via Láctea. Um resultado importante para se entender cada vez mais sobre a evolução das galáxias.
The characterization of_the_gamma_ray_signal_from_the_central_milk_way_a_comp...Sérgio Sacani
Past studies have identified a spatially extended excess of ∼1-3 GeV gamma rays from the region
surrounding the Galactic Center, consistent with the emission expected from annihilating dark
matter. We revisit and scrutinize this signal with the intention of further constraining its characteristics
and origin. By applying cuts to the Fermi event parameter CTBCORE, we suppress the tails
of the point spread function and generate high resolution gamma-ray maps, enabling us to more
easily separate the various gamma-ray components. Within these maps, we find the GeV excess
to be robust and highly statistically significant, with a spectrum, angular distribution, and overall
normalization that is in good agreement with that predicted by simple annihilating dark matter
models. For example, the signal is very well fit by a 36-51 GeV dark matter particle annihilating to
b
¯b with an annihilation cross section of σv = (1−3)×10−26 cm3
/s (normalized to a local dark matter
density of 0.4 GeV/cm3
). Furthermore, we confirm that the angular distribution of the excess is
approximately spherically symmetric and centered around the dynamical center of the Milky Way
(within ∼0.05◦
of Sgr A∗
), showing no sign of elongation along the Galactic Plane. The signal is
observed to extend to at least ' 10◦
from the Galactic Center, disfavoring the possibility that this
emission originates from millisecond pulsars.
Effect of Rotation on a Layer of Micro-Polar Ferromagnetic Dusty Fluid Heated...IJERA Editor
This paper deals with the theoretical investigation of effect of rotation on micro-polar ferromagnetic dusty fluid
layer heated from below in a porous medium. Linear stability analysis and normal mode analysis methods are
used to find an exact solution for a flat micro-polar ferromagnetic fluid layer contained between two free
boundaries . In case of stationary convection, the effect of various parameters like medium permeability
parameter, non-buoyancy magnetization parameter, micro-polar coupling parameter, spin-diffusion parameter,
micro-polar heat conduction parameter, dust particles parameter and rotation parameter has been analyzed and
results are depicted graphically. In the absence of dust particles, rotation, micro-viscous effect and micro-inertia,
the sufficient condition is obtained for non-oscillatory modes
We present long-baseline Atacama Large Millimeter/submillimeter Array (ALMA) observations of
the 870 m continuum emission from the nearest gas-rich protoplanetary disk, around TW Hya, that
trace millimeter-sized particles down to spatial scales as small as 1 AU (20 mas). These data reveal
a series of concentric ring-shaped substructures in the form of bright zones and narrow dark annuli
(1{6AU) with modest contrasts (5{30%). We associate these features with concentrations of solids
that have had their inward radial drift slowed or stopped, presumably at local gas pressure maxima.
No signicant non-axisymmetric structures are detected. Some of the observed features occur near
temperatures that may be associated with the condensation fronts of major volatile species, but the
relatively small brightness contrasts may also be a consequence of magnetized disk evolution (the
so-called zonal
ows). Other features, particularly a narrow dark annulus located only 1 AU from the
star, could indicate interactions between the disk and young planets. These data signal that ordered
substructures on AU scales can be common, fundamental factors in disk evolution, and that high
resolution microwave imaging can help characterize them during the epoch of planet formation.
Keywords: protoplanetary disks | planet-disk interactions | stars: individual (TW Hydrae)
Millimetre-wave emission from an intermediatemass black hole candidate in the...Sérgio Sacani
It is widely accepted that black holes with masses greater
than a million solar masses (M⊙) lurk at the centres of massive
galaxies. The origins of such ‘supermassive’ black holes
(SMBHs) remain unknown1, although those of stellar-mass
black holes are well understood. One possible scenario is that
intermediate-mass black holes (IMBHs), which are formed
by the runaway coalescence of stars in young compact star
clusters2, merge at the centre of a galaxy to form a SMBH3.
Although many candidates for IMBHs have been proposed,
none is accepted as definitive. Recently, we discovered a
peculiar molecular cloud, CO–0.40–0.22, with an extremely
broad velocity width, near the centre of our Milky Way galaxy.
Based on the careful analysis of gas kinematics, we concluded
that a compact object with a mass of about 105M⊙ is lurking
in this cloud4. Here we report the detection of a point-like
continuum source as well as a compact gas clump near the
centre of CO–0.40–0.22. This point-like continuum source
(CO–0.40–0.22*) has a wide-band spectrum consistent with
1/500 of the Galactic SMBH (Sgr A*) in luminosity. Numerical
simulations around a point-like massive object reproduce the
kinematics of dense molecular gas well, which suggests that
CO–0.40–0.22* is one of the most promising candidates for
an intermediate-mass black hole.
A Study of Some Optical Properties of Chromic Chloride(퐂퐫퐂퐥ퟑ )Thin FilmQUESTJOURNAL
ABSTRACT: In this work,the optical properties of chromic chloride(푪풓푪풍ퟑ )thin film prepared at different thickness has been measured. The relationship between transparency, absorbance and photon energy for the prepared samples has been studied. It has been found, the behavior of curves is the same for each samples.Moreover, it has been observed thatThe best fit of theexperimental curve to a band gap function was obtained for 푛 = 2 to direct bandgap energy values the obtained values are 1.531 eV, 1.533 eV,1.536 eV, and 1.539 eV for dip the rated of 퐶푙 (0.0 - 0.25 – 0.50 and 0.75 ) respectively.
Young remmants of_type_ia_supernovae_and_their_progenitors_a_study_of_snr_g19_03Sérgio Sacani
Type Ia supernovae, with their remarkably homogeneous light curves and spectra, have been used as
standardizable candles to measure the accelerating expansion of the Universe. Yet, their progenitors
remain elusive. Common explanations invoke a degenerate star (white dwarf) which explodes upon
reaching close to the Chandrasekhar limit, by either steadily accreting mass from a companion star
or violently merging with another degenerate star. We show that circumstellar interaction in young
Galactic supernova remnants can be used to distinguish between these single and double degenerate
progenitor scenarios. Here we propose a new diagnostic, the Surface Brightness Index, which can
be computed from theory and compared with Chandra and VLA observations. We use this method
to demonstrate that a double degenerate progenitor can explain the decades-long
ux rise and size
increase of the youngest known Galactic SNR G1.9+0.3. We disfavor a single degenerate scenario.
We attribute the observed properties to the interaction between a steep ejecta prole and a constant
density environment. We suggest using the upgraded VLA to detect circumstellar interaction in
the remnants of historical Type Ia supernovae in the Local Group of galaxies. This may settle the
long-standing debate over their progenitors.
Subject headings: ISM: supernova remnants | radio continuum: general | X-rays: general | bi-
naries: general | circumstellar matter | supernovae: general | ISM: individual
objects(SNR G1.9+0.3)
Virtual particles in the vacuum and gravityEran Sinbar
Heisenberg’s uncertainty principle in energy and time, comes in the form of virtual particle pairs in empty space. These virtual pairs of matter and anti-matter in empty space pop in and out of existence. Their short existence can be measured directly through the Casimir effect [1]. These virtual particles constitute the Hawking radiation. They carry the latent black hole information from the surface of the event horizon into the void of space during the evaporation process of the black hole[2],[3].In this article I suggest a model in which these virtual particles in the vacuum are the source for gravity, curvature of space and time dilation.
Understanding the experimental and mathematical derivation of Heisenberg's Uncertainty Principle. Simple application for estimating single degree of freedom particle in a potential free environment is also discussed.
Old supernova dust_factory_revealed_at_galactic_centerSérgio Sacani
Artigo descreve como os astrônomos usando o SOFIA detectaram uma fábrica de poeira perto de uma supernova no centro da Via Láctea. Um resultado importante para se entender cada vez mais sobre a evolução das galáxias.
