Assymetries in core_collapse_supernovae_from_maps_of_radioactive_ti_in_cassio...Sérgio Sacani
The document summarizes findings from observations of Cassiopeia A using the Nuclear Spectroscopic Telescope Array (NuSTAR).
1) NuSTAR detected two clear emission lines from the decay of radioactive titanium-44, confirming previous measurements of titanium-44 yield with high significance. The spatial distribution of titanium-44 emission shows it is clumpy and extended along the jet axis seen in X-ray images, with knots off the jet axis.
2) There is no correlation between the distribution of titanium-44 and iron detected by Chandra X-ray Observatory. This suggests much of the iron-rich ejecta has not been shock-heated and is "invisible", constraining models of the remnant.
The shadow _of_the_flying_saucer_a_very_low_temperature_for_large_dust_grainsSérgio Sacani
Os astrónomos usaram o ALMA e os telescópios do IRAM para fazer a primeira medição direta da temperatura dos grãos de poeira grandes situados nas regiões periféricas de um disco de formação planetária que se encontra em torno de uma estrela jovem. Ao observar de forma inovadora um objeto cujo nome informal é Disco Voador, os astrónomos descobriram que os grãos de poeira são muito mais frios do que o esperado: -266º Celsius. Este resultado surpreendente sugere que os modelos teóricos destes discos precisam de ser revistos.
Uma equipa internacional liderada por Stephane Guilloteau do Laboratoire d´Astrophysique de Bordeaux, França, mediu a temperatura de enormes grãos de poeira que se encontram em torno da jovem estrela 2MASS J16281370-2431391 na região de formação estelar Rho Ophiuchi, a cerca de 400 anos-luz de distância da Terra.
Esta estrela encontra-se rodeada por um disco de gás e poeira — chamado disco protoplanetário, uma vez que se encontra na fase inicial da formação de um sistema planetário. Este disco é visto de perfil quando observado a partir da Terra e a sua aparência em imagens no visível levou a que se lhe desse o nome informal de Disco Voador.
Os astrónomos utilizaram o ALMA para observar o brilho emitido pelas moléculas de monóxido de carbono no disco da 2MASS J16281370-2431391. As imagens revelaram-se extremamente nítidas e descobriu-se algo estranho — em alguns casos o sinal recebido era negativo. Normalmente um sinal negativo é fisicamente impossível, mas neste caso existe uma explicação, que leva a uma conclusão surpreendente.
Todo mundo sabe que os raios produzidos pela Estrela da Morte em Guerra nas Estrelas não pode existir na vida real, porém no universo existem fenômenos que as vezes conseguem superar até a mais surpreendente ficção.
A galáxia Pictor A, é um desses objetos que possuem fenômenos tão espetaculares quanto aqueles exibidos no cinema. Essa galáxia localiza-se a cerca de 500 milhões de anos-luz da Terra e possui um buraco negro supermassivo no seu centro. Uma grande quantidade de energia gravitacional é lançada, à medida que o material cai em direção ao horizonte de eventos, o ponto sem volta ao redor do buraco negro. Essa energia produz um enorme jato de partículas que viajam a uma velocidade próxima da velocidade da luz no espaço intergaláctico, chamado de jato relativístico.
Para obter imagens desse jato, os cientistas usaram o Observatório de Raios-X Chandra, da NASA várias vezes durante 15 anos. Os dados do Chandra, apresentados em azul nas imagens, foram combinados com os dados obtidos em ondas de rádio a partir do Australia Telescope Compact Array, e são aparesentados em vermelho nas imagens.
This document reports on evidence for spatial variation in the fine structure constant α from observations of quasar absorption spectra. A sample of 153 measurements from the ESO Very Large Telescope (VLT) probing a different region of the universe suggests α was larger in the past, opposite to previous findings from the Keck telescope. Combining the two datasets reveals a significant spatial dipole in α, with the maximum variation in the direction of right ascension 17.3 hours, declination -61 degrees. Detailed analysis found no systematic effects that could mimic this result.
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.
This document describes observations of Cepheid variables in the host galaxies of two Type Ia supernovae, SN 1995al in NGC 3021 and SN 2002fk in NGC 1309, using the Hubble Space Telescope. The observations aim to increase the sample of reliably calibrated supernovae to improve the measurement of the Hubble constant. New Cepheids were discovered, including many with periods over 60 days. Metallicity measurements of the galaxies' H II regions were also consistent with solar metallicity. The new data on the supernovae and Cepheids will help strengthen the distance ladder and reduce systematic uncertainties in the determination of the Hubble constant.
Detection of solar_like_oscillations_in_relies_of_the_milk_way_asteroseismolo...Sérgio Sacani
Asteroseismic constraints on K giants make it possible to infer radii, masses and ages of tens
of thousands of field stars. Tests against independent estimates of these properties are however
scarce, especially in the metal-poor regime. Here, we report the detection of solar-like
oscillations in 8 stars belonging to the red-giant branch and red-horizontal branch of the globular
cluster M4. The detections were made in photometric observations from the K2 Mission
during its Campaign 2. Making use of independent constraints on the distance, we estimate
masses of the 8 stars by utilising different combinations of seismic and non-seismic inputs.
When introducing a correction to the Δν scaling relation as suggested by stellar models, for
RGB stars we find excellent agreement with the expected masses from isochrone fitting, and
with a distance modulus derived using independent methods. The offset with respect to independent
masses is lower, or comparable with, the uncertainties on the average RGB mass
(4 − 10%, depending on the combination of constraints used). Our results lend confidence to
asteroseismic masses in the metal poor regime. We note that a larger sample will be needed
to allow more stringent tests to be made of systematic uncertainties in all the observables
(both seismic and non-seismic), and to explore the properties of RHB stars, and of different
populations in the cluster.
The open cluster_ngc6520_and_the_nearby_dark_molecular_cloud_barnard_86Sérgio Sacani
This document presents optical photometry and CO observations of the open cluster NGC 6520 and nearby dark molecular cloud Barnard 86. Analysis of the optical data finds the cluster radius is 1.0±0.5 arcmin, smaller than previous estimates. The cluster age is estimated to be 150±50 Myr with reddening of EB−V =0.42±0.10. The distance from the Sun is estimated to be 1900±100 pc, larger than previous estimates. CO observations are used to derive basic properties of Barnard 86 under the assumption it lies at the same distance as the cluster.
Assymetries in core_collapse_supernovae_from_maps_of_radioactive_ti_in_cassio...Sérgio Sacani
The document summarizes findings from observations of Cassiopeia A using the Nuclear Spectroscopic Telescope Array (NuSTAR).
1) NuSTAR detected two clear emission lines from the decay of radioactive titanium-44, confirming previous measurements of titanium-44 yield with high significance. The spatial distribution of titanium-44 emission shows it is clumpy and extended along the jet axis seen in X-ray images, with knots off the jet axis.
2) There is no correlation between the distribution of titanium-44 and iron detected by Chandra X-ray Observatory. This suggests much of the iron-rich ejecta has not been shock-heated and is "invisible", constraining models of the remnant.
The shadow _of_the_flying_saucer_a_very_low_temperature_for_large_dust_grainsSérgio Sacani
Os astrónomos usaram o ALMA e os telescópios do IRAM para fazer a primeira medição direta da temperatura dos grãos de poeira grandes situados nas regiões periféricas de um disco de formação planetária que se encontra em torno de uma estrela jovem. Ao observar de forma inovadora um objeto cujo nome informal é Disco Voador, os astrónomos descobriram que os grãos de poeira são muito mais frios do que o esperado: -266º Celsius. Este resultado surpreendente sugere que os modelos teóricos destes discos precisam de ser revistos.
Uma equipa internacional liderada por Stephane Guilloteau do Laboratoire d´Astrophysique de Bordeaux, França, mediu a temperatura de enormes grãos de poeira que se encontram em torno da jovem estrela 2MASS J16281370-2431391 na região de formação estelar Rho Ophiuchi, a cerca de 400 anos-luz de distância da Terra.
Esta estrela encontra-se rodeada por um disco de gás e poeira — chamado disco protoplanetário, uma vez que se encontra na fase inicial da formação de um sistema planetário. Este disco é visto de perfil quando observado a partir da Terra e a sua aparência em imagens no visível levou a que se lhe desse o nome informal de Disco Voador.
Os astrónomos utilizaram o ALMA para observar o brilho emitido pelas moléculas de monóxido de carbono no disco da 2MASS J16281370-2431391. As imagens revelaram-se extremamente nítidas e descobriu-se algo estranho — em alguns casos o sinal recebido era negativo. Normalmente um sinal negativo é fisicamente impossível, mas neste caso existe uma explicação, que leva a uma conclusão surpreendente.
Todo mundo sabe que os raios produzidos pela Estrela da Morte em Guerra nas Estrelas não pode existir na vida real, porém no universo existem fenômenos que as vezes conseguem superar até a mais surpreendente ficção.
A galáxia Pictor A, é um desses objetos que possuem fenômenos tão espetaculares quanto aqueles exibidos no cinema. Essa galáxia localiza-se a cerca de 500 milhões de anos-luz da Terra e possui um buraco negro supermassivo no seu centro. Uma grande quantidade de energia gravitacional é lançada, à medida que o material cai em direção ao horizonte de eventos, o ponto sem volta ao redor do buraco negro. Essa energia produz um enorme jato de partículas que viajam a uma velocidade próxima da velocidade da luz no espaço intergaláctico, chamado de jato relativístico.
Para obter imagens desse jato, os cientistas usaram o Observatório de Raios-X Chandra, da NASA várias vezes durante 15 anos. Os dados do Chandra, apresentados em azul nas imagens, foram combinados com os dados obtidos em ondas de rádio a partir do Australia Telescope Compact Array, e são aparesentados em vermelho nas imagens.
This document reports on evidence for spatial variation in the fine structure constant α from observations of quasar absorption spectra. A sample of 153 measurements from the ESO Very Large Telescope (VLT) probing a different region of the universe suggests α was larger in the past, opposite to previous findings from the Keck telescope. Combining the two datasets reveals a significant spatial dipole in α, with the maximum variation in the direction of right ascension 17.3 hours, declination -61 degrees. Detailed analysis found no systematic effects that could mimic this result.
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.
This document describes observations of Cepheid variables in the host galaxies of two Type Ia supernovae, SN 1995al in NGC 3021 and SN 2002fk in NGC 1309, using the Hubble Space Telescope. The observations aim to increase the sample of reliably calibrated supernovae to improve the measurement of the Hubble constant. New Cepheids were discovered, including many with periods over 60 days. Metallicity measurements of the galaxies' H II regions were also consistent with solar metallicity. The new data on the supernovae and Cepheids will help strengthen the distance ladder and reduce systematic uncertainties in the determination of the Hubble constant.
Detection of solar_like_oscillations_in_relies_of_the_milk_way_asteroseismolo...Sérgio Sacani
Asteroseismic constraints on K giants make it possible to infer radii, masses and ages of tens
of thousands of field stars. Tests against independent estimates of these properties are however
scarce, especially in the metal-poor regime. Here, we report the detection of solar-like
oscillations in 8 stars belonging to the red-giant branch and red-horizontal branch of the globular
cluster M4. The detections were made in photometric observations from the K2 Mission
during its Campaign 2. Making use of independent constraints on the distance, we estimate
masses of the 8 stars by utilising different combinations of seismic and non-seismic inputs.
