scholarly journals The central cluster and X-ray emission from Sgr A*

2006 ◽  
Vol 2 (S238) ◽  
pp. 347-348
Author(s):  
Robert F. Coker ◽  
Julian M. Pittard
Keyword(s):  
Black Hole ◽  
Stellar Winds ◽  
Solar Mass ◽  
Hydrodynamic Simulations ◽  
X Ray ◽  
Central Cluster ◽  
The Galaxy ◽  
Early Type Stars ◽  
Sgr A ◽  
Hydrodynamic Data

AbstractAt the centre of the Milky Way is Sgr A*, a putative 3 million solar mass black hole with an observed luminosity that is orders of magnitude smaller than that expected from simple accretion theories. The number density of early-type stars is quite high near Sgr A*, so the ensemble of their stellar winds has a significant impact on the black hole's environment.We present results of 3D hydrodynamic simulations of the accretion of stellar winds onto Sgr A*. Using the LANL/SAIC code, RAGE, we model the central arc-second of the Galaxy, including the central cluster stars (the S-stars) with orbits and wind parameters that match observations. A significant fraction of the winds from the S stars becomes gravitationally bound to the black hole and thus could provide enough hot gas to produce the X-ray emission seen by Chandra. We perform radiative transfer calculations on the 3D hydrodynamic data cubes and present the resulting synthetic X-ray spectrum.

scholarly journals Galactic Center: Implications of Recent Chandra Observations for Spherical Accretion Models of Sgr A*

2001 ◽  
Vol 205 ◽  
pp. 32-35 ◽  
Author(s):  
Robert F. Coker ◽  
Sera Markoff
Keyword(s):  
Galactic Center ◽  
Stellar Winds ◽  
Early Type ◽  
Solar Mass ◽  
X Ray ◽  
Nonthermal Radio ◽  
Accretion Model ◽  
Early Type Stars ◽  
Sgr A ◽  
Central Parsec

At the center of the Milky Way lurks a unique compact nonthermal radio source, Sgr A*. It is thought to be powered by a 2.6 × 106 solar mass black hole that is accreting the stellar winds from the numerous early-type stars that exist in the central parsec. However, until recent high resolution Chandra observations, Sgr A* had never been unequivocably detected at wavelengths shorter than the sub-millimeter. We present a spherical accretion model which is consistent with both the flux and steep spectral shape of the X-ray emission from Sgr A*.

scholarly journals What is Sgr A∗?

1996 ◽  
Vol 169 ◽  
pp. 169-180
Author(s):  
H. Falcke
Keyword(s):  
Black Hole ◽  
Central Star ◽  
Solar Mass ◽  
M 10 ◽  
Spectrum Radio ◽  
The Galaxy ◽  
Kinematic Studies ◽  
Sgr A ◽  
Unusual Appearance ◽  
Stellar Kinematic

Sgr A∗ is the unique 1 Jy flat spectrum radio point source located at the dynamical center of the Galaxy and in the very center of the central star cluster (Eckart et al. 1993). Due to its unusual appearance it has long been speculated that this source is powered by a supermassive black hole–an object whose presence has been suspected to reside in the nuclei of many other galaxies as well. Its mass is believed to be as large as M• ∼ 2 m 106M⊙ (e.g. Genzel & Townes 1987) while a lower limit of M• > 200–2000M⊙ can be inferred from the low proper motion of Sgr A∗ (Backer – this volume). The currently best dynamical arguments for the million solar mass black hole stem from detailed stellar kinematic studies (Haller et al. 1995).

scholarly journals Modelling the thermal X-ray emission around the Galactic centre from colliding Wolf-Rayet winds

2016 ◽  
Vol 12 (S329) ◽  
pp. 443-443
Author(s):  
Christopher M. P. Russell ◽  
Q. Daniel Wang ◽  
Jorge Cuadra
Keyword(s):  
Black Hole ◽  
Thermal Emission ◽  
Spectral Shape ◽  
Galactic Centre ◽  
Hydrodynamic Simulations ◽  
Dominant Source ◽  
X Ray ◽  
Hot Gas ◽  
Supermassive Black Hole ◽  
Sgr A

AbstractWe compute the thermal X-ray emission from hydrodynamic simulations of the 30 Wolf-Rayet (WR) stars orbiting within a parsec of Sgr A*, with the aim of interpreting the Chandra X-ray observations of this region. The model well reproduces the spectral shape of the observations, indicating that the shocked WR winds are the dominant source of this thermal emission. The model X-ray flux is tied to the strength of the Sgr A* outflow, which clears out hot gas from the vicinity of Sgr A*. A moderate outflow best fits the present-day observations, even though this supermassive black hole (SMBH) outflow ended ~100 yr ago.