Saturns fast spin_determined_from_its_gravitational_field_and_oblatenessSérgio Sacani
ARtigo descreve o novo método usado para determinar com precisão o período de rotação do planeta Saturno. Uma das grandes questões da astronomia. De acordo com o artigo o período de rotação de Saturno é de 10 horas 32 minutos e 45 segundos (+/- 46 segundos).
Artigo descreve a descoberta dos astrônomos de 4 imagens de uma supernova geradas pelo efeito de lente gravitacional e formando o raro padrão da Cruz de Einstein.
Wind from the_black_hole_accretion_disk_driving_a_molecular_outflow_in_an_act...Sérgio Sacani
Artigo descreve estudo inédito que mostra que os ventos gerados pelos buracos negros nos centros das galáxias pode acabar com o processo de formação de estrelas nas galáxias hospedeiras.
The distribution and_annihilation_of_dark_matter_around_black_holesSérgio Sacani
Uma nova simulação computacional feita pela NASA mostra que as partículas da matéria escura colidindo na extrema gravidade de um buraco negro pode produzir uma luz de raios-gamma forte e potencialmente observável. Detectando essa emissão forneceria aos astrônomos com uma nova ferramenta para entender tanto os buracos negros como a natureza da matéria escura, uma elusiva substância responsável pela maior parte da massa do universo que nem reflete, absorve ou emite luz.
Exocometary gas in_th_hd_181327_debris_ringSérgio Sacani
An increasing number of observations have shown that gaseous debris discs are not an
exception. However, until now we only knew of cases around A stars. Here we present the first
detection of 12CO (2-1) disc emission around an F star, HD 181327, obtained with ALMA
observations at 1.3 mm. The continuum and CO emission are resolved into an axisymmetric
disc with ring-like morphology. Using a Markov chain Monte Carlo method coupled with
radiative transfer calculations we study the dust and CO mass distribution. We find the dust is
distributed in a ring with a radius of 86:0 0:4 AU and a radial width of 23:2 1:0 AU. At
this frequency the ring radius is smaller than in the optical, revealing grain size segregation
expected due to radiation pressure. We also report on the detection of low level continuum
emission beyond the main ring out to 200 AU. We model the CO emission in the non-LTE
regime and we find that the CO is co-located with the dust, with a total CO gas mass ranging
between 1:2 10 6 M and 2:9 10 6 M, depending on the gas kinetic temperature and
collisional partners densities. The CO densities and location suggest a secondary origin, i.e.
released from icy planetesimals in the ring. We derive a CO cometary composition that is
consistent with Solar system comets. Due to the low gas densities it is unlikely that the gas is
shaping the dust distribution.
Forming intracluster gas in a galaxy protocluster at a redshift of 2.16Sérgio Sacani
Galaxy clusters are the most massive gravitationally bound structures in the Universe, comprising thousands of galaxies and
pervaded by a diffuse, hot “intracluster medium” (ICM) that dominates the baryonic content of these systems. The formation
and evolution of the ICM across cosmic time1
is thought to be driven by the continuous accretion of matter from the large-scale
filamentary surroundings and dramatic merger events with other clusters or groups. Until now, however, direct observations of
the intracluster gas have been limited only to mature clusters in the latter three-quarters of the history of the Universe, and we
have been lacking a direct view of the hot, thermalized cluster atmosphere at the epoch when the first massive clusters formed.
Here we report the detection (about 6σ) of the thermal Sunyaev-Zeldovich (SZ) effect2
in the direction of a protocluster. In fact,
the SZ signal reveals the ICM thermal energy in a way that is insensitive to cosmological dimming, making it ideal for tracing
the thermal history of cosmic structures3
. This result indicates the presence of a nascent ICM within the Spiderweb protocluster
at redshift z = 2.156, around 10 billion years ago. The amplitude and morphology of the detected signal show that the SZ
effect from the protocluster is lower than expected from dynamical considerations and comparable with that of lower-redshift
group-scale systems, consistent with expectations for a dynamically active progenitor of a local galaxy cluster.
A giant ring_like_structure_at_078_z_086_displayed_by_gr_bsSérgio Sacani
Uma equipe de astrônomos da Hungria e dos EUA descobriram o que parece ser a maior feição no universo observável: um anel de nove explosões de raios-gamma – e portanto, galáxias – com 5 bilhões de anos-luz de diâmetro. Os cientistas, liderados pelo Prof. Lajos Balazs, do Observatório Konkoloy, em Budapeste, reportou seu trabalho num artigo do Montlhy Notices of the Royal Astronomical Socitey.
Explosões de raios-Gamma as GRBs, são os eventos mais luminosos no universo, lançando o equivalente à energia que o Sol lança em 10 bilhões de anos em poucos segundos. Acredita-se que elas sejam o resultado do colapso de massivas estrelas em buracos negros. A grande luminosidade desses eventos, ajuda os astrônomos a mapearem o local de distantes galáxias, algo que a equipe explorou.
As GRBs que constituem o recém-descoberto anel foram observadas, usando uma grande variedade de telescópios, tanto em Terra como no espaço. Elas aparecem a uma distância muito similar de nós, cerca de 7 bilhões de anos-luz, num círculo de 36 graus através do nosso céu, ou o equivalente a mais de 70 vezes o diâmetro da Lua Cheia. Isso implica que o anel tem mais de 5 bilhões de anos-luz de diâmetro, e de acordo com o Professor Balazs, existe somente a probabilidade de 1 em 20000 das GRBs estarem nessa distribuição por coincidência.
An almost dark galaxy with the mass of the Small Magellanic CloudSérgio Sacani
Almost Dark Galaxies are objects that have eluded detection by traditional surveys such as the Sloan Digital Sky Survey (SDSS). The
low surface brightness of these galaxies (µr(0)> 26 mag/arcsec2
), and hence their low surface stellar mass density (a few solar masses
per pc2 or less), suggests that the energy density released by baryonic feedback mechanisms is inefficient in modifying the distribution
of the dark matter halos they inhabit. For this reason, almost dark galaxies are particularly promising for probing the microphysical
nature of dark matter. In this paper, we present the serendipitous discovery of Nube, an almost dark galaxy with < µV >e∼ 26.7
mag/arcsec2
. The galaxy was identified using deep optical imaging from the IAC Stripe82 Legacy Project. Follow-up observations
with the 100m Green Bank Telescope strongly suggest that the galaxy is at a distance of 107 Mpc. Ultra-deep multi-band observations
with the 10.4m Gran Telescopio Canarias favour an age of ∼ 10 Gyr and a metallicity of [Fe/H]∼ −1.1. With a stellar mass of ∼ 4×108
M⊙ and a half-mass radius of Re = 6.9 kpc (corresponding to an effective surface density of < Σ >e∼ 0.9 M⊙/pc2
), Nube is the most
massive and extended object of its kind discovered so far. The galaxy is ten times fainter and has an effective radius three times larger
than typical ultra-diffuse galaxies with similar stellar masses. Galaxies with comparable effective surface brightness within the Local
Group have very low mass (tens of 105 M⊙) and compact structures (effective radius Re < 1 kpc). Current cosmological simulations
within the cold dark matter scenario, including baryonic feedback, do not reproduce the structural properties of Nube. However, its
highly extended and flattened structure is consistent with a scenario where the dark matter particles are ultra-light axions with a mass
of mB=(0.8
+0.4
−0.2
)×10−23 eV
Presentation in the Science Coffee hosted by the Advanced Concepts Team of the European Space Agency on the 12.01.2024.
Speaker: Benoit Famaey (CNRS - Observatoire astronomique de Strasbourg)
Title: Modified Newtonian Dynamics
Abstract: Presentation around the topic of MOND / tests of MOND
Final parsec problem of black hole mergers and ultralight dark matterSérgio Sacani
When two galaxies merge, they often produce a supermassive black hole binary (SMBHB) at
their center. Numerical simulations with cold dark matter show that SMBHBs typically stall out
at a distance of a few parsecs apart, and take billions of years to coalesce. This is known as the
final parsec problem. We suggest that ultralight dark matter (ULDM) halos around SMBHBs can
generate dark matter waves due to gravitational cooling. These waves can effectively carry away
orbital energy from the black holes, rapidly driving them together. To test this hypothesis, we
performed numerical simulations of black hole binaries inside ULDM halos. Our results imply that
ULDM waves can lead to the rapid orbital decay of black hole binaries.