When introducing a correction to the Δν scaling relation as suggested by stellar models, for
RGB stars we find excellent agreement with the expected masses from isochrone fitting, and
with a distance modulus derived using independent methods. The offset with respect to independent
masses is lower, or comparable with, the uncertainties on the average RGB mass
(4 − 10%, depending on the combination of constraints used). Our results lend confidence to
asteroseismic masses in the metal poor regime. We note that a larger sample will be needed
to allow more stringent tests to be made of systematic uncertainties in all the observables
(both seismic and non-seismic), and to explore the properties of RHB stars, and of different
populations in the cluster.
The open cluster_ngc6520_and_the_nearby_dark_molecular_cloud_barnard_86Sérgio Sacani
This document presents optical photometry and CO observations of the open cluster NGC 6520 and nearby dark molecular cloud Barnard 86. Analysis of the optical data finds the cluster radius is 1.0±0.5 arcmin, smaller than previous estimates. The cluster age is estimated to be 150±50 Myr with reddening of EB−V =0.42±0.10. The distance from the Sun is estimated to be 1900±100 pc, larger than previous estimates. CO observations are used to derive basic properties of Barnard 86 under the assumption it lies at the same distance as the cluster.
1) Researchers observed 15 transits of the exoplanet GJ 1214b using the Hubble Space Telescope to measure its transmission spectrum from 1.1 to 1.7 microns.
2) The transmission spectrum was featureless, inconsistent with cloud-free atmospheres dominated by water, methane, carbon monoxide, nitrogen, or carbon dioxide.
3) The most likely explanation for the featureless spectrum is the presence of high-altitude clouds in the planet's atmosphere, which block the transmission of stellar light through the lower atmosphere.
Supermassive black holes in galaxy centres can grow by the accretion
of gas, liberating enormous amounts of energy that might
regulate star formation on galaxy-wide scales1–3
. The nature of
gaseous fuel reservoirs that power black hole growth is nevertheless
largely unconstrained by observations, and is instead routinely
simplified as a smooth, spherical inflow of very hot gas
in accordance with the Bondi solution4
. Recent theory5–7 and
simulations8–10 instead predict that accretion can be dominated by
a stochastic, clumpy distribution of very cold molecular clouds,
though unambiguous observational support for this prediction remains
elusive. Here we show observational evidence for a cold,
clumpy accretion flow toward a supermassive black hole fuel reservoir
in the nucleus of the Abell 2597 Brightest Cluster Galaxy
(BCG), a nearby (z = 0.0821) giant elliptical galaxy surrounded
by a dense halo of hot plasma11–13. Under the right conditions,
thermal instabilities can precipitate from this hot gas, producing a
rain of cold clouds that fall toward the galaxy’s centre14, sustaining
star formation amid a kiloparsec-scale molecular nebula that inhabits
its core15. New interferometric sub-millimetre observations
show that these cold clouds also fuel black hole accretion, revealing
“shadows” cast by molecular clouds as they move inward at ∼ 300
km s−1
toward the active supermassive black hole in the galaxy
centre, which serves as a bright backlight. Corroborating evidence
from prior observations16 of warmer atomic gas at extremely high
spatial resolution17, along with simple arguments based on geometry
and probability, indicates that these clouds are within the innermost
hundred parsecs of the black hole, and falling closer toward
it
Inverse Compton cooling limits the brightness temperature of the radiating plasma to a maximum of
1011.5 K. Relativistic boosting can increase its observed value, but apparent brightness temperatures
much in excess of 1013 K are inaccessible using ground-based very long baseline interferometry (VLBI)
at any wavelength. We present observations of the quasar 3C 273, made with the space VLBI mission
RadioAstron on baselines up to 171,000 km, which directly reveal the presence of angular structure as
small as 26 µas (2.7 light months) and brightness temperature in excess of 1013 K. These measurements
challenge our understanding of the non-thermal continuum emission in the vicinity of supermassive
black holes and require a much higher Doppler factor than what is determined from jet apparent
kinematics.
Keywords: galaxies: active — galaxies: jets — radio continuum: galaxies — techniques: interferometric
— quasars: individual (3C 273)
This document summarizes research on determining temperatures, luminosities, and masses of the coldest known brown dwarfs. The key findings are:
1) Precise distances were measured for a sample of late-T and Y dwarfs using Spitzer Space Telescope astrometry, allowing accurate calculation of absolute fluxes, luminosities, and temperatures.
2) Y0 dwarfs were found to have temperatures of 400-450 K, significantly warmer than previous estimates, and masses of 5-20 times Jupiter's mass.
3) While having similar temperatures, Y dwarfs showed diverse spectral energy distributions, suggesting temperature alone does not determine spectra. Physical properties like gravity, clouds and chemistry also influence spectra.
This document discusses using future full-sky galaxy surveys from space telescopes to probe initial conditions and constrain primordial non-Gaussianity. It proposes launching a space telescope called SPHEREx to conduct a full-sky galaxy spectroscopy survey. This would allow probing the horizon-scale clustering needed to constrain the non-Gaussianity parameter fNL using both the galaxy power spectrum and bispectrum. Current forecasts suggest SPHEREx could achieve an uncertainty of σ(fNL) ~ 0.8 from the power spectrum alone and σ(fNL) ~ 0.2 when also including the bispectrum. However, challenges remain in applying photometric redshift indicators and understanding contributions to the squeezed bispectrum at higher orders.
Magnetic interaction of_a_super_cme_with_the_earths_magnetosphere_scenario_fo...Sérgio Sacani
Solar eruptions, known as Coronal Mass Ejections (CMEs), are
frequently observed on our Sun. Recent Kepler observations of super
ares
on G-type stars have implied that so called super-CMEs, possessing kinetic
energies 10 times of the most powerful CME event ever observed on the Sun,
could be produced with a frequency of 1 event per 800-2000 yr on solar-
like slowly rotating stars. We have performed a 3D time-dependent global
magnetohydrodynamic simulation of the magnetic interaction of such a CME
cloud with the Earth's magnetosphere. We calculated the global structure
of the perturbed magnetosphere and derive the latitude of the open-closed
magnetic eld boundary. We also estimated energy
uxes penetrating the
Earth's ionosphere and discuss the consequences of energetic particle
uxes
on biological systems on early Earth.
Too much pasta_for_pulsars_to_spin_downSérgio Sacani
This document summarizes a study investigating why no isolated X-ray pulsars have been observed with spin periods longer than 12 seconds. The researchers suggest this is due to a highly resistive layer in the inner crust of neutron stars, which is expected to be in a state called "nuclear pasta". Nuclear pasta has an irregular structure that increases electrical resistivity, limiting the spin-down of pulsars. Modeling the long-term magnetic field evolution incorporating a resistive nuclear pasta layer successfully reproduced the observed 12 second period limit. The results provide the first potential observational evidence for the existence of nuclear pasta in neutron star crusts.
The Internal Structure of Asteroid (25143) Itokawa as Revealed by Detection o...WellingtonRodrigues2014
- The authors detected an acceleration in the rotation rate of asteroid (25143) Itokawa through photometric observations spanning 2001 to 2013.
- By measuring rotational phase offsets between observed and modeled lightcurves, they found a YORP acceleration of 3.54 ± 0.38 × 10−8 rad day−2, equivalent to a decrease in the asteroid's rotation period of about 45 ms per year.
- Thermophysical modeling of the detailed shape model from the Hayabusa spacecraft could not reconcile the observed YORP strength unless the asteroid's center of mass is shifted by about 21 m along its long axis. This suggests Itokawa has two components with different densities that merged, either from a
Dissecting x ray_emitting_gas_around_the_center_of_our_galaxySérgio Sacani
1) The Chandra X-ray Observatory was used to observe the supermassive black hole at the center of the Milky Way, Sgr A*, for a total of 3 megaseconds.
2) The observations revealed extended X-ray emission around Sgr A* that aligns spatially with a surrounding disk of massive stars.
3) Spectral analysis ruled out low-mass stars as the origin of the X-ray emission and instead found evidence that the emission is from a radiatively inefficient accretion flow onto the black hole, with an outflow present.
The ASTRODEEP Frontier Fields catalogues II. Photometric redshifts and rest f...Sérgio Sacani
This document describes a public release of photometric redshifts and galaxy properties from multi-wavelength data in the Abell-2744 and MACS-J0416 galaxy cluster fields observed as part of the Frontier Fields program. Photometric redshifts were estimated using six different methods and have an accuracy of 3-5%. Accounting for gravitational lensing magnification, the H-band number counts agree with CANDELS at bright magnitudes but extend to intrinsically fainter galaxies of H=32-33. The Frontier Fields data allow probing galaxy stellar masses 0.5-1.5 dex lower than in wide fields, including sources with masses of 107-108 solar masses at z>5. Star formation rates can be detected 1
A 2 4_determination_of_the_local_value_of_the_hubble_constantSérgio Sacani
We use the Wide Field Camera 3 (WFC3) on the Hubble Space Telescope (HST) to
reduce the uncertainty in the local value of the Hubble constant from 3.3% to 2.4%.
The bulk of this improvement comes from new, near-infrared observations of Cepheid
variables in 11 host galaxies of recent type Ia supernovae (SNe Ia), more than doubling
the sample of reliable SNe Ia having a Cepheid-calibrated distance to a total of 19; these
in turn leverage the magnitude-redshift relation based on 300 SNe Ia at z <0.15. All
19 hosts as well as the megamaser system NGC4258 have been observed with WFC3
in the optical and near-infrared, thus nullifying cross-instrument zeropoint errors in the
relative distance estimates from Cepheids. Other noteworthy improvements include a
33% reduction in the systematic uncertainty in the maser distance to NGC4258, a larger
sample of Cepheids in the Large Magellanic Cloud (LMC), a more robust distance to
the LMC based on late-type detached eclipsing binaries (DEBs), HST observations of
Cepheids in M31, and new HST-based trigonometric parallaxes for Milky Way (MW)
Cepheids.
Serendipitous discovery of an extended xray jet without a radio counterpart i...Sérgio Sacani
A recent Chandra observation of the nearby galaxy cluster Abell 585 has led to the discovery of
an extended X-ray jet associated with the high-redshift background quasar B3 0727+409, a luminous
radio source at redshift z = 2:5. This is one of only few examples of high-redshift X-ray jets known
to date. It has a clear extension of about 1200, corresponding to a projected length of 100 kpc, with
a possible hot spot located 3500 from the quasar. The archival high resolution VLA maps surprisingly
reveal no extended jet emission, except for one knot about 1:400 from the quasar. The high X-ray to
radio luminosity ratio for this source appears consistent with the / (1 + z)4 amplication expected
from the inverse Compton radiative model. This serendipitous discovery may signal the existence
of an entire population of similar systems with bright X-ray and faint radio jets at high redshift, a
selection bias which must be accounted for when drawing any conclusions about the redshift evolution
of jet properties and indeed about the cosmological evolution of supermassive black holes and active
galactic nuclei in general.
An elevation of 0.1 light-seconds for the optical jet base in an accreting Ga...Sérgio Sacani
Relativistic plasma jets are observed in many systems that
host accreting black holes. According to theory, coiled magnetic
fields close to the black hole accelerate and collimate the
plasma, leading to a jet being launched1–3. Isolating emission
from this acceleration and collimation zone is key to measuring
its size and understanding jet formation physics. But this
is challenging because emission from the jet base cannot
easily be disentangled from other accreting components. Here,
we show that rapid optical flux variations from an accreting
Galactic black-hole binary are delayed with respect to X-rays
radiated from close to the black hole by about 0.1 seconds, and
that this delayed signal appears together with a brightening
radio jet. The origin of these subsecond optical variations
has hitherto been controversial4–8. Not only does our work
strongly support a jet origin for the optical variations but it
also sets a characteristic elevation of ≲ 103 Schwarzschild
radii for the main inner optical emission zone above the black
hole9, constraining both internal shock10 and magnetohydrodynamic11
models. Similarities with blazars12,13 suggest that jet
structure and launching physics could potentially be unified
under mass-invariant models. Two of the best-studied jetted
black-hole binaries show very similar optical lags8,14,15, so this
size scale may be a defining feature of such systems.