scholarly journals Accretion of stellar winds onto Sgr A*

2006 ◽  
Vol 2 (S238) ◽  
pp. 191-194
Author(s):  
Jorge Cuadra ◽  
Sergei Nayakshin
Keyword(s):  
Black Hole ◽  
Numerical Study ◽  
Stellar Dynamics ◽  
Galactic Centre ◽  
Stellar Winds ◽  
Massive Black Hole ◽  
X Ray ◽  
3 Dimensional ◽  
Sgr A ◽  
Slow Wind

AbstractWe report a 3-dimensional numerical study of the accretion of stellar winds onto Sgr A*, the super-massive black hole at the centre of our Galaxy. Compared with previous investigations, we allow the stars to be on realistic orbits, include the recently discovered slow wind sources, and allow for optically thin radiative cooling. We first show the strong influence of the stellar dynamics on the accretion onto the central black hole. We then present more realistic simulations of Sgr A* accretion and find that the slow winds shock and rapidly cool, forming cold gas clumps and filaments that coexist with the hot X-ray emitting gas. The accretion rate in this case is highly variable on time-scales of tens to hundreds of years. Such variability can in principle lead to a strongly non-linear response through accretion flow physics not resolved here, making Sgr A* an important energy source for the Galactic centre.

scholarly journals Spectroscopy of Stellar X-ray Sources in the Magellanic Clouds

1984 ◽  
Vol 108 ◽  
pp. 305-312
Author(s):  
J. B. Hutchings
Keyword(s):  
Black Hole ◽  
Magellanic Cloud ◽  
Active Galaxies ◽  
Magellanic Clouds ◽  
Dwarf Stars ◽  
X Ray ◽  
Preliminary Comparison ◽  
The Galaxy ◽  
Optical Identifications ◽  
X Ray Binaries

In the Magellanic Clouds, about 75 candidate stellar X-ray sources have been detected. Most of these positions have now been investigated and optical identifications made for ~ 50%. The majority of sources are foreground dwarf stars or background active galaxies. Detailed investigations exist for 3 SMC sources and 6 LMC sources. It is possible to make a preliminary comparison with the population of galactic X-ray sources. The Magellanic Cloud X-ray binaries have a number of unique or remarkable properties and the most important ones are presented and discussed. These include the most rapid pulsars (SMC X-1, 0538–66), the possible precessing disk in LMC X-4, and the black hole candidates LMC X-3, LMC X-1. The properties of these objects relate to the evolution of stars in the Magellanic Clouds and how it differs from the Galaxy.

scholarly journals X-Ray Heated Accretion Discs Around Stellar Mass Black Holes

2004 ◽  
Vol 194 ◽  
pp. 200-201
Author(s):  
Ivan Hubeny ◽  
Dayal T. Wickramasinghe
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Vertical Structure ◽  
Black Body ◽  
Incident Radiation ◽  
Accretion Discs ◽  
Distribution Models ◽  
Solar Mass ◽  
X Ray ◽  
Low Mass

We investigate the effects of irradiation on the vertical structure of accretion discs around black holes and its impact on the emergent energy distribution. Models are presented for a 10 Solar mass black hole in a low mass X-ray binary assuming a black body spectrum for the incident radiation. We show that for a disc annulus at a given radius, the spectra become increasingly distorted as the incident flux increases relative to the viscously generated heating flux in the disc. Significant effects are apparent for rings even at distances of ~ 10,000 Schwarzschild radii from the black hole for realistic dilution factors.

scholarly journals Glimpses of the past activity of Sgr A★ inferred from X-ray echoes in Sgr C

2018 ◽  
Vol 610 ◽  
pp. A34 ◽  
Author(s):  
D. Chuard ◽  
R. Terrier ◽  
A. Goldwurm ◽  
M. Clavel ◽  
S. Soldi ◽  
...  
Keyword(s):  
Monte Carlo ◽  
Black Hole ◽  
Monte Carlo Model ◽  
Line Of Sight ◽  
X Rays ◽  
X Ray ◽  
Supermassive Black Hole ◽  
The Past ◽  
Sgr A ◽  
Past Activity