The first X-ray look at SMSS J114447.77-430859.3: the most luminous quasar in...Sérgio Sacani
SMSS J114447.77-430859.3 (z = 0.83) has been identified in the SkyMapper Southern Survey as the most luminous quasar in
the last ∼ 9 Gyr . In this paper, we report on the eROSITA/Spectrum–Roentgen–Gamma (SRG) observations of the source from
the eROSITA All Sky Survey, along with presenting results from recent monitoring performed using Swift, XMM-Newton, and
NuSTAR. The source shows a clear variability by factors of ∼10 and ∼2.7 overtime-scales of a year and of a few days,respectively.
When fit with an absorbed power law plus high-energy cutoff, the X-ray spectra reveal a = 2.2 ± 0.2 and Ecut = 23+26
−5 keV
. Assuming Comptonization, we estimate a coronal optical depth and electron temperature of τ = 2.5 − 5.3 (5.2 − 8) and
kT = 8 − 18 (7.5 − 14) keV , respectively, for a slab (spherical) geometry. The broadband SED is successfully modelled by
assuming either a standard accretion disc illuminated by a central X-ray source, or a thin disc with a slim disc emissivity profile.
The former model results in a black hole mass estimate of the order of 1010 M , slightly higher than prior optical estimates;
meanwhile, the latter model suggests a lower mass. Both models suggest sub-Eddington accretion when assuming a spinning
black hole, and a compact (∼ 10 rg ) X-ray corona. The measured intrinsic column density and the Eddington ratio strongly
suggest the presence of an outflow driven by radiation pressure. This is also supported by variation of absorption by an order of
magnitude over the period of ∼ 900 d .
The atacama cosmology_telescope_measuring_radio_galaxy_bias_through_cross_cor...Sérgio Sacani
A radiação cósmica de micro-ondas aponta para a matéria escura invisível, marcando o ponto onde jatos de material viajam a velocidades próximas da velocidade da luz, de acordo com uma equipe internacional de astrônomos. O principal autor do estudo, Rupert Allison da Universidade de Oxford apresentou os resultados no dia 6 de Julho de 2015 no National Astronomy Meeting em Venue Cymru, em Llandudno em Wales.
Atualmente, ninguém sabe ao certo do que a matéria escura é feita, mas ela é responsável por cerca de 26% do conteúdo de energia do universo, com galáxias massivas se formando em densas regiões de matéria escura. Embora invisível, a matéria escura se mostra através do efeito gravitacional – uma grande bolha de matéria escura puxa a matéria normal (como elétrons, prótons e nêutrons) através de sua própria gravidade, eventualmente se empacotando conjuntamente para criar as estrelas e galáxias inteiras.
Muitas das maiores dessas são galáxias ativas com buracos negros supermassivos em seus centros. Alguma parte do gás caindo diretamente na direção do buraco negro é ejetada como jatos de partículas e radiação. As observações feitas com rádio telescópios mostram que esses jatos as vezes se espalham por milhões de anos-luz desde a galáxia – mais distante até mesmo do que a extensão da própria galáxia.
Os cientistas esperam que os jatos possam viver em regiões onde existe um excesso de concentração da matéria escura, maior do que o da média. Mas como a matéria escura é invisível, testar essa ideia não é algo tão direto.
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.
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.
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.
Toxic effects of heavy metals : Lead and Arsenicsanjana502982
Heavy metals are naturally occuring metallic chemical elements that have relatively high density, and are toxic at even low concentrations. All toxic metals are termed as heavy metals irrespective of their atomic mass and density, eg. arsenic, lead, mercury, cadmium, thallium, chromium, etc.
The ability to recreate computational results with minimal effort and actionable metrics provides a solid foundation for scientific research and software development. When people can replicate an analysis at the touch of a button using open-source software, open data, and methods to assess and compare proposals, it significantly eases verification of results, engagement with a diverse range of contributors, and progress. However, we have yet to fully achieve this; there are still many sociotechnical frictions.
Inspired by David Donoho's vision, this talk aims to revisit the three crucial pillars of frictionless reproducibility (data sharing, code sharing, and competitive challenges) with the perspective of deep software variability.
Our observation is that multiple layers — hardware, operating systems, third-party libraries, software versions, input data, compile-time options, and parameters — are subject to variability that exacerbates frictions but is also essential for achieving robust, generalizable results and fostering innovation. I will first review the literature, providing evidence of how the complex variability interactions across these layers affect qualitative and quantitative software properties, thereby complicating the reproduction and replication of scientific studies in various fields.
I will then present some software engineering and AI techniques that can support the strategic exploration of variability spaces. These include the use of abstractions and models (e.g., feature models), sampling strategies (e.g., uniform, random), cost-effective measurements (e.g., incremental build of software configurations), and dimensionality reduction methods (e.g., transfer learning, feature selection, software debloating).
I will finally argue that deep variability is both the problem and solution of frictionless reproducibility, calling the software science community to develop new methods and tools to manage variability and foster reproducibility in software systems.
Exposé invité Journées Nationales du GDR GPL 2024
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.
DERIVATION OF MODIFIED BERNOULLI EQUATION WITH VISCOUS EFFECTS AND TERMINAL V...Wasswaderrick3
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The non gravitational_interactions_of_dark_matter_in_colliding_galaxy_clusters
1. The non-gravitational interactions of dark matter in
colliding galaxy clusters
David Harvey1,2∗
, Richard Massey3
, Thomas Kitching4
,
Andy Taylor2
, Eric Tittley2
1
Laboratoire d’astrophysique, EPFL, Observatoire de Sauverny, 1290 Versoix, Switzerland
2
Royal Observatory, University of Edinburgh, Blackford Hill, Edinburgh EH9 3HJ, UK
3
Institute for Computational Cosmology, Durham University, South Road, Durham DH1 3LE, UK
4
Mullard Space Science Laboratory, University College London, Dorking, Surrey RH5 6NT, UK
∗
To whom correspondence should be addressed; E-mail: david.harvey@epfl.ch
Collisions between galaxy clusters provide a test of the non-gravitational forces
acting on dark matter. Dark matter’s lack of deceleration in the ‘bullet cluster
collision’ constrained its self-interaction cross-section σDM/m < 1.25 cm2
/g
(68% confidence limit) for long-ranged forces. Using the Chandra and Hubble
Space Telescopes we have now observed 72 collisions, including both ‘major’
and ‘minor’ mergers. Combining these measurements statistically, we detect
the existence of dark mass at 7.6σ significance. The position of the dark mass
has remained closely aligned within 5.8±8.2 kpc of associated stars: implying a
self-interaction cross-section σDM/m < 0.47 cm2
/g (95% CL) and disfavoring
some proposed extensions to the standard model.
Many independent lines of evidence now suggest that most of the matter in the Universe is
in a form outside the standard model of particle physics. A phenomenological model for cold
dark matter (1) has proved hugely successful on cosmological scales, where its gravitational
influence dominates the formation and growth of cosmic structure. However, there are several
1
2. challenges on smaller scales: the model incorrectly predicts individual galaxy clusters to have
more centrally concentrated density profiles (2), larger amounts of substructure (3, 4), and the
Milky Way to have more satellites able to produce stars (5) than are observed. These incon-
sistencies could be resolved through astrophysical processes (6), or if dark matter particles are
either warm (7) or self-interact with cross-section 0.1 ≤ σDM/m ≤ 1 cm2
/g (8–10). Follow-
ing (11), we define the momentum transfer per unit mass σDM/m, integrating over all scattering
angles and assuming that individual dark matter particles are indistinguishable.