The characterization of_the_gamma_ray_signal_from_the_central_milk_way_a_comp...Sérgio Sacani
This document analyzes the gamma-ray signal from the central Milky Way that is consistent with emission from annihilating dark matter particles. The authors re-examine Fermi data using cuts on an event parameter to improve gamma-ray maps and more easily separate components. They find the GeV excess is robust and well-fit by a 36-51 GeV dark matter particle annihilating to bottom quarks with a cross section of 1-3×10−26 cm3/s. The signal extends over 10 degrees from the Galactic Center and is spherically symmetric, disfavoring explanations from millisecond pulsars or gas interactions.
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.
This study analyzed transit observations of the Neptune-mass exoplanet GJ 436b taken with the Hubble Space Telescope. The transmission spectrum was found to be featureless, ruling out cloud-free hydrogen-dominated atmosphere models with high significance. The flat transmission spectrum is consistent with either an atmosphere containing high-altitude clouds located at a pressure of around 1 millibar, or a relatively hydrogen-poor atmosphere with 3% hydrogen and helium by mass. Bayesian atmospheric modeling showed that cloudy hydrogen-dominated or high-metallicity hydrogen-poor atmospheres provide the best fits to the data. Further observations are needed to distinguish between these scenarios.
Evidence for the_thermal_sunyaev-zeldovich_effect_associated_with_quasar_feed...Sérgio Sacani
Using a radio-quiet subsample of the Sloan Digital Sky Survey spectroscopic quasar
catalogue, spanning redshifts 0.5–3.5, we derive the mean millimetre and far-infrared
quasar spectral energy distributions (SEDs) via a stacking analysis of Atacama Cosmology
Telescope and Herschel-Spectral and Photometric Imaging REceiver data. We
constrain the form of the far-infrared emission and find 3σ–4σ evidence for the thermal
Sunyaev-Zel’dovich (SZ) effect, characteristic of a hot ionized gas component with
thermal energy (6.2 ± 1.7) × 1060 erg. This amount of thermal energy is greater than
expected assuming only hot gas in virial equilibrium with the dark matter haloes of
(1 − 5) × 1012h
−1M that these systems are expected to occupy, though the highest
quasar mass estimates found in the literature could explain a large fraction of this
energy. Our measurements are consistent with quasars depositing up to (14.5±3.3) τ
−1
8
per cent of their radiative energy into their circumgalactic environment if their typical
period of quasar activity is τ8 × 108 yr. For high quasar host masses, ∼ 1013h
−1M,
this percentage will be reduced. Furthermore, the uncertainty on this percentage is
only statistical and additional systematic uncertainties enter at the 40 per cent level.
The SEDs are dust dominated in all bands and we consider various models for dust
emission. While sufficiently complex dust models can obviate the SZ effect, the SZ
interpretation remains favoured at the 3σ–4σ level for most models.
Galaxy dynamics and the mass density of the universeSérgio Sacani
Dynamical evidence accumulated over the
past 20 years has convinced astronomers that luminous matter
in a spiral galaxy constitutes no more than 10% of the mass of
a galaxy. An additional 90% is inferred by its gravitational
effect on luminous material. Here I review recent observations
concerning the distribution of luminous and nonluminous
matter in the Milky Way, in galaxies, and in galaxy clusters.
Observations of neutral hydrogen disks, some extending in
radius several times the optical disk, confirm that a massive
dark halo is a major component of virtually every spiral. A
recent surprise has been the discovery that stellar and gas
motions in ellipticals are enormously complex. To date, only for
a few spheroidal galaxies do the velocities extend far enough to
probe the outer mass distribution. But the diverse kinematics
of inner cores, peripheral to deducing the overall mass distribution,
offer additional evidence that ellipticals have acquired
gas-rich systems after initial formation. Dynamical results are
consistent with a low-density universe, in which the required
dark matter could be baryonic. On smallest scales of galaxies
[10 kiloparsec (kpc); H. = 50 kmsec'lmegaparsec'11 the
luminous matter constitutes only 1% of the closure density. On
scales greater than binary galaxies (i.e., .100 kpc) all systems
indicate a density -10% of the closure density, a density
consistent with the low baryon density in the universe. If
large-scale motions in the universe require a higher mass
density, these motions would constitute the first dynamical
evidence for nonbaryonic matter in a universe of higher
density.
A highly magnetized twin-jet base pinpoints a supermassive black holeSérgio Sacani
Supermassive black holes (SMBH) are essential for the production of jets in radio-loud active galactic nuclei (AGN). Theoretical
models based on (Blandford & Znajek 1977, MNRAS, 179, 433) extract the rotational energy from a Kerr black hole, which could
be the case for NGC1052, to launch these jets. This requires magnetic fields on the order of 103 G to 104 G. We imaged the vicinity
of the SMBH of the AGN NGC1052 with the Global Millimetre VLBI Array and found a bright and compact central feature that is
smaller than 1.9 light days (100 Schwarzschild radii) in radius. Interpreting this as a blend of the unresolved jet bases, we derive the
magnetic field at 1 Schwarzschild radius to lie between 200 G and 8:3 104 G consistent with Blandford & Znajek models.
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)
1) Researchers observed 15 transits of the exoplanet GJ 1214b using the Hubble Space Telescope to measure its transmission spectrum from 1.1 to 1.7 microns.
2) The transmission spectrum was featureless, inconsistent with cloud-free atmospheres dominated by water, methane, carbon monoxide, nitrogen, or carbon dioxide.
3) The most likely explanation for the featureless spectrum is the presence of high-altitude clouds in the planet's atmosphere, which block the transmission of stellar light through the lower atmosphere.
Supermassive black holes in galaxy centres can grow by the accretion
of gas, liberating enormous amounts of energy that might
regulate star formation on galaxy-wide scales1–3
. The nature of
gaseous fuel reservoirs that power black hole growth is nevertheless
largely unconstrained by observations, and is instead routinely
simplified as a smooth, spherical inflow of very hot gas
in accordance with the Bondi solution4
. Recent theory5–7 and
simulations8–10 instead predict that accretion can be dominated by
a stochastic, clumpy distribution of very cold molecular clouds,
though unambiguous observational support for this prediction remains
elusive. Here we show observational evidence for a cold,
clumpy accretion flow toward a supermassive black hole fuel reservoir
in the nucleus of the Abell 2597 Brightest Cluster Galaxy
(BCG), a nearby (z = 0.0821) giant elliptical galaxy surrounded
by a dense halo of hot plasma11–13. Under the right conditions,
thermal instabilities can precipitate from this hot gas, producing a
rain of cold clouds that fall toward the galaxy’s centre14, sustaining
star formation amid a kiloparsec-scale molecular nebula that inhabits
its core15. New interferometric sub-millimetre observations
show that these cold clouds also fuel black hole accretion, revealing
“shadows” cast by molecular clouds as they move inward at ∼ 300
km s−1
toward the active supermassive black hole in the galaxy
centre, which serves as a bright backlight. Corroborating evidence
from prior observations16 of warmer atomic gas at extremely high
spatial resolution17, along with simple arguments based on geometry
and probability, indicates that these clouds are within the innermost
hundred parsecs of the black hole, and falling closer toward
it
Inverse Compton cooling limits the brightness temperature of the radiating plasma to a maximum of
1011.5 K. Relativistic boosting can increase its observed value, but apparent brightness temperatures
much in excess of 1013 K are inaccessible using ground-based very long baseline interferometry (VLBI)
at any wavelength. We present observations of the quasar 3C 273, made with the space VLBI mission
RadioAstron on baselines up to 171,000 km, which directly reveal the presence of angular structure as
small as 26 µas (2.7 light months) and brightness temperature in excess of 1013 K. These measurements
challenge our understanding of the non-thermal continuum emission in the vicinity of supermassive
black holes and require a much higher Doppler factor than what is determined from jet apparent
kinematics.
Keywords: galaxies: active — galaxies: jets — radio continuum: galaxies — techniques: interferometric
— quasars: individual (3C 273)
This document summarizes research on determining temperatures, luminosities, and masses of the coldest known brown dwarfs. The key findings are:
1) Precise distances were measured for a sample of late-T and Y dwarfs using Spitzer Space Telescope astrometry, allowing accurate calculation of absolute fluxes, luminosities, and temperatures.
2) Y0 dwarfs were found to have temperatures of 400-450 K, significantly warmer than previous estimates, and masses of 5-20 times Jupiter's mass.
3) While having similar temperatures, Y dwarfs showed diverse spectral energy distributions, suggesting temperature alone does not determine spectra. Physical properties like gravity, clouds and chemistry also influence spectra.
This document discusses using future full-sky galaxy surveys from space telescopes to probe initial conditions and constrain primordial non-Gaussianity. It proposes launching a space telescope called SPHEREx to conduct a full-sky galaxy spectroscopy survey. This would allow probing the horizon-scale clustering needed to constrain the non-Gaussianity parameter fNL using both the galaxy power spectrum and bispectrum. Current forecasts suggest SPHEREx could achieve an uncertainty of σ(fNL) ~ 0.8 from the power spectrum alone and σ(fNL) ~ 0.2 when also including the bispectrum. However, challenges remain in applying photometric redshift indicators and understanding contributions to the squeezed bispectrum at higher orders.
Magnetic interaction of_a_super_cme_with_the_earths_magnetosphere_scenario_fo...Sérgio Sacani
Solar eruptions, known as Coronal Mass Ejections (CMEs), are
frequently observed on our Sun. Recent Kepler observations of super
ares
on G-type stars have implied that so called super-CMEs, possessing kinetic
energies 10 times of the most powerful CME event ever observed on the Sun,
could be produced with a frequency of 1 event per 800-2000 yr on solar-
like slowly rotating stars. We have performed a 3D time-dependent global
magnetohydrodynamic simulation of the magnetic interaction of such a CME
cloud with the Earth's magnetosphere. We calculated the global structure
of the perturbed magnetosphere and derive the latitude of the open-closed
magnetic eld boundary. We also estimated energy
uxes penetrating the
Earth's ionosphere and discuss the consequences of energetic particle
uxes
on biological systems on early Earth.
Too much pasta_for_pulsars_to_spin_downSérgio Sacani
This document summarizes a study investigating why no isolated X-ray pulsars have been observed with spin periods longer than 12 seconds. The researchers suggest this is due to a highly resistive layer in the inner crust of neutron stars, which is expected to be in a state called "nuclear pasta". Nuclear pasta has an irregular structure that increases electrical resistivity, limiting the spin-down of pulsars. Modeling the long-term magnetic field evolution incorporating a resistive nuclear pasta layer successfully reproduced the observed 12 second period limit. The results provide the first potential observational evidence for the existence of nuclear pasta in neutron star crusts.
The Internal Structure of Asteroid (25143) Itokawa as Revealed by Detection o...WellingtonRodrigues2014
- The authors detected an acceleration in the rotation rate of asteroid (25143) Itokawa through photometric observations spanning 2001 to 2013.
