21 research outputs found
The Galactic Centre source G2 was unlikely born in any of the known massive binaries
The source G2 has already completed its pericentre passage around Sgr A*, the
super-massive black hole in the centre of our Galaxy. Although it has been
monitored for 15 years, its astrophysical nature and origin still remain
unknown. In this work, we aim to test the hypothesis of G2 being the result of
a stellar wind collision. To do so, we study the motion and final fate of gas
clumps formed as a result of collisions of stellar winds in massive binaries.
Our approach is based on a test-particle model in order to describe the
trajectories of such clumps. The model takes into account the gravitational
field of Sgr A*, the interaction of the clumps with the interstellar medium as
well as their finite lifetimes. Our analysis allows us to reject the hypothesis
based on four arguments: i) if G2 has followed a purely Keplerian orbit since
its formation, it cannot have been produced in any of the known massive
binaries since their motions are not consistent; ii) in general, gas clumps are
evaporated through thermal conduction on very short timescale (< 100yr) before
getting close enough to Sgr A*; iii) IRS 16SW, the best candidate for the
origin of G2, cannot generate clumps as massive as G2; and iv) clumps ejected
from IRS 16SW describe trajectories significantly different to the observed
motion of G2.Comment: 14 pages, 10 figures. Accepted for publication in MNRA
ReStainGAN: Leveraging IHC to IF Stain Domain Translation for in-silico Data Generation
The creation of in-silico datasets can expand the utility of existing
annotations to new domains with different staining patterns in computational
pathology. As such, it has the potential to significantly lower the cost
associated with building large and pixel precise datasets needed to train
supervised deep learning models. We propose a novel approach for the generation
of in-silico immunohistochemistry (IHC) images by disentangling morphology
specific IHC stains into separate image channels in immunofluorescence (IF)
images. The proposed approach qualitatively and quantitatively outperforms
baseline methods as proven by training nucleus segmentation models on the
created in-silico datasets.Comment: 4 pages, 1 figur
A Detection of Sgr A* in the far infrared
We report the first detection of the Galactic Centre massive black hole,
Sgr~A*, in the far infrared. Our measurements were obtained with PACS on board
the \emph{Herschel} satellite at and .
While the warm dust in the Galactic Centre is too bright to allow for a direct
detection of Sgr~A*, we measure a significant and simultaneous variation of its
flux of and during one observation. The significance level of
the band variability is and the corresponding
band variability is significant at . We find
no example of an equally significant false positive detection. Conservatively
assuming a variability of in the FIR, we can provide upper limits to the
flux. Comparing the latter with theoretical models we find that 1D RIAF models
have difficulties explaining the observed faintness. However, the upper limits
are consistent with modern ALMA and VLA observations. Our upper limits provide
further evidence for a spectral peak at and
constrain the number density of electrons in the accretion
disk and or outflow.Comment: accepted for publication in AP
Testing General Relativity with the Shadow Size of Sgr
In general relativity, the angular radius of the shadow of a black hole is primarily determined by its mass-to-distance ratio and depends only weakly on its spin and inclination. If general relativity is violated, however, the shadow size may also depend strongly on parametric deviations from the Kerr metric. Based on a reconstructed image of Sagittarius A∗ (Sgr A∗) from a simulated one-day observing run of a seven-station Event Horizon Telescope (EHT) array, we employ a Markov chain Monte Carlo algorithm to demonstrate that such an observation can measure the angular radius of the shadow of Sgr A∗ with an uncertainty of ∼1.5 μas (6%). We show that existing mass and distance measurements can be improved significantly when combined with upcoming EHT measurements of the shadow size and that tight constraints on potential deviations from the Kerr metric can be obtained.Gordon and Betty Moore Foundation (Grant GBMF-3561
Catching Element Formation In The Act
Gamma-ray astronomy explores the most energetic photons in nature to address
some of the most pressing puzzles in contemporary astrophysics. It encompasses
a wide range of objects and phenomena: stars, supernovae, novae, neutron stars,
stellar-mass black holes, nucleosynthesis, the interstellar medium, cosmic rays
and relativistic-particle acceleration, and the evolution of galaxies. MeV
gamma-rays provide a unique probe of nuclear processes in astronomy, directly
measuring radioactive decay, nuclear de-excitation, and positron annihilation.
The substantial information carried by gamma-ray photons allows us to see
deeper into these objects, the bulk of the power is often emitted at gamma-ray
energies, and radioactivity provides a natural physical clock that adds unique
information. New science will be driven by time-domain population studies at
gamma-ray energies. This science is enabled by next-generation gamma-ray
instruments with one to two orders of magnitude better sensitivity, larger sky
coverage, and faster cadence than all previous gamma-ray instruments. This
transformative capability permits: (a) the accurate identification of the
gamma-ray emitting objects and correlations with observations taken at other
wavelengths and with other messengers; (b) construction of new gamma-ray maps
of the Milky Way and other nearby galaxies where extended regions are
distinguished from point sources; and (c) considerable serendipitous science of
scarce events -- nearby neutron star mergers, for example. Advances in
technology push the performance of new gamma-ray instruments to address a wide
set of astrophysical questions.Comment: 14 pages including 3 figure
Multiple star systems in the Orion nebula
This is the author accepted manuscript. The final fersion is available from EDP Sciences via the DOI in this record.This work presents an interferometric study of the massive-binary fraction in the Orion Trapezium cluster with the recently comissioned GRAVITY instrument. We observed a total of 16 stars of mainly OB spectral type. We find three previously unknown companions for θ1 Ori B, θ2 Ori B, and θ2 Ori C. We determined a separation for the previously suspected companion of NU Ori. We confirm four companions for θ1 Ori A, θ1 Ori C, θ1 Ori D, and θ2 Ori A, all with substantially improved astrometry and photometric mass estimates. We refined the orbit of the eccentric high-mass binary θ1 Ori C and we are able to derive a new orbit for θ1 Ori D. We find a system mass of 21.7 M⊙ and a period of 53 days. Together with other previously detected companions seen in spectroscopy or direct imaging, eleven of the 16 high-mass stars are multiple systems. We obtain a total number of 22 companions with separations up to 600 AU. The companion fraction of the early B and O stars in our sample is about two, significantly higher than in earlier studies of mostly OB associations. The separation distribution hints toward a bimodality. Such a bimodality has been previously found in A stars, but rarely in OB binaries, which up to this point have been assumed to be mostly compact with a tail of wider companions. We also do not find a substantial population of equal-mass binaries. The observed distribution of mass ratios declines steeply with mass, and like the direct star counts, indicates that our companions follow a standard power law initial mass function. Again, this is in contrast to earlier findings of flat mass ratio distributions in OB associations. We excluded collision as a dominant formation mechanism but find no clear preference for core accretion or competitive accretion.Marie Skłodowska-Curie Grant AgreementFCT-PortugalERC Starting Gran