Self-interaction within a hidden dark sector is a generic consequence of some extensions
to the standard model. For example, models of mirror dark matter (12) and hidden sector dark
matter (12–16) all predict anisotropic scattering with σDM/m ≈ 1 barn/GeV = 0.6 cm2
/g,
similar to nuclear cross-sections in the standard model. Note that couplings within the dark
sector can be many orders of magnitude larger than those between dark matter and standard
model particles, which is at most of order picobarns (17).
In terrestrial collider experiments, the forces acting on particles can be inferred from the
trajectory and quantity of emerging material. Collisions between galaxy clusters, which contain
dark matter, provide similar tests for dark sector forces. If dark matter’s particle interactions
are frequent but exchange little momentum (via a light mediator particle that produces a long-
ranged force and anisotropic scattering), the dark matter will be decelerated by an additional
drag force. If the interactions are rare but exchange a lot of momentum (via a massive mediator
that produces a short-ranged force and isotropic scattering), dark matter will tend to be scattered
away and lost (11,18,19).
The dynamics of colliding dark matter can be calibrated against that of accompanying stan-
dard model particles. The stars that reside within galaxies, which are visible in a smoothed map
of their optical emission, have effectively zero cross-section because they are separated by such
vast distances that they very rarely collide. The diffuse gas between galaxies, which is visible
2
3. in X-ray emission, has a large electroweak cross-section; it is decelerated and most is eventu-
ally stripped away by ram pressure (20). Dark matter, which can be located via gravitational
lensing (21), behaves somewhere on this continuum (Fig. 1).
The tightest observational constraints on dark matter’s interaction cross-section come from
its behavior in the giant ‘bullet cluster’ collision 1E0657-558 (22). A test for drag yields
σDM/m < 1.25 cm2
/g (68% CL), and a test for mass loss yields σDM/m < 0.7 cm2
/g (68%
CL) (18). Half a dozen more galaxy cluster collisions have since been discovered, but no tighter
constraints have been drawn. This is because the analysis of any individual system is fundamen-
tally limited by uncertainty in the 3D collision geometry (the angle of the motion with respect
to our line of sight, the impact parameter, and the impact velocity) or the original mass of the
clusters.
The same dynamical effects are also predicted by simulations in collisions between low-
mass systems (11). Observations of low-mass systems produce noisier estimates of their mass
and position (23–25), but galaxy clusters continually grow through ubiquitous ‘minor mergers’,
and statistical uncertainty can be decreased by building a potentially very large sample (26,27).
Furthermore, we have developed a statistical model to measure dark matter drag from many
noisy observations, within which the relative trajectories of galaxies, gas, and dark matter can
be combined in a way that eliminates dependence upon 3D orientation and the time since the
collision (28).
We have studied all galaxy clusters for which optical imaging exists in the Hubble Space
Telescope (Advanced Camera for Surveys) data archive (29) and X-ray imaging exists in the
Chandra Observatory data archive (30). We select only those clusters containing more than
one component of spatially extended X-ray emission. Our search yields 30 systems, mostly
between redshift 0.2 < z < 0.6 plus two at z > 0.8, containing 72 pieces of substructure in
total (Table S1). In every piece of substructure, we measure the distance from the galaxies to
3
4. the gas δSG. Assuming this lag defines the direction of motion, we then measure the parallel δSI
and perpendicular δDI distance from the galaxies to the lensing mass (Fig. 2).
We first test the null hypothesis that there is no dark matter in our sample of clusters (a
similar experiment was first carried out on the Bullet Cluster, finding a 3.4 and 8σ detection
(31)). Observations that do not presuppose the existence of dark matter (32) show that 1014
M
clusters contain only 3.2% of their mass in the form of stars. We compensate for this mass,
which pulls the lensing signal towards the stars and raised δGI by an amount typically 0.78 ±
0.30 kpc (computed using the known distances to the stars δSG; see Materials and Methods).
The null hypothesis is that the remaining mass must be in the gas. However, we observe a
spatial offset between that is far from the expected overlap, even in the presence of combined
noise from our gravitational lensing and X-ray observations (Fig. 3A). A Kolmogorov-Smirnov
test indicates that the observed offsets between gas and mass are inconsistent with the null
hypothesis at 7.6σ, a p-value of 3 × 10−14
(without compensation for the mass of stars, this
is 7.7σ). This test thus provides direct evidence for a dominant component of matter in the
clusters that is not accounted for by the luminous components.
Having reaffirmed the existence of dark matter, we attempt to measure any additional drag
force acting upon it, caused by long-range self-interactions. We measure the spatial offset of
dark matter behind the stars, compensating as before for the 16% of mass in the gas (33) by
subtracting a small amount from δSI (on average 4.3 ± 1.6 kpc). We measure a mean dark
matter lag of δSI = −5.8 ± 8.2 kpc in the direction of motion (Fig. 3B), and δDI = 1.8 ±
7.0 kpc perpendicularly. The latter is useful as a control test: symmetry demands that it must
be consistent with zero in the absence of systematics. We also use its scatter as one estimate of
observational error in the other offsets.
We interpret the lag through a model (28) of dark matter’s optical depth (similarly to pre-
vious studies (19, 23)). Gravitational forces act to keep gas, dark matter and galaxies aligned,
4
5. while any extra drag force on dark matter induce a fractional lag
β ≡
δSI
δSG
= B 1 − e
−(σDM−σgal)
σ /m
, (1)
where σgal is the interaction cross-section of the galaxies, coefficient B encodes the relative
behavior of dark matter and gas, and σ /m is the characteristic cross-section at which a halo of
given geometry becomes optically thick. We assume that stars do not interact, so σgal ≈ 0. To
ensure conservative limits on σDM/m, we also assume B ≈ 1 and marginalize over σ /m ≈
6.5 ± 3 cm2
/g, propagating this broad uncertainty to our final constraints (see Materials and
Methods). Adopting the dimensionless ratio β brings two advantages. First, it removes de-
pendence on the angle of the collision with respect to the line of sight. Second, it represents
a physical quantity that is expected to be the same for every merger configuration, so mea-
surements from the different systems can be simply averaged (with appropriate noise weight-
ing, although in practice, the constraining power from weak lensing-only measurements comes
roughly equally from all the systems).
Combining measurements of all the colliding systems, we measure a fractional lag of dark
matter relative to gas β = −0.04±0.07 (68% CL). Interpreting this through our model implies
that dark matter’s momentum transfer cross-section is σDM/m = −0.25+0.42
−0.43 cm2
/g (68% CL,
two-tailed), or σDM/m < 0.47 cm2
/g (95%CL, one-tailed); the full PDF is shown in Fig. 4.
This result rules out parts of model space of hidden sector dark matter models e.g. (12,13,15,16)
that predict σDM/m ≈ 0.6 cm2
/g on cluster scales through a long-range force. The control test
found β⊥ ≡ δDI/δSG = −0.06 ± 0.07 (68% CL), consistent with zero as expected. This
inherently statistical technique can be readily expanded to incorporate much larger samples
from future all-sky surveys. Equivalent measurements of mass loss during collisions could also
test dark sector models with isotropic scattering. Combining observations, these astrophysically
large particle colliders have potential to measure dark matter’s full differential scattering cross-
5
7. found via gravitational lensing
Dark matter
visible in X-rays
Hot, diffuse gas
(Stars in) galaxies
visible in optical
Direction of motion
I
S
G D
Figure 1: Cartoon showing the three components in each piece of substructure, and their relative
offsets, illustrated by black lines. The three components remain within a common gravitational
potential, but their centroids become offset due to the different forces acting on them, plus
measurement noise. We assume the direction of motion to be defined by the vector from the
diffuse, mainly hydrogen gas (which is stripped by ram pressure) to the galaxies (for which
interaction is a rare event). We then measure the lag from the galaxies to the gas δSG, and to the
dark matter in a parallel δSI and perpendicular δDI direction.