- By measuring rotational phase offsets between observed and modeled lightcurves, they found a YORP acceleration of 3.54 ± 0.38 × 10−8 rad day−2, equivalent to a decrease in the asteroid's rotation period of about 45 ms per year.
- Thermophysical modeling of the detailed shape model from the Hayabusa spacecraft could not reconcile the observed YORP strength unless the asteroid's center of mass is shifted by about 21 m along its long axis. This suggests Itokawa has two components with different densities that merged, either from a
Dissecting x ray_emitting_gas_around_the_center_of_our_galaxySérgio Sacani
1) The Chandra X-ray Observatory was used to observe the supermassive black hole at the center of the Milky Way, Sgr A*, for a total of 3 megaseconds.
2) The observations revealed extended X-ray emission around Sgr A* that aligns spatially with a surrounding disk of massive stars.
3) Spectral analysis ruled out low-mass stars as the origin of the X-ray emission and instead found evidence that the emission is from a radiatively inefficient accretion flow onto the black hole, with an outflow present.
The ASTRODEEP Frontier Fields catalogues II. Photometric redshifts and rest f...Sérgio Sacani
This document describes a public release of photometric redshifts and galaxy properties from multi-wavelength data in the Abell-2744 and MACS-J0416 galaxy cluster fields observed as part of the Frontier Fields program. Photometric redshifts were estimated using six different methods and have an accuracy of 3-5%. Accounting for gravitational lensing magnification, the H-band number counts agree with CANDELS at bright magnitudes but extend to intrinsically fainter galaxies of H=32-33. The Frontier Fields data allow probing galaxy stellar masses 0.5-1.5 dex lower than in wide fields, including sources with masses of 107-108 solar masses at z>5. Star formation rates can be detected 1
A 2 4_determination_of_the_local_value_of_the_hubble_constantSérgio Sacani
We use the Wide Field Camera 3 (WFC3) on the Hubble Space Telescope (HST) to
reduce the uncertainty in the local value of the Hubble constant from 3.3% to 2.4%.
The bulk of this improvement comes from new, near-infrared observations of Cepheid
variables in 11 host galaxies of recent type Ia supernovae (SNe Ia), more than doubling
the sample of reliable SNe Ia having a Cepheid-calibrated distance to a total of 19; these
in turn leverage the magnitude-redshift relation based on 300 SNe Ia at z <0.15. All
19 hosts as well as the megamaser system NGC4258 have been observed with WFC3
in the optical and near-infrared, thus nullifying cross-instrument zeropoint errors in the
relative distance estimates from Cepheids. Other noteworthy improvements include a
33% reduction in the systematic uncertainty in the maser distance to NGC4258, a larger
sample of Cepheids in the Large Magellanic Cloud (LMC), a more robust distance to
the LMC based on late-type detached eclipsing binaries (DEBs), HST observations of
Cepheids in M31, and new HST-based trigonometric parallaxes for Milky Way (MW)
Cepheids.
Serendipitous discovery of an extended xray jet without a radio counterpart i...Sérgio Sacani
A recent Chandra observation of the nearby galaxy cluster Abell 585 has led to the discovery of
an extended X-ray jet associated with the high-redshift background quasar B3 0727+409, a luminous
radio source at redshift z = 2:5. This is one of only few examples of high-redshift X-ray jets known
to date. It has a clear extension of about 1200, corresponding to a projected length of 100 kpc, with
a possible hot spot located 3500 from the quasar. The archival high resolution VLA maps surprisingly
reveal no extended jet emission, except for one knot about 1:400 from the quasar. The high X-ray to
radio luminosity ratio for this source appears consistent with the / (1 + z)4 amplication expected
from the inverse Compton radiative model. This serendipitous discovery may signal the existence
of an entire population of similar systems with bright X-ray and faint radio jets at high redshift, a
selection bias which must be accounted for when drawing any conclusions about the redshift evolution
of jet properties and indeed about the cosmological evolution of supermassive black holes and active
galactic nuclei in general.
An elevation of 0.1 light-seconds for the optical jet base in an accreting Ga...Sérgio Sacani
Relativistic plasma jets are observed in many systems that
host accreting black holes. According to theory, coiled magnetic
fields close to the black hole accelerate and collimate the
plasma, leading to a jet being launched1–3. Isolating emission
from this acceleration and collimation zone is key to measuring
its size and understanding jet formation physics. But this
is challenging because emission from the jet base cannot
easily be disentangled from other accreting components. Here,
we show that rapid optical flux variations from an accreting
Galactic black-hole binary are delayed with respect to X-rays
radiated from close to the black hole by about 0.1 seconds, and
that this delayed signal appears together with a brightening
radio jet. The origin of these subsecond optical variations
has hitherto been controversial4–8. Not only does our work
strongly support a jet origin for the optical variations but it
also sets a characteristic elevation of ≲ 103 Schwarzschild
radii for the main inner optical emission zone above the black
hole9, constraining both internal shock10 and magnetohydrodynamic11
models. Similarities with blazars12,13 suggest that jet
structure and launching physics could potentially be unified
under mass-invariant models. Two of the best-studied jetted
black-hole binaries show very similar optical lags8,14,15, so this
size scale may be a defining feature of such systems.
The characterization of_the_gamma_ray_signal_from_the_central_milk_way_a_comp...Sérgio Sacani
This document analyzes the gamma-ray signal from the central Milky Way that is consistent with emission from annihilating dark matter particles. The authors re-examine Fermi data using cuts on an event parameter to improve gamma-ray maps and more easily separate components. They find the GeV excess is robust and well-fit by a 36-51 GeV dark matter particle annihilating to bottom quarks with a cross section of 1-3×10−26 cm3/s. The signal extends over 10 degrees from the Galactic Center and is spherically symmetric, disfavoring explanations from millisecond pulsars or gas interactions.
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.
This study analyzed transit observations of the Neptune-mass exoplanet GJ 436b taken with the Hubble Space Telescope. The transmission spectrum was found to be featureless, ruling out cloud-free hydrogen-dominated atmosphere models with high significance. The flat transmission spectrum is consistent with either an atmosphere containing high-altitude clouds located at a pressure of around 1 millibar, or a relatively hydrogen-poor atmosphere with 3% hydrogen and helium by mass. Bayesian atmospheric modeling showed that cloudy hydrogen-dominated or high-metallicity hydrogen-poor atmospheres provide the best fits to the data. Further observations are needed to distinguish between these scenarios.
Evidence for the_thermal_sunyaev-zeldovich_effect_associated_with_quasar_feed...Sérgio Sacani
Using a radio-quiet subsample of the Sloan Digital Sky Survey spectroscopic quasar
catalogue, spanning redshifts 0.5–3.5, we derive the mean millimetre and far-infrared
quasar spectral energy distributions (SEDs) via a stacking analysis of Atacama Cosmology
Telescope and Herschel-Spectral and Photometric Imaging REceiver data. We
constrain the form of the far-infrared emission and find 3σ–4σ evidence for the thermal
Sunyaev-Zel’dovich (SZ) effect, characteristic of a hot ionized gas component with
thermal energy (6.2 ± 1.7) × 1060 erg. This amount of thermal energy is greater than
expected assuming only hot gas in virial equilibrium with the dark matter haloes of
(1 − 5) × 1012h
−1M that these systems are expected to occupy, though the highest
quasar mass estimates found in the literature could explain a large fraction of this
energy. Our measurements are consistent with quasars depositing up to (14.5±3.3) τ
−1
8
per cent of their radiative energy into their circumgalactic environment if their typical
period of quasar activity is τ8 × 108 yr. For high quasar host masses, ∼ 1013h
−1M,
this percentage will be reduced. Furthermore, the uncertainty on this percentage is
only statistical and additional systematic uncertainties enter at the 40 per cent level.
The SEDs are dust dominated in all bands and we consider various models for dust
emission. While sufficiently complex dust models can obviate the SZ effect, the SZ
interpretation remains favoured at the 3σ–4σ level for most models.
Galaxy dynamics and the mass density of the universeSérgio Sacani
Dynamical evidence accumulated over the
past 20 years has convinced astronomers that luminous matter
in a spiral galaxy constitutes no more than 10% of the mass of
a galaxy. An additional 90% is inferred by its gravitational
effect on luminous material. Here I review recent observations
concerning the distribution of luminous and nonluminous
matter in the Milky Way, in galaxies, and in galaxy clusters.
Observations of neutral hydrogen disks, some extending in
radius several times the optical disk, confirm that a massive
dark halo is a major component of virtually every spiral. A
recent surprise has been the discovery that stellar and gas
motions in ellipticals are enormously complex. To date, only for
a few spheroidal galaxies do the velocities extend far enough to
probe the outer mass distribution. But the diverse kinematics
of inner cores, peripheral to deducing the overall mass distribution,
offer additional evidence that ellipticals have acquired
gas-rich systems after initial formation. Dynamical results are
consistent with a low-density universe, in which the required
dark matter could be baryonic. On smallest scales of galaxies
[10 kiloparsec (kpc); H. = 50 kmsec'lmegaparsec'11 the
luminous matter constitutes only 1% of the closure density. On
scales greater than binary galaxies (i.e., .100 kpc) all systems
indicate a density -10% of the closure density, a density
consistent with the low baryon density in the universe. If
large-scale motions in the universe require a higher mass
density, these motions would constitute the first dynamical
evidence for nonbaryonic matter in a universe of higher
density.
A highly magnetized twin-jet base pinpoints a supermassive black holeSérgio Sacani
Supermassive black holes (SMBH) are essential for the production of jets in radio-loud active galactic nuclei (AGN). Theoretical
models based on (Blandford & Znajek 1977, MNRAS, 179, 433) extract the rotational energy from a Kerr black hole, which could
be the case for NGC1052, to launch these jets. This requires magnetic fields on the order of 103 G to 104 G. We imaged the vicinity
of the SMBH of the AGN NGC1052 with the Global Millimetre VLBI Array and found a bright and compact central feature that is
smaller than 1.9 light days (100 Schwarzschild radii) in radius. Interpreting this as a blend of the unresolved jet bases, we derive the
magnetic field at 1 Schwarzschild radius to lie between 200 G and 8:3 104 G consistent with Blandford & Znajek models.
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)
The nonmagnetic nucleus_of_comet_67_p_churyumov_gerasimenkoSérgio Sacani
Artigo descreve como a sonda Rosetta e o módulo Philae descobriram que o cometa Churyumov-Gerasimenko não é magnetizado, contrariando uma teoria da formação do Sistema Solar.
The puzzling source_in_ngc6388_a_possible_planetary_tidal_disruption_eventSérgio Sacani
Artigo descreve a descoberta da destruição de um planeta ao passar próximo a uma estrela do tipo anã branca presente dentro do aglomerado globular de estrelas NGC 6388. Para isso os astrônomos utilizaram um arsenal de telescópios.
Artigo descreve a descoberta do exoplaneta HATS-6b, um exoplaneta parecido com Saturno, porém pesado como Júpiter ao redor de uma estrela anã-M, o tipo de estrela mais abundante na nossa galáxia.
Small scatter and_nearly_isothermal_mass_profiles_to_four_half_light_radii_fr...Sérgio Sacani
This document summarizes the results of a study analyzing the total mass density profiles of 14 early-type galaxies using two-dimensional stellar kinematic data out to large radii of 2-6 half-light radii. The study finds that the total density profiles are well described by a nearly-isothermal power law with density proportional to radius from 0.1 to at least 4 half-light radii. The average logarithmic slope is -2.19 with a small scatter of only 0.11. This places tight constraints on galaxy formation models and illustrates the power of extended two-dimensional stellar kinematic observations.