Context. For a decade now, evidence has accumulated that giant molecular clouds located within the central molecular zone of our Galaxy reflect X-rays coming from past outbursts of the Galactic supermassive black hole. However, the number of illuminating events as well as their ages and durations are still unresolved questions. Aims. We aim to reconstruct parts of the history of the supermassive black hole Sgr A★ by studying this reflection phenomenon in the molecular complex Sgr C and by determining the line-of-sight positions of its main bright substructures. Methods. Using observations made with the X-ray observatories XMM-Newton and Chandra and between 2000 and 2014, we investigated the variability of the reflected emission, which consists of a Fe Kα line at 6.4 keV and a Compton continuum. We carried out an imaging and a spectral analysis. We also used a Monte Carlo model of the reflected spectra to constrain the line-of-sight positions of the brightest clumps, and hence to assign an approximate date to the associated illuminating events. Results. We show that the Fe Kα emission from Sgr C exhibits significant variability in both space and time, which confirms its reflection origin. The most likely illuminating source is Sgr A★. On the one hand, we report two distinct variability timescales, as one clump undergoes a sudden rise and fall in about 2005, while two others vary smoothly throughout the whole 2000–2014 period. On the other hand, by fitting the Monte Carlo model to the data, we are able to place tight constraints on the 3D positions of the clumps. These two independent approaches provide a consistent picture of the past activity of Sgr A★, since the two slowly varying clumps are located on the same wavefront, while the third (rapidly varying) clump corresponds to a different wavefront, that is, to a different illuminating event. Conclusions. This work shows that Sgr A★ experienced at least two powerful outbursts in the past 300 yrs, and for the first time, we provide an estimation of their age. Extending this approach to other molecular complexes, such as Sgr A, will allow this two-event scenario to be tested further.

scholarly journals 10.2. High proper motions in the vicinity of Sgr A∗: unambiguous evidence for a massive central black hole

1998 ◽  
Vol 184 ◽  
pp. 433-434
Author(s):  
A. M. Ghez ◽  
B. L. Klein ◽  
C. McCabe ◽  
M. Morris ◽  
E. E. Becklin
Keyword(s):  
Black Hole ◽  
Milky Way ◽  
Galactic Center ◽  
Robust Method ◽  
Proper Motions ◽  
Central Black Hole ◽  
Milky Way Galaxy ◽  
The Galaxy ◽  
Sgr A

Although the notion that the Milky Way galaxy contains a supermassive central black hole has been around for more than two decades, it has been difficult to prove that one exists. The challenge is to assess the distribution of matter in the few central parsecs of the Galaxy. Assuming that gravity is the dominant force, the motion of the stars and gas in the vicinity of the putative black hole offers a robust method for accomplishing this task, by revealing the mass interior to the radius of the objects studied. Thus objects located closest to the Galactic Center provide the strongest constraints on the black hole hypothesis.

scholarly journals A 400-solar-mass black hole in the galaxy M82

Nature ◽  
2014 ◽  
Vol 513 (7516) ◽  
pp. 74-76 ◽  
Author(s):  
Dheeraj R. Pasham ◽  
Tod E. Strohmayer ◽  
Richard F. Mushotzky
Keyword(s):  
Black Hole ◽  
Solar Mass ◽  
The Galaxy

scholarly journals Colliding stellar winds: X-ray emission and instabilities

1995 ◽  
Vol 163 ◽  
pp. 486-494
Author(s):  
Ian R. Stevens
Keyword(s):  
Stellar Winds ◽  
Radiation Hydrodynamics ◽  
Hydrodynamic Simulations ◽  
X Ray ◽  
Radiation Fields ◽  
Basic Physics ◽  
Hydrodynamic Calculations ◽  
Basic Characteristics ◽  
Colliding Winds ◽  
Insight Into

Colliding stellar winds are an important part of early-type binaries. In this paper I discuss the phenomenon, concentrating mainly on the basic hydrodynamics of colliding winds, and the physics of X-ray emission. The following topics are covered:1) Basic physics: The basic characteristics of the shock-produced thermal X-ray emission, and discuss general trends of X-ray emission from colliding wind binaries (CWBs).2) Hydrodynamic simulations: Recent calculations have found that the interface in colliding winds is usually dynamically unstable, with three distinct instabilities.3) Gamma Velorum: recent ROSAT observations give much insight into colliding winds. I discuss recent hydrodynamic calculations pertaining to these observations.4) Radiation Hydrodynamics in CWBs: Recent calculations have included the effects of both radiation fields on the wind hydrodynamics in colliding wind systems.

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