7
8. 100 kpc 100 kpc 100 kpc 100 kpc 100 kpc
100 kpc 100 kpc 100 kpc 100 kpc 100 kpc
100 kpc 100 kpc 100 kpc 100 kpc 100 kpc
100 kpc 100 kpc 100 kpc 100 kpc 100 kpc
100 kpc 100 kpc 100 kpc 100 kpc 100 kpc
100 kpc 100 kpc 100 kpc 100 kpc 100 kpc
20" 20" 20" 20" 20"
20" 20" 20" 20" 20"
20" 20" 20" 20" 20"
20" 20" 20" 20" 20"
20" 20" 20" 20" 20"
20" 20" 20" 20" 20"
1E0657 A1758 A209 A2146 A2163
A2744 A370 A520 A781 ACTCLJ0102
DLSCLJ0916 MACSJ0025 MACSJ0152 MACSJ0358 MACSJ0416
MACSJ0417 MACSJ0553 MACSJ0717 MACSJ1006 MACSJ1226
MACSJ1354 MACSJ1731 MACSJ2243 MS1054 RXCJ0105
RXCJ0638 RXJ1000 SPTCL2332 ZWCL1234 ZWCL1358
Figure 2: Observed configurations of the three components in the 30 systems studied. The
background shows the HST image, with contours showing the distribution of galaxies (green),
gas (red) and total mass, which is dominated by dark matter (blue).
8
9. Observed offset between various components of substructure [kpc]
-200 -100 0 100 200 300 400
20B
15A
δ
(galaxies-gas)
δ
(galaxies-dark matter)
δ
(gas-dark matter)
GI
SI
GI
Figure 3: Observed offsets between the three components of 72 pieces of substructure. Offsets
δSI and δGI include corrections accounting for the fact that gravitational lensing measures the
total mass, not just that of dark matter. (A) The observed offset between gas and mass, in the
direction of motion. The smooth curve shows the distribution expected if dark matter does not
exist; this hypothesis is inconsistent with the data at 7.6σ statistical significance. (B) Observed
offsets from galaxies to other components. The fractional offset of dark matter towards the gas,
δSI/δSG, is used to measure the drag force acting on the dark matter.
9
10. Posteriorprobability(linearscale)
Dark matter self-interaction cross section, [cm /g]2σDM
-2 -1 0 1 2 3 4
(Bulletcluster)
bulletcluster
(Babybullet)
(Pandora’scluster)
1E0657-558
Masslossin
MACSJ0025
Abell2744
Figure 4: Constraints on the self-interaction cross-section of dark matter. These are derived
from the separations β = δSI/δSG, assuming a dynamical model to compare the forces acting
on dark matter and standard model particles (28). The hatched region denotes 68% confidence
limits, to be compared to the 68% confidence upper limits from previous studies of the most
constraining individual clusters in blue. Note that the tightest previous constraint is derived
from a measurement of dark matter mass loss, which is sensitive to short range self-interaction
forces; all other constraints are measurements of a drag force acting on dark matter, caused by
long range self-interactions.
10
11. Acknowledgements
DH is supported by the Swiss National Science Foundation (SNSF) and STFC. RM and TK
are supported by the Royal Society. The raw HST and Chandra data are all publicly accessible
from the mission archives (29, 30). We thank the anonymous referees, plus Scott Kay, Erwin
Lau, Daisuke Nagai and Simon Pike for sharing mock data on which we developed our analy-
sis methods; Rebecca Bowler for help stacking HST exposures; Eric Jullo, Jason Rhodes and
Phil Marshall for help with shear measurement and mass reconstruction; Doug Clowe, Hakon
Dahle and James Jee for discussions of individual systems; Celine Boehm, Felix Kahlhoefer
and Andrew Robertson for interpreting particle physics.
11
12. Supplementary materials for
The non-gravitational interactions of dark matter in colliding
galaxy clusters
David Harvey1,2
, Richard Massey3
, Thomas Kitching4
, Andy Taylor2
& Eric Tittley2
1Laboratoire d’astrophysique, EPFL, Observatoire de Sauverny, 1290 Versoix, Switzerland
2Royal Observatory, University of Edinburgh, Blackford Hill, Edinburgh EH9 3HJ, UK
3Institute for Computational Cosmology, Durham University, South Road, Durham DH1 3LE, UK
4Mullard Space Science Laboratory, University College London, Dorking, Surrey RH5 6NT, UK
Correspondence to: david.harvey@epfl.ch
This PDF file includes:
• Materials and Methods
• SupplementaryText
• Figs. S1 to S8
• References 32–47
1
13. Materials and methods
We followed overall procedures that we developed in blind tests on mock data (24), usually exploiting
algorithms for high precision measurement that had been developed, calibrated and verified elsewhere.
However, several custom adaptations were required to analyze the heterogeneous data from the Hubble
Space Telescope (HST) and Chandra X-ray Observatory archives (Table S1 lists all the observed systems,
and Figure S2 shows the offsets measured in each).
Here we describe the methods we used to combine observations with different exposure times, fil-
ters, epochs and orientations – starting from the raw data and performing a full reduction to maximise
data quality. To convert angular distances into physical distances, we assume a cosmological model
derived from measurements of the Cosmic Microwave Background (33), ΩM = 0.31, ΩΛ = 0.69,
H0 = 67 km/s/Mpc.
Position of gas, seen in X-ray emission
We downloaded the raw event 1 files for all observations. To process these data, we used CIAO tools
version 4.5, starting with basic reduction and calibration using the CIAO repro tool. In our analysis, it is
particularly important to remove emission from point sources, and prevent X-ray bright Active Galactic
Nuclei at the centers of clusters from biasing our position measurements. We therefore made a first pass
at removing point sources using celldetect. We then filtered each event table for any potential spurious
events such as solar flares by clipping the table at the 4σ below the mean flux level.
Having cleaned each exposure, we combined them using the merge obs script from CIAO tools into
a single exposure map corrected flux image, producing along with it exposure maps for each observation
and the stacked image. We modeled the Chandra PSF at each position throughout the field, we created
individual maps using mkpsfmap for each exposure at an effective energy of 1 keV, then combined each
model weighting them by their respective exposure map. Figure S3 shows an example of the PSF map
used for cluster A520.
To make a second pass to identify point sources, we passed the stacked image and PSF model through
CIAO wavdetect, a wavelet smoothing algorithm that employs a ‘Mexican hat’ filter on a range of scales.
This estimates the true size of each source, correcting for the size of the PSF. We used the smallest
scales for the wavelet radii (1, 2 pixels) to identify point sources, and combined the larger scales (4,
8, 16, and 32 pixels) into a denoised version of the final image. We finally inspected every image by
eye for any remaining point sources. We found that this double filter method proved very successful at
removing point sources, with only AGN at the edge of the cluster remaining unflagged. Although their
emission has extended wings, the cluster is usually in the center of the pointing, resulting in minimal
contamination.
Finally, we measured the position of coherent substructure in the X-ray emission using SExtrac-
tor (34). This calculates positions from the first order moments of the light profile, which means that the
returned position does not always coincide exactly with the brightest pixel. SExtractor does not report
reliable errors in the positions but, since the dominant contribution of variation is the size of the smooth-
ing kernel, we can estimate the robustness of our measurements by smoothing the image using different
scales in wavdetect, and measure the rms across different scales. On average we found the rms error to
be 4 arcseconds (roughly 30 kpc at redshift z=0.4).