The pillars of_creation_revisited_with_muse_gas_kinematics_and_high_mass_stel...Sérgio Sacani
The document discusses observations of the Pillars of Creation in the Eagle Nebula using integral field spectroscopy from the MUSE instrument on the VLT. For the first time, the study maps physical parameters like extinction, density, temperature, and velocity across the pillars. The data show that the pillar tips have high densities and are being photoevaporated by the massive stars in NGC 6611. The kinematics indicate a blueshifted photoevaporative flow, consistent with simulations. The 3D geometry of the pillars is inferred, with some in front of and some behind the ionizing stars. A previously unknown outflow is detected from the middle pillar, suggesting an embedded protostar.
A spectroscopic redshift_measurement_for_a_luminous_lyman_break_galaxy_at_z _...Sérgio Sacani
This document presents the spectroscopic confirmation of a luminous Lyman break galaxy (LBG) at a redshift of z = 7.7302 ± 0.0006, as observed using the MOSFIRE instrument on the Keck I telescope. The galaxy, named EGS-zs8-1, was pre-selected as a promising candidate for spectroscopic follow-up based on its bright apparent magnitude of H = 25.0 and very red Spitzer/IRAC colors suggestive of strong emission lines. Spectroscopic observations revealed a clear detection of the Lyman-alpha emission line at a observed wavelength of 1.06 microns, reliably confirming the high photometric redshift of z~7.7. Analysis of the
The broad lined_type_ic_sn_2012_ap_and_the_nature_of_relatvistic_supernovae_l...Sérgio Sacani
Artigo mostra como os astrônomos deduziram que a supernova SN 2012ap, é o elo perdido que faltava para a construção completa da árvore genealógica das supernovas.
Detection of a_supervoid_aligned_with_the_cold_spot_of_the_cosmic_microwave_b...Sérgio Sacani
This study uses infrared galaxy data from WISE and 2MASS surveys matched with optical data from the Pan-STARRS1 survey to search for a supervoid in the direction of the cosmic microwave background cold spot. Radial galaxy density profiles centered on the cold spot show a large underdensity extending over tens of degrees. Counts in photometric redshift bins within radii of 5 and 15 degrees show significantly low galaxy densities, at 5-6 sigma detection levels. This is consistent with a large 220 Mpc supervoid with an average density contrast of -0.14, centered at a redshift of 0.22. Such a supervoid could plausibly explain the observed cold spot in the cosmic microwave background.
The document summarizes findings from orbital magnetic field measurements taken by the MESSENGER spacecraft around Mercury. Key points:
1) Remanent magnetization has been detected in Mercury's crust, providing evidence that Mercury had a dynamo-generated magnetic field early in its history.
2) The magnetization is estimated to have an average age of 3.7-3.9 billion years, based on its presence across diverse terrain including the youngest volcanic deposits on Mercury.
3) Ancient field strengths that could have produced the observed magnetization range from Mercury's current dipole field strength to values similar to Earth's ancient field.
This document summarizes a study that identified 195 compact elliptical galaxies across different environments using data from optical and ultraviolet sky surveys. The researchers constructed the sample by selecting galaxies that were outliers from the universal color-magnitude relation and had small sizes and high stellar velocity dispersions based on spectral modeling. They found that 7 of the galaxies were isolated, not belonging to any known galaxy groups. For these isolated galaxies, the researchers identified possible host galaxies located up to 3.3 Mpc away. The stellar populations of the isolated compact elliptical galaxies were found to be similar to those in galaxy groups and clusters, suggesting a common formation mechanism.
This document presents evidence that massive galaxies at redshift 2.2 (~3 billion years after the Big Bang) undergo an "inside-out quenching" process, where star formation is quenched first in the inner regions and later in the outer disks. High-resolution observations of 22 star-forming galaxies show that the most massive galaxies already have dense bulges similar to local spheroids, while still actively forming stars in their outer disks. The data suggests star formation is suppressed from the inside out on timescales of less than 1 Gyr in the centers and up to a few Gyr in the outer disks, as an "inside-out quenching wave" propagates through the galaxies. This provides insights into how
Detection of an_unindentified_emission_line_in_the_stacked_x_ray_spectrum_of_...Sérgio Sacani
1. Researchers detected a previously unknown emission line in the stacked X-ray spectrum of 73 galaxy clusters observed by XMM-Newton. 2. The line was detected at an energy of 3.55-3.57 keV and was seen independently in subsamples of clusters. 3. The line was also detected in Chandra observations of the Perseus cluster but not in observations of the Virgo cluster. 4. The nature of this line is unclear - it could be a thermal line from an undetected element, or potentially the decay line of a hypothesized dark matter particle called a sterile neutrino. Further observations are needed to determine the origin of the line.
A mildly relativistic wide-angle outflow in the neutron-star merger event GW1...Sérgio Sacani
GW170817 was the first gravitational wave detection of a binary
neutron-star merger1
. It was accompanied by radiation across the
electromagnetic spectrum and localized2
to the galaxy NGC 4993
at a distance of 40 megaparsecs. It has been proposed that the
observed γ-ray, X-ray and radio emission is due to an ultrarelativistic
jet launched during the merger, directed away from
our line of sight3–6. The presence of such a jet is predicted from
models that posit neutron-star mergers as the central engines
that drive short hard γ-ray bursts7,8
. Here we report that the radio
light curve of GW170817 has no direct signature of an off-axis
jet afterglow. Although we cannot rule out the existence of a jet
pointing elsewhere, the observed γ-rays could not have originated
from such a jet. Instead, the radio data require a mildly relativistic
wide-angle outflow moving towards us. This outflow could be the
high-velocity tail of the neutron-rich material dynamically ejected
during the merger or a cocoon of material that breaks out when a
jet transfers its energy to the dynamical ejecta. The cocoon model
explains the radio light curve of GW170817 as well as the γ-rays
and X-rays (possibly also ultraviolet and optical emission)9–15, and
is therefore the model most consistent with the observational data.
Cocoons may be a ubiquitous phenomenon produced in neutronstar
mergers, giving rise to a heretofore unidentified population of
radio, ultraviolet, X-ray and γ-ray transients in the local Universe
The canarias einstein_ring_a_newly_discovered_optical_einstein_ringSérgio Sacani
This document reports the discovery of a newly discovered optical Einstein ring (ER) called the "Canarias Einstein Ring". It was discovered serendipitously in imaging data from the Dark Energy Camera. Follow-up spectroscopy with the Gran Telescopio CANARIAS confirmed the nature of the system, with the lens being an early-type galaxy at a redshift of z=0.581 and the source being a starburst galaxy at z=1.165. Analysis of the system determined the Einstein radius to be 2.16 arcseconds and the total enclosed mass producing the lensing effect to be 1.86 ± 0.23 × 1012 solar masses.
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 .
Detection of an_unidentified_emission_line_in_the_stacked_xray_spectrum_of_ga...Sérgio Sacani
This document describes the detection of an unidentified emission line in the stacked X-ray spectrum of 73 galaxy clusters observed by XMM-Newton. The line was detected at an energy of 3.55-3.57 keV in independent analyses of the MOS and PN instruments. The line was also seen in Chandra observations of the Perseus cluster. Possible explanations discussed include an atomic transition in thermal plasma, or the decay of sterile neutrino dark matter particles. However, the origin is unclear and requires further observation.
Detection of an_unidentified_emission_line_in_the_stacked_xray_spectrum_of_ga...GOASA
This document describes the detection of an unidentified emission line in the stacked X-ray spectrum of 73 galaxy clusters observed by XMM-Newton. The line was detected at an energy of 3.55-3.57 keV in the combined spectrum. It was also seen independently in subsets of the clusters. The line is very weak, with an equivalent width of about 1 eV, and is within 50-110 eV of several known faint lines, making its nature difficult to determine. Possible explanations discussed include an atomic transition in the thermal plasma of the clusters or the decay of sterile neutrino dark matter particles.
The nustar extragalactic_survey_a_first_sensitive_lookSérgio Sacani
The document summarizes the first ten sources detected by the Nuclear Spectroscopic Telescope Array (NuSTAR) as part of its extragalactic survey. NuSTAR provides the first sensitive census of the cosmic X-ray background source population at energies above 10 keV. The ten sources have a broad range of redshifts and luminosities, with a median redshift of 0.7 and luminosity of 3×10^44 erg/s. Based on broad-band spectroscopy and SED analysis, the dominant population is quasars with luminosities above 10^44 erg/s, of which around 50% are obscured. However, none are Compton thick and the fraction of Compton thick quasars is constrained to
Resolved imaging confirms a radiation belt around an ultracool dwarfSérgio Sacani
Radiation belts are present in all large-scale Solar System planetary
30 magnetospheres: Earth, Jupiter, Saturn, Uranus, and Neptune1. These persistent
31 equatorial zones of relativistic particles up to tens of MeV in energy can extend farther
32 than 10 times the planet’s radius, emit gradually varying radio emissions2–4 and impact
33 the surface chemistry of close-in moons5. Recent observations demonstrate that very low
34 mass stars and brown dwarfs, collectively known as ultracool dwarfs, can produce planet35
like radio emissions such as periodically bursting aurorae6–8 from large-scale
36 magnetospheric currents9–11. They also exhibit slowly varying quiescent radio
37 emissions7,12,13 hypothesized to trace low-level coronal flaring14,15 despite departing from
38 empirical multi-wavelength flare relationships8,15. Here we present high resolution
39 imaging of the ultracool dwarf LSR J1835+3259 at 8.4 GHz demonstrating that its
40 quiescent radio emission is spatially resolved and traces a double-lobed and axisymmetric
41 structure similar in morphology to the Jovian radiation belts. Up to 18 ultracool dwarf
42 radii separate the two lobes, which are stably present in three observations spanning
43 more than one year. For plasma confined by the magnetic dipole of LSR J1835+3259, we
44 estimate 15 MeV electron energies consistent with Jupiter’s radiation belts4. Our results
45 confirm recent predictions of radiation belts at both ends of the stellar mass sequence8,16–
46 19 and support broader re-examination of rotating magnetic dipoles in producing non47
thermal quiescent radio emissions from brown dwarfs7, fully convective M dwarfs20, and
4
Spectroscopic confirmation of an ultra-faint galaxy at the epoch of reionizationSérgio Sacani
Within one billion years of the Big Bang, intergalactic hydrogen
was ionized by sources emitting ultraviolet and higher energy
photons. This was the final phenomenon to globally affect all
the baryons (visible matter) in the Universe. It is referred to
as cosmic reionization and is an integral component of cosmology.
It is broadly expected that intrinsically faint galaxies
were the primary ionizing sources due to their abundance
in this epoch1,2. However, at the highest redshifts (z > 7.5;
lookback time 13.1 Gyr), all galaxies with spectroscopic confirmations
to date are intrinsically bright and, therefore, not
necessarily representative of the general population3. Here,
we report the unequivocal spectroscopic detection of a low
luminosity galaxy at z > 7.5. We detected the Lyman-α emission
line at ∼10,504 Å in two separate observations with
MOSFIRE4 on the Keck I Telescope and independently with
the Hubble Space Telescope’s slitless grism spectrograph,
implying a source redshift of z = 7.640 ± 0.001. The galaxy
is gravitationally magnified by the massive galaxy cluster
MACS J1423.8+2404 (z = 0.545), with an estimated intrinsic
luminosity of MAB = −19.6 ± 0.2 mag and a stellar mass of
☆ = × − +
M 3.0 0.8 10
1.5 8 solar masses. Both are an order of magnitude
lower than the four other Lyman-α emitters currently
known at z > 7.5, making it probably the most distant representative
source of reionization found to date.
