* Astronomy

Members Login
Post Info TOPIC: Galactic Center


L

Posts: 131433
Date:
RE: Galactic Center
Permalink  
 


ATel 10089: Swift resumes X-ray monitoring observations of the Galactic center in 2017



__________________


L

Posts: 131433
Date:
Permalink  
 

Title: Can flaring stars explain the annihilation line from the Galaxy bulge?
Author: G.S. Bisnovatyi-Kogan, A.S. Pozanenko

Electron-positron annihilation line from a Galactic center direction was discovered by the balloon-borne germanium gamma-ray telescope, and confirmed by OSSE experiment of CGRO mission. Extensive observations by INTEGRAL observatory permit to determine properties of the annihilation line from Galactic bulge. Possible sources of e+ already discussed are supernovae explosions, microquasars, gamma-ray bursts, tidal disruption events, activity near black hole of Sgr A*, e+ generation by subrelativistic cosmic rays, or even dark matter. One remarkable feature of the line emission is an absence of resolved point like sources. Any model should take into account this feature. We consider flares of low-mass stars as a possible cumulative e+ source of the observed annihilation line from the bulge. Our estimations show that e+ production by numerous flaring stars in Galaxy bulge can be significant, or even the main source of e+ responsible for the annihilation line observed from the central part of our Galaxy.

Read more (7kb, PDF)



__________________


L

Posts: 131433
Date:
Permalink  
 

Title: Discovery of Gamma-Ray Emission from the X-shaped Bulge of the Milky Way
Author: Oscar Macias, Chris Gordon, Roland M. Crocker, Brendan Coleman, Dylan Paterson, Shunsaku Horiuchi, Martin Pohl

n anomalous signal has been found in Fermi Gamma-Ray Large Area Telescope data covering the center of the Galaxy. Given its morphological and spectral characteristics, this "Galactic Center Excess" is ascribable to self-annihilation of dark matter particles. We report on an analysis that exploits hydrodynamical modelling to register the position of interstellar gas associated with diffuse Galactic gamma-ray emission. Our improved analysis reveals that the excess gamma-rays are spatially correlated with both the X-shaped stellar over-density in the Galactic bulge and the nuclear stellar bulge. Given these correlations, we argue that the excess is not a dark matter phenomenon but rather associated with the stellar population of the X-bulge and the nuclear bulge.

Read more (7108kb, PDF)



__________________


L

Posts: 131433
Date:
Permalink  
 

The Milky Way's Ancient Heart

Ancient stars, of a type known as RR Lyrae, have been discovered in the centre of the Milky Way for the first time, using ESO's infrared VISTA telescope. RR Lyrae stars typically reside in ancient stellar populations over 10 billion years old. Their discovery suggests that the bulging centre of the Milky Way likely grew through the merging of primordial star clusters. These stars may even be the remains of the most massive and oldest surviving star cluster of the entire Milky Way.
A team led by Dante Minniti (Universidad Andrés Bello, Santiago, Chile) and Rodrigo Contreras Ramos (Instituto Milenio de Astrofísica, Santiago, Chile) used observations from the VISTA infrared survey telescope, as part of the Variables in the Via Lactea (VVV) ESO public survey, to carefully search the central part of the Milky Way. By observing infrared light, which is less affected by cosmic dust than visible light, and exploiting the excellent conditions at ESO-s Paranal Observatory, the team was able to get a clearer view of this region than ever before. They found a dozen ancient RR Lyrae stars at the heart of the Milky Way that were previously unknown.

Read more



__________________


L

Posts: 131433
Date:
Permalink  
 

Radio Telescopes Could Spot Stars Hidden in the Galactic Center

The center of our Milky Way galaxy is a mysterious place. Not only is it thousands of light-years away, it's also cloaked in so much dust that most stars within are rendered invisible. Harvard researchers are proposing a new way to clear the fog and spot stars hiding there. They suggest looking for radio waves coming from supersonic stars.
Read more



__________________


L

Posts: 131433
Date:
RE: Galactic Center Cluster
Permalink  
 


Title: Mapping the Outer Edge of the Young Stellar Cluster in the Galactic Center
Author: Morten N. Støstad, Tuan Do, Norm Murray, Jessica R. Lu, Sylvana Yelda, Andrea M. Ghez