2
14. Cluster RA (deg) DEC (deg) z ACS Filter ACS (s) Chandra (ks)
1E0657 104.612 -55.9477 0.296 F814W F775W 15094.0 597.39
A1758 203.194 50.5426 0.2792 F814W 10000.0 216.00
A209 22.9728 -13.6127 0.206 F814W 4040.00 24.09
A2146 239.007 66.3725 0.234 F814W 9233.00 84.08
A2163 243.938 -6.14690 0.203 F814W 9192.00 444.59
A2744 3.58210 -30.3898 0.308 F814W 11980.0 133.12
A370 39.9627 -1.58000 0.373 F814W 3840.00 86.81
A520 73.5395 2.93110 0.202 F814W 18320.0 426.01
A781 140.149 30.4927 0.298 F814W 1620.00 49.54
ACTCLJ0102 15.7277 -49.2560 0.87 F814W 1916.00 359.16
DLSCLJ0916 139.046 29.8450 0.5343 F814W 9894.00 41.28
MACSJ0025 6.37460 -12.3818 0.5843 F814W 4200.00 168.61
MACSJ0152 28.1473 -28.8944 0.341 F606W 1200.00 20.04
MACSJ0358 59.7174 -29.9320 0.428 F814W 4620.00 65.74
MACSJ0416 64.0392 -24.0735 0.42 F814W 4037.00 57.50
MACSJ0417 64.3926 -11.9111 0.443 F814W 1910.00 95.92
MACSJ0553 88.3494 -33.7117 0.407 F814W 4572.00 88.74
MACSJ0717 109.389 37.7528 0.5458 F814W 8893.00 83.22
MACSJ1006 151.730 32.0198 0.359 F814W 1440.00 13.30
MACSJ1226 186.694 21.8673 0.37 F814W 5520.00 153.81
MACSJ1354 208.635 77.2528 0.3967 F814W 1200.00 35.46
MACSJ1731 262.913 22.8660 0.389 F814W 1440.00 22.28
MACSJ2243 340.837 -9.58910 0.447 F606W 1200.00 21.88
MS1054 164.245 -3.62000 0.826 F606W 8100.00 89.51
RXCJ0105 16.4096 -24.6801 0.23 F606W 1200.00 21.97
RXCJ0638 99.6953 -53.9735 0.1658 F606W 1200.00 21.78
RXJ1000 150.132 44.1491 0.154 F606W 1200.00 20.66
SPTCL2332 352.959 -50.8642 0.5707 F606W 7680.00 39.9
ZWCL1234 189.045 28.9929 0.2214 F814W 27632.0 51.75
ZWCL1358 209.951 62.5163 0.329 F850LP 13692.0 63.10
1
Figure S1: The full sample of 30 merging complexes, and their locations on the sky. The
columns show, from left to right: the name of the cluster, its right ascension, declination, and
redshift, the HST/ACS filter used for our lensing analysis, and the total exposure time for that
particular filter, and the (cleaned) exposure time of the Chandra X-ray image.
3
15. −300 −200 −100 0 100 200 300
Offset [kpc]
ZWCL1358
ZWCL1234
SPTCL2332
RXJ1000
RXCJ0638
RXCJ0105
MS1054
MACSJ2243
MACSJ1731
MACSJ1354
MACSJ1226
MACSJ1006
MACSJ0717
MACSJ0553
MACSJ0417
MACSJ0416
MACSJ0358
MACSJ0152
MACSJ0025
DLSCLJ0916
ACTCLJ0102
A781
A520
A370
A2744
A2163
A2146
A209
A1758
1E0657
Figure S2: Observed offsets between galaxies, gas and dark matter in 72 components of sub-
structure. In each case, the green triangle, at the centre of the coordinate system, denotes the
position of the galaxies. The separation between galaxies and gas, δSG, is shown in red. The
separation of the dark matter with respect to the galaxies, projected onto the SG vector, δSI, is
shown in blue. The error bars show the locally estimated 1σ errors.
4
16. Size (arcseconds)
100
101
73.5650 73.5633 73.5616 73.5599 73.5583
RA (degrees)
2.8547
2.8564
2.8581
2.8597
2.8614
DEC(degrees)
Figure S3: An example model of the size of the Chandra X-ray telescope’s Point Spread Func-
tion (PSF). The model PSF is used to identify and remove point sources, e.g. Active Galactic
Nuclei – and to thereby identify extended X-ray emission from hot gas within the cluster. The
image shows a combined, exposure map weighted, PSF map stacked for the various observa-
tions of galaxy cluster A520.
5
17. Position of galaxies, seen in optical emission
We searched the HST archive for data acquired with the Advanced Camera for Surveys (ACS) instrument,
which has the largest field of view. We considered only filters F606W, F814W and F850LP, whose high
throughput ensures deep imagining, and whose red wavelengths ensure (a) that the optical emission
samples the old stars that dominate the mass content of these systems and (b) a high density of high
redshift galaxies visible behind the cluster, to provide sufficient lensing signal. Some clusters had been
observed in more than one wavelength band. We used only a single band for all the clusters to further
homogenize the data, but have compared a subset of our results in different bands to check for systematic
errors. For our main analysis, we selected the broad F814W band, unless there are significantly more
exposures in another.
We corrected the raw, pixellated data for charge transfer inefficiency (35), then performed basic data
reduction and calibration using the standard Calacs pipeline. We used tweakReg to orient and align
individual exposures, then stacked them using MultiDrizzle (36) with a Gaussian convolution kernel and
PIXFRAC=0.8 (37) to produce a deep, mosaicked image with a pixel scale of 0.03 arcseconds. In the
process, MultiDrizzle also output a reoriented image of each individual exposure, which we used for
star/galaxy identification and PSF estimation.
We estimated the distribution of mass in galaxies via the proxy of the light emitted by their stars. In
our single-band imaging, we were able to identify and mask foreground stars in the Milky Way (which
appear pointlike), but assumed any foreground or background galaxies to be randomly positioned and
thus merely add shot noise to our measurements. We smoothed the masked image using wavdetect, and
measured the position of coherent substructure using SExtractor (34). This calculates positions from the
first order moments of the light profile, which means that the returned position does not always coincide
exactly with the brightest pixel. SExtractor does not report reliable errors in the positions. However,
since the dominant contribution of noise is inclusion or omission of galaxies inside the smoothing ker-
nel, we estimated the robustness of our measurements by smoothing the image using different scales in
wavdetect, and compared the resulting positions. On average, we found an rms error in the position of
the extracted halos of 0.6 arcseconds (roughly 4.5 kpc at redshift z=0.4).
We also tried two other ways to quantify the position of the galaxies. First, we measured the
smoothed distribution of galaxies in the image, with all galaxies weighted equally (this represents the
opposite – and least realistic – assumption of galaxies’ mass/light ratio). To do this in practice, we
passed the galaxy catalogue through the X-ray data reduction pipeline, as if each galaxy were a single
X-ray photon. This created a smoothed image, in which we identified substructure using SExtractor.
Since the same galaxies contributed both to the flux-weighted and galaxy-weighted positions, the two
measurements are correlated. We measure the uncertainty on the galaxy weighted positions to be 5 kpc,
about the same as the flux-weighted positions. We obtain consistent values of β = 0.054±0.062 (68%
CL) and conclude that σDM/m = 0.36+0.46
−0.45 cm2/g (68% CL, two-tailed). Second, we tried identifying
the position of the ‘Brightest Group Galaxy’ (BGG), since its formal error is small, and it has proved
optimal in studies of isolated groups (38). In merging systems however, the brightest nearby galaxy is
frequently unassociated with the infalling group (39). Accounting for our observed 1.7 ± 0.9 arcsecond
offset to any brighter galaxy within 25 arcseconds of X-ray emission (the search region that will be used
to identify gravitational lensing signals), again yields a consistent constraint on σDM/m, but with much
larger final error.
6
18. Position of dark matter, measured via weak gravitational lensing
We measured the ellipticities of galaxies in HST images using the RRG method (40). This corrects
galaxies’ Gaussian-weighted moments for convolution with the Point Spread Function (PSF), to measure
the shear γ1 (γ2) corresponding to elongations along (at 45 degrees to) the x axis. This method has been
empirically calibrated on simulated HST imaging in which the true shear is known (41), applying a
multiplicative correction of m = −3.0 × 10−3 and a additive bias of c = −2.1 × 10−4.
HST’s PSF varies across the field of view and, because thermal variations change the telescope’s
focus, at different epochs. Modelling the net PSF in our stacked images therefore required a flexible
procedure. We first identified stars in the deep, stacked image using their locus in size–magnitude space.