Radio continum emission_of_35_edge_on_galaxies_observed_with_the_vlaSérgio Sacani
Usando um dos maiores rádio observatórios do mundo, o Very Large Array do National Radio Astronomy, um grupo de astrônomos descobriram que os halos ao redor dos discos das galáxias espirais são muito mais comuns do que se pensava anteriormente.
A equipe, dirigida pela Dra. Judith Irwin, da Universidade de Queens, em Kingston, ON, Canadá, observou 35 galáxias espirais próximas de lado, de 11 a 137 milhões de anos-luz de distância da Terra.
As galáxias espirais, como a nossa própria Via Láctea ou a famosa Galáxia de Andrômeda, possuem uma vasta maioria de suas estrelas, gás, e poeira num disco plano em rotação com braços espirais. A maior parte da luz e das ondas de rádio observadas com telescópios veem de objetos localizados nesse disco.
“Nós sabíamos antes que alguns halos existiam, mas, usando o poder total do VLA atualizado e o poder total de algumas técnicas de processamento de imagens, nós descobrimos que esses halos são muito mais comuns entre as galáxias espirais do que nós pensávamos antes”, explicou a Dra. Irwin.
1. This document describes a multiwavelength campaign on the Seyfert 1 galaxy Mrk 509 using five satellites and two ground-based facilities.
2. The campaign aims to study several open questions about active galactic nuclei (AGN), including the location and physics of outflows from AGN, the nature of continuum emission, the geometry and physical state of the X-ray broad emission line region, and the Fe-K line complex.
3. The observations cover more than five decades in frequency, from 2 μm to 200 keV, and include a simultaneous set of deep XMM-Newton and INTEGRAL observations over seven weeks. This allows the authors to disentangle different components and study time variability
An earth sized_planet_with_an_earth_sized_densitySérgio Sacani
1) Researchers observed the exoplanet Kepler-78b using the HARPS-N spectrograph to measure its mass.
2) They measured Kepler-78b's mass to be 1.86 Earth masses, giving it a density similar to Earth, implying a rocky composition of iron and rock.
3) The small size of Kepler-78b makes it the smallest exoplanet yet measured for both mass and radius, establishing that Earth-sized planets can be terrestrial.
A population of red candidate massive galaxies ~600 Myr after the Big BangSérgio Sacani
Galaxies with stellar masses as high as ~ 1011 solar masses have been identified1–3 out to
33 redshifts z ~ 6, approximately one billion years after the Big Bang. It has been difficult to
34 find massive galaxies at even earlier times, as the Balmer break region, which is needed
35 for accurate mass estimates, is redshifted to wavelengths beyond 2.5 μm. Here we make
36 use of the 1-5 μm coverage of the JWST early release observations to search for
37 intrinsically red galaxies in the first ≈ 750 million years of cosmic history. In the survey
38 area, we find six candidate massive galaxies (stellar mass > 1010 solar masses) at 7.4 ≤ z ≤
39 9.1, 500–700 Myr after the Big Bang, including one galaxy with a possible stellar mass of
40 ~1011 solar masses. If verified with spectroscopy, the stellar mass density in massive
41 galaxies would be much higher than anticipated from previous studies based on rest42
frame ultraviolet-selected samples.
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)
The JWST Discovery of the Triply-imaged Type Ia “Supernova H0pe” and Observat...Sérgio Sacani
A Type Ia supernova (SN) at z = 1.78 was discovered in James Webb Space Telescope Near Infrared
Camera imaging of the galaxy cluster PLCK G165.7+67.0 (G165; z = 0.35). The SN is situated 1.5–
2 kpc from its host galaxy Arc 2 and appears in three different locations as a result of gravitational
lensing by G165. These data can yield a value for Hubble’s constant using time delays from this
multiply-imaged SN Ia that we call “SN H0pe.” Over the entire field we identified 21 image multiplicities,
confirmed five of them using Near-Infrared Spectrograph (NIRspec), and constructed a new
lens model that gives a total mass within 600 kpc of (2.6 ± 0.3) × 1014M⊙. The photometry uncovered
a galaxy overdensity at Arc 2’s redshift. NIRSpec confirmed six member galaxies, four of which
surround Arc 2 with relative velocity ≲900 km s−1 and projected physical extent ≲33 kpc. Arc 2
dominates the stellar mass ((5.0±0.1)×1011M⊙), which is a factor of ten higher than other members
of this compact galaxy group. These other group members have specific star formation rates (sSFR)
arXiv:2309.07326v1 [astro-ph.GA] 13 Sep 2023
2 Frye, Pascale, Pierel et al.
of 2–260 Gyr−1 derived from the Hα-line flux corrected for stellar absorption, dust extinction, and slit
losses. Another group centered on the dusty star forming galaxy Arc 1 is at z = 2.24. The total SFR
for the Arc 1 group (≳400M⊙ yr−1) translates to a supernova rate of ∼1 SNe yr−1, suggesting that
regular monitoring of this cluster may yield additional SNe.
This paper analyzes NuSTAR X-ray observations of 9 optically selected type 2 quasars (QSO2s) at z < 0.5 that were candidates for being Compton-thick based on previous observations. Five new NuSTAR observations are reported. Five of the nine QSO2s were detected by NuSTAR in the 8-24 keV band, with three having sufficient counts for spectral modeling. For these three sources, NuSTAR data found their column densities were 2.5-1600 times higher and intrinsic luminosities were 10-70 times higher than previous estimates from Chandra and XMM-Newton alone. Accounting for these corrections, the authors estimate the Compton-thick fraction of optically selected type
A precise measurement of the magnetic field in the corona of the black hole b...Sérgio Sacani
Observations of binary stars containing an accreting black hole or neutron star often show
x-ray emission extending to high energies (>10 kilo–electron volts), which is ascribed to
an accretion disk corona of energetic particles akin to those seen in the solar corona.
Despite their ubiquity, the physical conditions in accretion disk coronae remain poorly
constrained. Using simultaneous infrared, optical, x-ray, and radio observations of the
Galactic black hole system V404 Cygni, showing a rapid synchrotron cooling event in its
2015 outburst, we present a precise 461 ± 12 gauss magnetic field measurement in the
corona. This measurement is substantially lower than previous estimates for such systems,
providing constraints on physical models of accretion physics in black hole and neutron
star binary systems.
Detectcion of noble_gas_molecular_ion_arh_in_the_crab_nebulaSérgio Sacani
Scientists detected emission lines from the ionized argon hydride (36ArH+) molecule in spectra of the Crab Nebula obtained with the Herschel Space Observatory. The detection of 36ArH+ confirms that argon originated from explosive nucleosynthesis during the core-collapse supernova that created the Crab Nebula. The likely excitation mechanism is electron collisions in partially ionized regions with electron densities of a few hundred per cubic centimeter. This is the first detection of a noble gas molecule in space.
A precise measurement of the magnetic field in the corona of the black hole b...Sérgio Sacani
Observations of binary stars containing an accreting black hole or neutron star often show
x-ray emission extending to high energies (>10 kilo–electron volts), which is ascribed to
an accretion disk corona of energetic particles akin to those seen in the solar corona.
Despite their ubiquity, the physical conditions in accretion disk coronae remain poorly
constrained. Using simultaneous infrared, optical, x-ray, and radio observations of the
Galactic black hole system V404 Cygni, showing a rapid synchrotron cooling event in its
2015 outburst, we present a precise 461 ± 12 gauss magnetic field measurement in the
corona. This measurement is substantially lower than previous estimates for such systems,
providing constraints on physical models of accretion physics in black hole and neutron
star binary systems.
Similar to 44 ti gamma_ray_emission_lines_from_sn1987a_reveal_asymetric_explosion (20)
Evidence of Jet Activity from the Secondary Black Hole in the OJ 287 Binary S...Sérgio Sacani
Wereport the study of a huge optical intraday flare on 2021 November 12 at 2 a.m. UT in the blazar OJ287. In the binary black hole model, it is associated with an impact of the secondary black hole on the accretion disk of the primary. Our multifrequency observing campaign was set up to search for such a signature of the impact based on a prediction made 8 yr earlier. The first I-band results of the flare have already been reported by Kishore et al. (2024). Here we combine these data with our monitoring in the R-band. There is a big change in the R–I spectral index by 1.0 ±0.1 between the normal background and the flare, suggesting a new component of radiation. The polarization variation during the rise of the flare suggests the same. The limits on the source size place it most reasonably in the jet of the secondary BH. We then ask why we have not seen this phenomenon before. We show that OJ287 was never before observed with sufficient sensitivity on the night when the flare should have happened according to the binary model. We also study the probability that this flare is just an oversized example of intraday variability using the Krakow data set of intense monitoring between 2015 and 2023. We find that the occurrence of a flare of this size and rapidity is unlikely. In machine-readable Tables 1 and 2, we give the full orbit-linked historical light curve of OJ287 as well as the dense monitoring sample of Krakow.
Candidate young stellar objects in the S-cluster: Kinematic analysis of a sub...Sérgio Sacani
Context. The observation of several L-band emission sources in the S cluster has led to a rich discussion of their nature. However, a definitive answer to the classification of the dusty objects requires an explanation for the detection of compact Doppler-shifted Brγ emission. The ionized hydrogen in combination with the observation of mid-infrared L-band continuum emission suggests that most of these sources are embedded in a dusty envelope. These embedded sources are part of the S-cluster, and their relationship to the S-stars is still under debate. To date, the question of the origin of these two populations has been vague, although all explanations favor migration processes for the individual cluster members. Aims. This work revisits the S-cluster and its dusty members orbiting the supermassive black hole SgrA* on bound Keplerian orbits from a kinematic perspective. The aim is to explore the Keplerian parameters for patterns that might imply a nonrandom distribution of the sample. Additionally, various analytical aspects are considered to address the nature of the dusty sources. Methods. Based on the photometric analysis, we estimated the individual H−K and K−L colors for the source sample and compared the results to known cluster members. The classification revealed a noticeable contrast between the S-stars and the dusty sources. To fit the flux-density distribution, we utilized the radiative transfer code HYPERION and implemented a young stellar object Class I model. We obtained the position angle from the Keplerian fit results; additionally, we analyzed the distribution of the inclinations and the longitudes of the ascending node. Results. The colors of the dusty sources suggest a stellar nature consistent with the spectral energy distribution in the near and midinfrared domains. Furthermore, the evaporation timescales of dusty and gaseous clumps in the vicinity of SgrA* are much shorter ( 2yr) than the epochs covered by the observations (≈15yr). In addition to the strong evidence for the stellar classification of the D-sources, we also find a clear disk-like pattern following the arrangements of S-stars proposed in the literature. Furthermore, we find a global intrinsic inclination for all dusty sources of 60 ± 20◦, implying a common formation process. Conclusions. The pattern of the dusty sources manifested in the distribution of the position angles, inclinations, and longitudes of the ascending node strongly suggests two different scenarios: the main-sequence stars and the dusty stellar S-cluster sources share a common formation history or migrated with a similar formation channel in the vicinity of SgrA*. Alternatively, the gravitational influence of SgrA* in combination with a massive perturber, such as a putative intermediate mass black hole in the IRS 13 cluster, forces the dusty objects and S-stars to follow a particular orbital arrangement. Key words. stars: black holes– stars: formation– Galaxy: center– galaxies: star formation
JAMES WEBB STUDY THE MASSIVE BLACK HOLE SEEDSSérgio Sacani
The pathway(s) to seeding the massive black holes (MBHs) that exist at the heart of galaxies in the present and distant Universe remains an unsolved problem. Here we categorise, describe and quantitatively discuss the formation pathways of both light and heavy seeds. We emphasise that the most recent computational models suggest that rather than a bimodal-like mass spectrum between light and heavy seeds with light at one end and heavy at the other that instead a continuum exists. Light seeds being more ubiquitous and the heavier seeds becoming less and less abundant due the rarer environmental conditions required for their formation. We therefore examine the different mechanisms that give rise to different seed mass spectrums. We show how and why the mechanisms that produce the heaviest seeds are also among the rarest events in the Universe and are hence extremely unlikely to be the seeds for the vast majority of the MBH population. We quantify, within the limits of the current large uncertainties in the seeding processes, the expected number densities of the seed mass spectrum. We argue that light seeds must be at least 103 to 105 times more numerous than heavy seeds to explain the MBH population as a whole. Based on our current understanding of the seed population this makes heavy seeds (Mseed > 103 M⊙) a significantly more likely pathway given that heavy seeds have an abundance pattern than is close to and likely in excess of 10−4 compared to light seeds. Finally, we examine the current state-of-the-art in numerical calculations and recent observations and plot a path forward for near-future advances in both domains.