We present new near-infrared spectroscopic observations of the outer edges of the young stellar cluster around the supermassive black hole at the Galactic center. The observations show a break in the surface-density profile of young stars at approximately 13 arcsec (0.52 pc). These observations spectroscopically confirm previous suggestions of a break based on photometry. Using Gemini North's Near-Infrared Integral Field Spectrometer (NIFS) we are able to detect and separate early- and late-type stars with a 75% completeness at Ks = 15.5. We sample a region with radii between 7" to 23" (0.28 pc to 0.92 pc) from Sgr A*, and present new spectral classifications of 144 stars brighter than Ks = 15.5, where 140 stars are late-type (> 1 Gyr) and only four stars are early-type (young, 4-6 Myr). A broken power-law fit of the early-type surface-density matches well with our data and previously published values. The projected surface-density of late-type stars is also measured and found to be consistent with previous results. We find that the observed early-type surface-density profile is inconsistent with the theory of the young stars originating from a tightly bound infalling cluster, as no significant trail of young stars is found at radii above 13". We also note that either a simple disk instability criterion or a cloud-cloud collision could explain the location of the outer edge, though we lack information to make conclusive remarks on either alternative. If this break in surface-density represents an edge to the young stellar cluster it would set an important scale for the most recent episode of star formation at the Galactic center.

Read more (647kb, PDF)



__________________


L

Posts: 131433
Date:
RE: Galactic Center
Permalink  
 


Title: On the origin of the B-stars in the Galactic center
Authors: Ann-Marie Madigan, Yuri Levin, Oliver Pfuhl, Reinhard Genzel, Hagai B. Perets

We present a new directly-observable statistic which uses sky position and proper motion of stars near the Galactic center massive black hole to identify populations with high orbital eccentricities. It is most useful for stars with large orbital periods for which dynamical accelerations are difficult to determine. We apply this statistic to a data set of B-stars with projected radii 0."1 < p < 25" (~0.004 - 1 pc) from the massive black hole in the Galactic center. We compare the results with those from N-body simulations to distinguish between scenarios for their formation. We find that the scenarios favored by the data correlate strongly with particular K-magnitude intervals, corresponding to different zero-age main-sequence (MS) masses and lifetimes. Stars with 14 < mK < 15 (15 - 20 solar masses, t_{MS} = 8-13 Myr) match well to a disk formation origin, while those with mK > 15 (<15 solar masses, t_{MS} >13 Myr), if isotropically distributed, form a population that is more eccentric than thermal, which suggests a Hills binary-disruption origin.

Read more (570kb, PDF)



__________________


L

Posts: 131433
Date:
Permalink  
 

Galactic geysers fuelled by star stuff

Enormous outflows of charged particles from the centre of our Galaxy, stretching more than halfway across the sky and moving at supersonic speeds, have been detected and mapped with CSIRO's 64-m Parkes radio telescope.
Corresponding to the "Fermi Bubbles" found in 2010, the recent observations of the phenomenon were made by a team of astronomers from Australia, the USA, Italy and The Netherlands, with the findings reported in today's issue of Nature.

Read more



__________________


L

Posts: 131433
Date:
Permalink  
 

Title: A 130 GeV Gamma Ray Signal from Supersymmetry
Authors: Bibhushan Shakya

The viability of neutralino dark matter as an explanation of the 130 GeV gamma ray signal from the Galactic Center recently observed by the Fermi Large Area Telescope is examined. It is found that the signal can be compatible with a sharp feature from internal bremsstrahlung from a mostly bino dark matter particle of mass around 145 GeV, augmented by a contribution from annihilation into gamma+Z via a small wino admixture. This scenario circumvents the problematic overproduction of lower energy continuum photons that plague line interpretations of this signal. Sleptons approximately degenerate in mass with the neutralino are required to enhance the internal bremsstrahlung feature.

Read more (690kb, PDF)

Ed ~ See previous post



__________________


L

Posts: 131433
Date:
Galactic Haze
Permalink  
 


Dark-matter hope fades in microwave haze

The latest results from the Planck space telescope have confirmed the presence of a microwave haze at the centre of the Milky Way. However, the haze appears to be more elongated than originally thought, which casts doubt over previous claims that annihilating dark matter is the cause of the emissions.
Read more



__________________
1 2  >  Last»  | Page of 2  sorted by
Quick Reply

Please log in to post quick replies.



Create your own FREE Forum
Report Abuse
Powered by ActiveBoard