We then measured the ellipticity of each star in individual exposures. By comparing these to TinyTim (42)
models of the HST PSF (created by raytracing through the telescope at different focus positions but at
the appropriate wavelengths for the band), we determined the focus position for each exposure. We then
interpolated (second and fourth shape moments of) the TinyTim PSF model to the position of the galaxies,
rotating into the reference frame of the MultiDrizzle mosaic. We then summed the PSF moments from
each exposure in which a galaxy was observed. Figure S4 shows an example of the final PSF model for
one cluster.
We measured the shear of all galaxies that appear in 3 or more exposures, with a combined signal-to-
noise in the stacked image > 4.4 and size > 0.1 arcseconds. These cuts (41) remove noisy measurements
at the edges of the field or in the gaps between detectors. We also masked out galaxies that lie near bright
stars or large galaxies, whose shapes appear biased. Figure S5 compares shear catalogues for a single
cluster, derived from independent analyses of data in the F814W and F606W bands. There is the expected
level of scatter between the two measurements – but, most importantly, there is no detectable bias.
We reconstructed the distribution of mass in the clusters using the parametric model-fitting algo-
rithm Lenstool (43). Using Bayesian likelihood minimization, Lenstool simultaneously fits multiple mass
haloes to an observed shear field, with the position and shape of each halo described by the NFW (44)
density profile. This is an efficient technique to record a unique position for each halo, marginalizing
over nuisance parameters that include mass and morphology, that are not of direct interest to our study.
Assuming this density profile does not bias measurements of the position of halos within current statis-
tical limits (24). Lenstool requires positional priors to be defined in which it searches for the lensing
signal. Except in a few well-studied systems (where we use the extra information), we obtained an initial
lensing model using one prior search radius centered on each gas position and large enough to incorpo-
rate any nearby groups of galaxies. Following this scheme, we used an automated procedure to identify
and associate the mutually closest galaxy, gas and lensing signals into systems of three mass components.
In all systems, we then modeled the lensing system a final time, adopting priors centred on the galaxy
position (we redid this step when trying different position estimators for the galaxies). Henceforth, we
could center the coordinate system for each combined system of galaxies, gas and dark matter on the
galaxies, to avoid prior bias in the Bayesian fits.
Lenstool samples the posterior surface in two ways. To obtain the best fitting position, we iterated
to the best-fit solution with a converging MCMC step size, using ten simultaneous sampling chains to
avoid local maxima. To sample the entire posterior surface (whose width quantifies uncertainty on model
parameters), we then reran the algorithm with a fixed step size. The 1σ error on position was on average
11.4 arcseconds (roughly 60 kpc at redshift z=0.4). As a sanity check we compare our measured centroids
to those systems included in previous studies. Our statistical uncertainty is sometimes larger because we
7
19. 0 2000 4000 6000 8000 10000
X [PIXELS]
0
2000
4000
6000
8000
10000
Y[PIXELS]
Ellipticity = 0.01
Figure S4: An example model of the Point Spread Function (PSF) of the Hubble Space Tele-
scope/Advanced Camera for Surveys (HST/ACS). Each tick mark represents the ellipticity of
the PSF at that particular position in the HST field. Its orientation shows the PSF’s major axis
and its length shows the ellipticity; a dot would indicate a circular PSF. The PSF tends to be
highly elliptical near the edge of the field and more circular in the centre. Tick marks are plot-
ted at the position of every “detected” source. The mosaic pattern of dithered exposures can be
seen: noisier regions with fewer exposures contain more spurious sources, which are removed
during analysis (but are shown here for clarity). The example shown is for observations of
galaxy cluster MACSJ0416.
8
20. 18 20 22 24 26
Magnitude
−1.0
−0.5
0.0
0.5
1.0
γ1
F814W
−γ1
F606W
18 20 22 24 26
Magnitude
−1.0
−0.5
0.0
0.5
1.0
γ2
F814W
−γ2
F606W
Figure S5: A comparison of the gravitational lensing shears measured independently behind a
single cluster, in two different HST filters. The top (bottom) panel shows the difference between
γ1 (γ2) for each galaxy, which traces to elongations along (at 45 degrees to) the x axis. We find
scatter as expected due to observational noise, but no systematic bias.
9
21. use only weak gravitational lensing, but we find no evidence for any bias. For example, our measured
positions in the ‘bullet cluster’ lie within one standard deviation of those reported in (31).
Positional offsets between components
When assigning different mass components to one another, for almost all the clusters, we used an auto-
mated matching algorithm to associate the nearest clumps of dark matter, gas and stars. This was made
robust by performing the matching in both directions (e.g., dark matter to stars, and stars to dark matter).
In a few cases where detailed analyses of individual systems were available in the literature (for exam-
ple, using strong lensing, X-ray shocks, optical spectroscopy or imaging additional bands, which were
outside the scope of our work), we inserted that prior information by hand during association. This was
most useful in systems A520 and A2744. As a further test, we carry out a jackknife test to ensure that the
association does not effect the overall constraints, and moreover, no single cluster dominates the result.
We find no evidence for such an effect, and derive consistent error bars of ∆σDM,JK/m = ±0.5cm2/g,
further supporting the error bars quoted in our final result.
We drew an offset vector δSG in angle between the observed position of the gas and galaxies, which
we took to define the system’s direction of motion. We then measured the position of the total mass along
that vector and (in a right handed coordinate system) perpendicular to it, defining offset vectors δSI, δGI,
and δDI from the intersection point I of these vectors.
Gravitational lensing measures the position of total mass, rather than that of just dark matter. We
corrected the measured offsets δSI and δGI for the contribution from the next most massive component.
To calibrate this correction, we analysed mock lensing data from a dominant mass component (with
an NFW (44) profile) plus a less massive component at some offset δ. The corrections were always
small but, for a subdominant component with the same profile, normalised to contain a fraction f of the
total mass, we found that the lensing position is pulled by an amount fδe−0.01δ/rs , and we corrected
for that. If we do not calibrate for the extra pull of gas on the lensing peak we infer an upper limit of
σDM/m < 0.54cm2/g (68% CL, one-tailed).
To test the hypothesis that dark matter does not exist, we required a model of the δGI data expected
if this were true. To generate that model, we assumed that the true positions of the X-ray and lensing
signals coincided, but that the observed positions were offset by a random amount determined by the
appropriate level of noise in each (see above). We calculated the 2D offset, then projected this onto the
direction to the stars, which is also selected at random. We could have slightly increased the model δGI
offset to account for the mass in stars (the increase must be positive because the vector δSG is defined
from the galaxies to the gas). However, it is better to instead decrease the observed δGI offset. The two
approaches are equivalent in principle, but the latter allowed information to be added to our analysis
because the absolute value of δSG was known in each system. When comparing the model and observed
δGI offsets via a Kolmogorov-Smirnov test (in which we computed critical values using a Taylor series),
we also used the errors on σGI determined for each system individually.
When measuring the interaction cross-section of dark matter, we converted offset measurements in
arcseconds to physical units of kpc (using a standard cosmological model, which assumes dark matter
exists). This enabled a more detailed comparison of the offsets between different systems. The (nois-
ily determined) error estimates of offsets in a few systems were anomalously low, and likely smaller
than the uncertainty in our knowledge of the merging configuration. To more robustly quantify the to-
tal uncertainty of offsets (which should include observational noise plus the possibility of component
10
22. misidentification and merging irregularities), we empirically exploited the control test δDI, which has
an rms variation between systems σDI = 60 kpc. This value is consistent with most of the individually
measured errors, but more robust. We therefore adopted it globally as the error on every measurement
of δDI and δSI, rescaling to a value in arcseconds at the redshift of each system. Errors in δSG must be
smaller than this, because they do not involve observational noise in the lensing position. However, they
also include the possibility of component misidentification, which is best estimated through this global
approach. We therefore adopted the conservative approach of also assigning this value as the error on
every measurement of δSG. Thus we set σSG = σSI = σDI = 60 kpc. To combine our measurements of
β = δSI/δSG and β⊥ = δDI/δSG from individual systems, we multiplied their posterior probabilities (ap-
proximated as a normal distribution even though it is a Cauchy distribution, but with a width determined
by propagating errors on the individual offsets).