Anti-Universe And Emergent Gravity and the Dark UniverseSérgio Sacani
Recent theoretical progress indicates that spacetime and gravity emerge together from the entanglement structure of an underlying microscopic theory. These ideas are best understood in Anti-de Sitter space, where they rely on the area law for entanglement entropy. The extension to de Sitter space requires taking into account the entropy and temperature associated with the cosmological horizon. Using insights from string theory, black hole physics and quantum information theory we argue that the positive dark energy leads to a thermal volume law contribution to the entropy that overtakes the area law precisely at the cosmological horizon. Due to the competition between area and volume law entanglement the microscopic de Sitter states do not thermalise at sub-Hubble scales: they exhibit memory effects in the form of an entropy displacement caused by matter. The emergent laws of gravity contain an additional ‘dark’ gravitational force describing the ‘elastic’ response due to the entropy displacement. We derive an estimate of the strength of this extra force in terms of the baryonic mass, Newton’s constant and the Hubble acceleration scale a0 = cH0, and provide evidence for the fact that this additional ‘dark gravity force’ explains the observed phenomena in galaxies and clusters currently attributed to dark matter.
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.
The cost of acquiring information by natural selectionCarl Bergstrom
This is a short talk that I gave at the Banff International Research Station workshop on Modeling and Theory in Population Biology. The idea is to try to understand how the burden of natural selection relates to the amount of information that selection puts into the genome.
It's based on the first part of this research paper:
The cost of information acquisition by natural selection
Ryan Seamus McGee, Olivia Kosterlitz, Artem Kaznatcheev, Benjamin Kerr, Carl T. Bergstrom
bioRxiv 2022.07.02.498577; doi: https://doi.org/10.1101/2022.07.02.498577
Describing and Interpreting an Immersive Learning Case with the Immersion Cub...Leonel Morgado
Current descriptions of immersive learning cases are often difficult or impossible to compare. This is due to a myriad of different options on what details to include, which aspects are relevant, and on the descriptive approaches employed. Also, these aspects often combine very specific details with more general guidelines or indicate intents and rationales without clarifying their implementation. In this paper we provide a method to describe immersive learning cases that is structured to enable comparisons, yet flexible enough to allow researchers and practitioners to decide which aspects to include. This method leverages a taxonomy that classifies educational aspects at three levels (uses, practices, and strategies) and then utilizes two frameworks, the Immersive Learning Brain and the Immersion Cube, to enable a structured description and interpretation of immersive learning cases. The method is then demonstrated on a published immersive learning case on training for wind turbine maintenance using virtual reality. Applying the method results in a structured artifact, the Immersive Learning Case Sheet, that tags the case with its proximal uses, practices, and strategies, and refines the free text case description to ensure that matching details are included. This contribution is thus a case description method in support of future comparative research of immersive learning cases. We then discuss how the resulting description and interpretation can be leveraged to change immersion learning cases, by enriching them (considering low-effort changes or additions) or innovating (exploring more challenging avenues of transformation). The method holds significant promise to support better-grounded research in immersive learning.
Immersive Learning That Works: Research Grounding and Paths ForwardLeonel Morgado
We will metaverse into the essence of immersive learning, into its three dimensions and conceptual models. This approach encompasses elements from teaching methodologies to social involvement, through organizational concerns and technologies. Challenging the perception of learning as knowledge transfer, we introduce a 'Uses, Practices & Strategies' model operationalized by the 'Immersive Learning Brain' and ‘Immersion Cube’ frameworks. This approach offers a comprehensive guide through the intricacies of immersive educational experiences and spotlighting research frontiers, along the immersion dimensions of system, narrative, and agency. Our discourse extends to stakeholders beyond the academic sphere, addressing the interests of technologists, instructional designers, and policymakers. We span various contexts, from formal education to organizational transformation to the new horizon of an AI-pervasive society. This keynote aims to unite the iLRN community in a collaborative journey towards a future where immersive learning research and practice coalesce, paving the way for innovative educational research and practice landscapes.
Authoring a personal GPT for your research and practice: How we created the Q...Leonel Morgado
Thematic analysis in qualitative research is a time-consuming and systematic task, typically done using teams. Team members must ground their activities on common understandings of the major concepts underlying the thematic analysis, and define criteria for its development. However, conceptual misunderstandings, equivocations, and lack of adherence to criteria are challenges to the quality and speed of this process. Given the distributed and uncertain nature of this process, we wondered if the tasks in thematic analysis could be supported by readily available artificial intelligence chatbots. Our early efforts point to potential benefits: not just saving time in the coding process but better adherence to criteria and grounding, by increasing triangulation between humans and artificial intelligence. This tutorial will provide a description and demonstration of the process we followed, as two academic researchers, to develop a custom ChatGPT to assist with qualitative coding in the thematic data analysis process of immersive learning accounts in a survey of the academic literature: QUAL-E Immersive Learning Thematic Analysis Helper. In the hands-on time, participants will try out QUAL-E and develop their ideas for their own qualitative coding ChatGPT. Participants that have the paid ChatGPT Plus subscription can create a draft of their assistants. The organizers will provide course materials and slide deck that participants will be able to utilize to continue development of their custom GPT. The paid subscription to ChatGPT Plus is not required to participate in this workshop, just for trying out personal GPTs during it.
The technology uses reclaimed CO₂ as the dyeing medium in a closed loop process. When pressurized, CO₂ becomes supercritical (SC-CO₂). In this state CO₂ has a very high solvent power, allowing the dye to dissolve easily.
PPT on Direct Seeded Rice presented at the three-day 'Training and Validation Workshop on Modules of Climate Smart Agriculture (CSA) Technologies in South Asia' workshop on April 22, 2024.
Current Ms word generated power point presentation covers major details about the micronuclei test. It's significance and assays to conduct it. It is used to detect the micronuclei formation inside the cells of nearly every multicellular organism. It's formation takes place during chromosomal sepration at metaphase.
44 ti gamma_ray_emission_lines_from_sn1987a_reveal_asymetric_explosion
1. 670 8 MAY 2015 • VOL 348 ISSUE 6235 sciencemag.org SCIENCE
SUPERNOVAE
44
Ti gamma-ray emission lines
from SN1987A reveal an
asymmetric explosion
S. E. Boggs,1
* F. A. Harrison,2
H. Miyasaka,2
B. W. Grefenstette,2
A. Zoglauer,1
C. L. Fryer,3
S. P. Reynolds,4
D. M. Alexander,5
H. An,6
D. Barret,7,8
F. E. Christensen,9
W. W. Craig,1,10
K. Forster,2
P. Giommi,11
C. J. Hailey,12
A. Hornstrup,9
T. Kitaguchi,13
J. E. Koglin,14
K. K. Madsen,2
P. H. Mao,2
K. Mori,12
M. Perri,11,15
M. J. Pivovaroff,10
S. Puccetti,11,15
V. Rana,2
D. Stern,16
N. J. Westergaard,9
W. W. Zhang17
In core-collapse supernovae, titanium-44 (44
Ti) is produced in the innermost ejecta,
in the layer of material directly on top of the newly formed compact object. As such,
it provides a direct probe of the supernova engine. Observations of supernova 1987A
(SN1987A) have resolved the 67.87- and 78.32–kilo–electron volt emission lines from
decay of 44
Ti produced in the supernova explosion. These lines are narrow and
redshifted with a Doppler velocity of ~700 kilometers per second, direct evidence
of large-scale asymmetry in the explosion.
S
upernova 1987A (SN1987A) in the Large
Magellanic Cloud provides a unique op-
portunity to study a nearby (50 kpc) core
collapse supernova (CCSN) explosion and
its subsequent evolution into a supernova
remnant. SN1987A has validated some of our
most basic assumptions about CCSN. The burst
of neutrinos observed on Earth that preceded the
visible emission confirmed that the overall ex-
plosion is driven by the collapse of the central
core to a neutron star (1, 2). The direct gamma-
ray detections of 0.07 solar mass (M⊙) of 56
Co
(3, 4) and 0.003 M⊙ of 57
Co (5), and the cor-
relation between the exponential decay of the
optical light curve and lifetime of these isotopes
(6, 7), confirmed that the light curve is driven by
radioactive decay of these nuclei.
SN1987A, however, held a few surprises. Models
and light curves supported red supergiant pro-
genitors for CCSN, but the SN1987A progenitor
was blue (8). The 56
Co gamma-ray lines emerged
from the explosion several months before ex-
pected, implying that some of the innermost
heavy nuclear products had been mixed into
the outer envelope (3). The 56
Co gamma-ray
line spectroscopy showed mixing to velocities of
∼3000 km s−1
, several times higher than expected
from spherically symmetric models, and also a
net redshift of ∼500 km s−1
, which indicated
large-scale asymmetry (9, 10). Although subsequent
x-ray observations have revealed expanding,
brightening ejecta, there has been no evidence
of the compact object created in the explosion
(11, 12).
Here we present observations of 44
Ti emission
from SN1987A with the Nuclear Spectroscopic
Telescope Array (NuSTAR) focusing high-energy
x-ray telescope (13). 44
Ti production occurs deep
inside the supernova near the dividing line
between ejecta and material that falls back on
the compact object, and is sensitive to the CCSN
explosion energy and asymmetries (14, 15). The
decay of 44
Ti (85.0 years) results in the produc-
tion of photons at 67.87 keV (93.0% of decays)
and 78.32 keV (96.4% of decays) (16). NuSTAR
observed SN1987A for multiple epochs between
September 2012 and July 2014 with a total ex-
posure of 2596 ks, at an average time of ~26.6
years after explosion. A full list of the observa-
tions is provided in table S1. Both the 67.87-keV
line and the 78.32-keV lines of 44
Ti are clearly
seen in the NuSTAR spectrum (Fig. 1). The lines
are well fit with a simple Gaussian line shape
plus the underlying continuum, demonstrated
through the chi-square test. All uncertainties
are quoted here at the 90% confidence level
unless otherwise stated. In the combined anal-
ysis, we measure a 67.87-keV line flux of 3:5þ0:7
−0:7 Â
10−6
photons cm−2
s−1
, corresponding to a 44
Ti
yield of 1:5þ0:3
−0:3 Â 10−4
M⊙. This derived yield
assumes the decay rate measured in the lab-
oratory and nearly neutral 44
Ti. The NuSTAR
optics response cuts off at 78.39 keV, poten-
tially cutting off any blueshifted emission. How-
ever, examination of the 67.87-keV line reveals
a net redshift, allowing us to combine the lines
for optimal analysis and use the individual lines
to check for consistency (17). The signal-to-noise
ratio for the detection of these combined lines
is ∼8.5s. The line widths are consistent with
the NuSTAR spectral resolution, and the corre-
sponding upper limit on any Doppler broad-
ening is 4100 km s−1
full width at half-maximum
(FWHM). The 67.87-keV line centroid is red-
shifted by 0:23þ0:09
−0:09 keV. Corrections due to
recession velocity and the look-back effect (17)
are ≤ 340 km s−1
combined. Taking these cor-
rections into account, the redshift velocity of
the 44
Ti lines in the rest frame of SN1987A is
700þ400
−400 km s−1
.
The NuSTAR yield can be compared to pre-
vious measurements, indirect estimates, and theo-
retical predictions. The International Gamma Ray
Astrophysics Laboratory (INTEGRAL) observa-
tory reported first detection of the 44
Ti 67.87-keV
and78.32-keV lines fromSN1987A(18). INTEGRAL
could not spectrally resolve these lines, but mea-
sured a combined flux for both lines of (1.7 T 0.4) ×
10−5
photons cm−2
s−1
, corresponding to an initial
mass of synthesized 44
Ti of (3.1 T 0.8) × 10−4
M⊙.
The yield measured by NuSTAR is inconsistent
with the high yield found by INTEGRAL. Chandra
X-ray Observatory Advanced CCD Imaging Spec-
trometer (ACIS) limits on Sc Ka emission have
been used to set an upper limit on the 44
Ti mass
of <2 × 10−4
M⊙ (19), consistent with the NuSTAR
yield. Between 1994 and 2001, the ultraviolet,
optical, and infrared (UVOIR) emission was dom-
inated by the radioactive decay of 44
Ti, which led
to a number of estimates of the 44
Ti yield based on
detailed modeling of the UVOIR spectra (20–22)
and bolometric luminosity (23, 24). These obser-
vational studies do not all agree within their
uncertainties, but generally fall in the range of (0.5
to 2) × 10−4
M⊙ of 44
Ti produced in the explosion
(24). The 44
Ti yield measured by NuSTAR is in
good agreement with most estimates based on the
UVOIR bolometric light curves and spectroscopic
modeling, providing support for the detailed
models underlying these estimates; however, our
measured redshift reveals a more complicated
explosion structure than assumed in these models.
Finally, theoretical predictions of the 44
Ti yield
for SN1987A fall roughly within this same range
of (0.5 to 2) × 10−4
M⊙, with lower yields gen-
erally corresponding to spherically symmetric mod-
els, and yields increasing with larger asymmetries.
See reference (24) for a compilation of theory
references.
NuSTAR observations have set an upper limit
on the Doppler broadening of <4100 km s−1
FWHM, consistent with the widths of ∼3000 km s−1
1
Space Sciences Laboratory, University of California,
Berkeley, CA 94720, USA. 2
Cahill Center for Astronomy and
Astrophysics, California Institute of Technology, Pasadena,
CA 91125, USA. 3
CCS-2, Los Alamos National Laboratory, Los
Alamos, NM 87545, USA. 4
Physics Department, NC State
University, Raleigh, NC 27695, USA. 5
Department of Physics,
Durham University, Durham DH1 3LE, UK. 6
Department of
Physics, McGill University, Rutherford Physics Building,
Montreal, Quebec H3A 2T8, Canada. 7
Université de Toulouse,
UPS-OMP, IRAP, Toulouse, France. 8
CNRS, Institut de
Recherche en Astrophysique et Planétologie, 9 Av. colonel
Roche, BP 44346, F-31028 Toulouse Cedex 4, France. 9
DTU
Space, National Space Institute, Technical University of
Denmark, Elektrovej 327, DK-2800 Lyngby, Denmark.
10
Lawrence Livermore National Laboratory, Livermore, CA
94550, USA. 11
Agenzia Spaziale Italiana (ASI) Science Data
Center, Via del Politecnico snc I-00133, Roma, Italy.
12
Columbia Astrophysics Laboratory, Columbia University,
New York, NY 10027, USA. 13
RIKEN Nishina Center, 2-1
Hirosawa, Wako, Saitama, 351-0198, Japan. 14
Kavli Institute
for Particle Astrophysics and Cosmology, SLAC National
Accelerator Laboratory, Menlo Park, CA 94025, USA.
15
INAF – Osservatorio Astronomico di Roma, via di Frascati
33, I-00040 Monteporzio, Italy. 16
Jet Propulsion Laboratory,
California Institute of Technology, Pasadena, CA 91109, USA.
17
NASA Goddard Space Flight Center, Greenbelt,
MD 20771, USA.
*Corresponding author. E-mail: boggs@berkeley.edu
RESEARCH | REPORTS
onMay11,2015www.sciencemag.orgDownloadedfromonMay11,2015www.sciencemag.orgDownloadedfrom
2. originally measured for the 56
Co lines (9, 10).
Although the limit on broadening itself is not
surprising, the measured redshift is both statis-
tically significant and large compared to the up-
per limit on Doppler broadening, indicative of
an asymmetric ejection of 44
Ti in the initial ex-
plosion. The 56
Co gamma-ray lines also showed
redshifts (∼500 km s−1
), but the significance was
marginal. The 56
Co detection also stands con-
trary to predictions of spherically symmetric
explosion models that would produce blue-
shifted gamma-ray lines due to increased absorp-
tion of the receding redshifted emission. The
redshifted 56
Co lines suggest large-scale asym-
metry in the explosion.
There has been growing evidence for asym-
metries in supernovae explosions over the past
decades (25). In SN1987A itself, asymmetry was
initially supported by extensive evidence for
mixing and polarized optical emission as re-
viewed in (26, 27), and later by spatially resolved
images of the ejecta (27, 28). NuSTAR observa-
tions of the spatial distribution of 44
Ti in the Cas
A supernova remnant shows direct evidence of
asymmetry (29). Our results here suggest an even
higher level of asymmetry for SN1987A. For com-
parison, NuSTAR measured a redshift for the in-
tegrated Cas A spectrum of (2100 T 900) km s−1
and a line broadening corresponding to a fastest
ejection velocity of ∼5000 km s−1
. Given that ejec-
tionvelocityandtheageof theremnant(340years),
the estimated “look-back” redshift velocity for
Cas A is ∼1400 km s−1
, consistent with the mea-
sured redshift. From the spatially integrated 44
Ti
spectrum alone, Cas A would not appear to have
a statistically significant asymmetry: The spatial
brightness distribution in Cas A revealed the
asymmetries.
In the 44
Ti-powered phase, the dominant en-
ergy input to the ejecta comes through the sub-
sequent positron emission of 44
Sc, when most
of the gamma rays escape the ejecta without
interacting. These positrons are produced deep
in the ejecta, and both simple estimates and de-
tailed models suggest that they are locally ab-
sorbed and instantaneously thermalized (20, 22).
The implication is that the UVOIR emission of
SN1987A during the 44
Ti-powered phase should
be dominated by the ejecta spatially coinci-
dent with the 44
Ti ejecta. In principle, UVOIR
spectral imaging in the 44
Ti-powered phase
can yield direct evidence for asymmetries. Hub-
ble Space Telescope (HST) obtained resolved
spectral images of the SN1987A ejecta (28)
from June 2000 (4857 days after explosion), near
the end of the phase when the UVOIR emis-
sion was truly dominated by 44
Ti decay (21).
They reveal a bipolar structure elongated along
the north-south direction. There is a clear gra-
dient in velocity across ejecta, with the north-
ern component showing a redshift of about
500 km s−1
in the [Ca II] l7300 emission line,
whereas the southern component showed a
larger redshift of about 1700 km s−1
. The ejecta
exhibit an overall redshift of ~1000 km s−1
. At
the time, this asymmetry and overall redshift
were noted but not emphasized, as they could
be the result of blending of the [Ca II] l7300
line with a [O II] l7320 line. This shifted vel-
ocity distribution is consistent with our mea-
sured redshift of the 44
Ti lines. On the basis of
our 44
Ti line profile, we might naïvely imagine
the picture of a bright, redshifted clump or jet
of 44
Ti, with the UVOIR emission tracing the
spatial and velocity distribution of this clump.
However, the spatial distribution of the ejecta
in this HST observation does not immediately
reveal such a large spatial asymmetry.
A single-lobe (i.e., very asymmetric) explosion
model for SN1987A (30) could explain the ob-
served evidence that 56
Ni was mixed to speeds
exceeding 3000 km s−1
and redshifted, as evi-
denced by both the gamma-ray emission and the
infrared forbidden line profiles of [Fe II] (mainly
produced through 56
Ni decay) around 400 days
after the explosion (31, 32). In this model, the
single lobe is oriented at an angle pointing away
from us, producing the redshifted lines (30). The
NuSTARobservationsappearconsistentwiththese
single-lobe models. One consequence of such a
highly asymmetric explosion is that the compact
object produced by SN1987A would, presumably,
receive a kick velocity opposite the direction of
the ejecta (33).
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ACKNOWLEDGMENTS
This work was supported under NASA Contract no. NNG08FD60C
and made use of data from the NuSTAR mission, a project led by
the California Institute of Technology, managed by the Jet
Propulsion Laboratory, and funded by the National Aeronautics
and Space Administration. We thank the NuSTAR Operations,
Software, and Calibration teams for support with the execution
and analysis of these observations. This research has made use of
the NuSTAR Data Analysis Software (NuSTARDAS) jointly
developed by the ASI Science Data Center (ASDC, Italy) and the
California Institute of Technology (USA). D.B. acknowledges
funding from the French Space Agency (CNES). T.K. was
supported by Japan Society for the Promotion of Science
Grant-in-Aid for Young Scientists (B) (no. 24740185). N.J.W.
acknowledges funding from the Technical University of Denmark.
NuSTAR data are accessible from NASA’s High Energy
Astrophysics Science Archive Research Center (HEASARC,
http://heasarc.gsfc.nasa.gov/).
SUPPLEMENTARY MATERIALS
www.sciencemag.org/content/348/6235/670/suppl/DC1
Materials and Methods
Figs. S1 to S3
Tables S1 and S2
References (34–36)
3 November 2014; accepted 8 April 2015
10.1126/science.aaa2259
SCIENCE sciencemag.org 8 MAY 2015 • VOL 348 ISSUE 6235 671
Fig. 1. SN1987A 55- to 80-keV
background-subtracted spectrum
measured with NuSTAR. Data from
both telescopes are combined (for
presentation only) and shown with
1s error bars. Both of the 44
Ti lines are
clearly measured. The vertical green
lines are the rest-frame energies of the
44
Ti lines (67.87 and 78.32 keV). The
redshift is evident in both lines, indi-
cating the asymmetry of the explosion.
Also shown is the best-fit model, con-
volved through the NuSTAR instrument
response, for case (1), where the fitting
parameters for the two lines are tied
together (supplementary materials).
Ctssec-1
keV-1
Energy (keV)
Rest Frame
RESEARCH | REPORTS
3. DOI: 10.1126/science.aaa2259
, 670 (2015);348Science
et al.S. E. Boggs
explosion
Ti gamma-ray emission lines from SN1987A reveal an asymmetric44
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