Interpreting positional offsets as an interaction cross-section
Similarly to previous studies of the cross-section of dark matter (19,23), we interpreted observations of
offset dark matter in terms of its optical depth for interactions. However, we have developed a more
sophisticated model (28) intended to take into account the 3D and time-varying trajectories of infalling
halos. First, calculating the dimensionless ratio β = δSI/δSG removes dependence on the angle of the
collision with respect to the line of sight. Furthermore, a set of analytic assumptions suggests that β
is a physically meaningful quantity that should be the same for every system. The main assumption of
quasi-steady state equilibrium is reasonable for the detectable systems in our sample, but caution would
be needed to interpret dark matter substructure that had passed directly through the cluster core (and
had its gas stripped) or substructure on a radial orbit caught at the brief moment of turnaround (this is
a negligible fraction in our mock data). The model also incorporates the results of simulations (11) in
which dark sector interactions that are frequent but exchange little momentum (e.g. via a light mediator
particle that produces a long-ranged force and anisotropic scattering) produce a drag force and separate
dark matter from the stars. On the other hand, simulations of ‘billiard ball’ interactions that are rare
but exchange a lot of momentum (e.g. via a massive mediator that produces a short-ranged force and
isotropic scattering) tend to scatter dark matter away from a system and produce mass loss (11, 18, 19).
However, we note that the ref. (18) also reports an unexpected small separation between galaxies and
dark matter after billiard ball scattering. In this paper, we explicitly follow the prescription in (11).
According to our model of dark matter dynamics (see equation 33 of ref. (28)), the offset of dark
matter from galaxies, calibrated against the offset of gas, is
β = B 1 − exp
−(σDM − σgal)
σ
. (S1)
Since the gaps between galaxies are vast compared to their size, they interact very rarely, so we assumed
that σgal ≈ 0. If this assumption were wrong, or in the presence of observational noise, our analysis
can therefore produce negative values of σDM/m. Our quoted errors include observational errors, pair-
assignment errors, and model parameter errors.
The value of σ /m depends upon the geometrical properties of the dark matter halo, but is pro-
portional to its mass and inversely proportional to its cross-sectional area. For our set of merging
systems, we conservatively adopted a σ /m = 6.5 ± 3 cm2/g by assuming the system masses are
11
23. log(M200/M ) = 14 ± 1, with NFW density profiles and concentration varying with mass as ob-
served in numerical simulations (45). By assuming a conservative range in halo masses we propagate
a much larger error in σ /m than one would expect if we were to measure the true values. We then
analytically marginalized over σ /m, propagating the uncertainty through to our final constraints. The
top panel of Figure S6 shows the values of σ /m instead assuming different, fixed system masses; the
bottom panel shows the effect on σDM/m. The inferred estimate of σDM/m is broadly insensitive to
σ /m, varying from σDM/m = −0.23 ± 0.60 cm2/g for an assumed halo of M200 = 1013M to
σDM/m = −0.1 ± 0.28 cm2/g for a halo of M200 = 1015M .
The relative behaviour of gas and dark matter was compared through a ratio in the prefactor
B =
CDMADMMgasρDM
CgasAgasMDMρgas
, (S2)
where C, A and M are the drag coefficient, size and mass of the merging halo, and ρ is the density
of material through which it is moving. We assumed a conservative lower limit of B >
∼ 1, leading to a
conservative upper limit on our constraints on σDM/m.
The first requirement to have ensured a conservative treatment is that the infalling substructure’s gas
envelope is smaller than its dark matter envelope, Agas < ADM. This is generically true of isolated
structures in numerical simulations and, as gas is stripped during the collision, it will become smaller
still. The geometric size of a gas halo also depends upon its temperature – and hot gas may be more easily
stripped than cold gas. To test whether that has an statistically significant effect, we measured the X-ray
temperature of each observed infalling system, and separately analyzed the hotter and cooler halves of
our sample. As shown in Figure S7, the results for each half remain consistent, with error bars larger
by approximately
√
2. For the hotter sample (T > 8 keV), we found σDM/m = −0.10 ± 0.58 cm2/g
and for the cooler sample (T < 8 keV) we found σDM/m = −0.50 ± 0.64 cm2/g. Although there was
marginal evidence that hot gas is more easily stripped than cold gas, which could be investigated with a
much larger sample, our conclusions remain unaffected within current statistical precision.
The second requirement to have ensured a conservative treatment is that the gas fraction in the
medium through which the bullet is traveling, fgas ≡ ρgas/ρDM is less than that of the infalling struc-
ture Mgas/MDM. We assumed that, overall, infalling structure contains the universal fraction ΩB/ΩD =
0.184 (33), and we measured fgas in mock data realised from cosmological simulations of structure
formation (46). The mean fgas over all simulations (the solid line in Figure S8) is lower than the uni-
versal fraction, and is indeed constant (within 10%) at the radii of observable substructures (points in
Figure S8). These conclusions from simulations are consistent with deep X-ray observations of galaxy
clusters, e.g. (47).
12
24. −2 −1 0 1 2 3 4
σDM/m [ cm2
/g ]
0.000
0.005
0.010
0.015
p(σDM/m)
σ*/m=9.5cm2
/g
σ*/m=7.9cm2
/g
σ*/m=6.5cm2
/g
σ*/m=5.4cm2
/g
σ*/m=4.4cm2
/g
1013
1014
1015
MH [ MSUN ]
4
5
6
7
8
9
10
σ*/m[cm2
/g]
82 104 133 169 214 272 346 440 559
Size [ kpc ]
Figure S6: The sensitivity of measurements of dark matter’s self-interaction cross-section to the
model parameter σ /m. This parameter is the characteristic value of cross-section at which an
appropriately-sized cloud of standard model particles becomes optically thick. The top panel
shows the value of σ /m for different various substructure masses, assuming an NFW mass pro-
file and a mass-concentration relation from cosmological simulations (45). The bottom panel
demonstrates how a few of those values affect our measurement of the cross-section. The re-
sulting variation is sub-dominant to statistical error in our sample of clusters. We adopted a
value of σ /m = 6.5 ± 3 cm2
/g, corresponding to dark matter halos of M = 1014±1
M , and
propagated the uncertainty through to our final constraints.
13
25. −2 −1 0 1 2 3 4
0.000
0.002
0.004
0.006
0.008
0.010
0.012
0.014
−2 −1 0 1 2 3 4
σDM/m [ cm2
/g]
0.000
0.002
0.004
0.006
0.008
0.010
0.012
0.014
p(σDM/m)
Total Sample
Cold Gas
Hot Gas
Figure S7: The sensitivity of measurements of dark matter’s self-interaction cross-section to
the temperature of the gas against which dark matter’s trajectory is calibrated. We measured
the gas temperature from the X-ray spectra of our 72 systems, and split the sample in two: blue
data show substructures with gas temperature < 8 keV, and red data show substructures with
gas temperature > 8 keV. The constraining power of each sample is approximately
√
2 less than
that of the full sample, shown in grey, and no statistically significant difference is measured.
14
26. 0.0 0.5 1.0 1.5 2.0 2.5
r / r500
0.00
0.05
0.10
0.15
0.20
0.25
ρG/ρD
ΩB/ΩD (Planck 2013)
Density at position of sub−halo from mock data
Average density in mock data
Figure S8: The sensitivity of measurements of dark matter’s self-interaction cross-section to the
density of gas through which it is moving. The plot shows the gas fraction fgas = ρgas/ρDM
in simulated galaxy clusters (46), as a function of clustercentric radius. The solid line shows
the average fgas over 16 clusters, with the 1σ error on the mean given in grey. Triangles show
the measured fgas at the radius of substructures observable in mock 2D realisations of the 3D
simulations (only the inner ∼ 60% lie inside the HST field of view at the redshifts of the
observed systems). Our interpretation of the dark matter and gas trajectories as an interaction
cross-section, assumes that these are lower than the universal fraction ΩB/ΩD = 0.184 (33).
15
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