STELLAR DYNAMICS IN A GALACTIC CENTRE SURROUNDED BY AN ACCRETION DISC

2002 ◽  
pp. 85-110 ◽  
Author(s):  
VLADIMÍR KARAS ◽  
LADISLAV ŠUBR ◽  
MIROSLAV ŠLECHTA
Keyword(s):  
Stellar Dynamics ◽  
Accretion Disc ◽  
Galactic Centre

scholarly journals Feeding of active galactic nuclei by dynamical perturbations

2019 ◽  
Vol 492 (1) ◽  
pp. 603-614
Author(s):  
Matas Tartėnas ◽  
Kastytis Zubovas
Keyword(s):  
Active Galactic Nuclei ◽  
Feeding Rate ◽  
Galactic Nuclei ◽  
Accretion Disc ◽  
High Impact ◽  
Galactic Centre ◽  
Supermassive Black Hole ◽  
Disc Model ◽  
Limiting Values ◽  
Significant Mass

ABSTRACT There possibly was an active galactic nuclei (AGN) episode in the Galactic Centre (GC) about 6 Myr ago, powerful enough to produce the Fermi bubbles. We present numerical simulations of a possible scenario giving rise to an activity episode: a collision between a central gas ring surrounding the supermassive black hole (SMBH) and an infalling molecular cloud. We investigate different initial collision angles between the cloud and the ring. We follow the hydrodynamical evolution of the system following the collision using gadget-3 hybrid N-body/SPH code and calculate the feeding rate of the SMBH accretion disc. This rate is then used as an input for a 1D thin α-disc model in order to calculate the AGN luminosity. By varying the disc feeding radii, we determine the limiting values for possible AGN accretion disc luminosity. Small angle collisions do not result in significant mass transport to the centre of the system, while models with highest collision angles transport close to $40{{\ \rm per\ cent}}$ of the initial matter to the accretion disc. Even with ring and cloud masses equal to $10^4 \, {\rm M_{\odot }}$, which is the lower limit of present-day mass of the circumnuclear ring in the GC, the energy released over an interval of 1.5 Myr can produce $\sim 10{{\ \rm per\ cent}}$ of that required to inflate the Fermi bubbles. If the gas ring in the GC 6 Myr ago had a mass of at least $10^5 \, {\rm M_{\odot }}$, our proposed scenario can explain the formation of the Fermi bubbles. We estimate that such high-impact collisions might occur once every ∼108 yr in our Galaxy.

scholarly journals Stellar dynamics in the Galactic Centre: proper motions and anisotropy

2000 ◽  
Vol 317 (2) ◽  
pp. 348-374 ◽  
Author(s):  
R. Genzel ◽  
C. Pichon ◽  
A. Eckart ◽  
O. E. Gerhard ◽  
T. Ott
Keyword(s):  
Stellar Dynamics ◽  
Galactic Centre ◽  
Proper Motions

scholarly journals The distribution of stars around the Milky Way’s central black hole

2017 ◽  
Vol 609 ◽  
pp. A28 ◽  
Author(s):  
H. Baumgardt ◽  
P. Amaro-Seoane ◽  
R. Schödel
Keyword(s):  
Black Hole ◽  
Adaptive Optics ◽  
Near Infrared ◽  
Stellar Dynamics ◽  
Galactic Centre ◽  
Test Case ◽  
Central Black Hole ◽  
Massive Black Hole ◽  
Giant Stars ◽  
Sgr A

Context. The distribution of stars around a massive black hole (MBH) has been addressed in stellar dynamics for the last four decades by a number of authors. Because of its proximity, the centre of the Milky Way is the only observational test case where the stellar distribution can be accurately tested. Past observational work indicated that the brightest giants in the Galactic centre (GC) may show a density deficit around the central black hole, not a cusp-like distribution, while we theoretically expect the presence of a stellar cusp. Aims. We here present a solution to this long-standing problem. Methods. We performed direct-summation N-body simulations of star clusters around massive black holes and compared the results of our simulations with new observational data of the GC’s nuclear cluster. Results. We find that after a Hubble time, the distribution of bright stars as well as the diffuse light follow power-law distributions in projection with slopes of Γ ≈ 0.3 in our simulations. This is in excellent agreement with what is seen in star counts and in the distribution of the diffuse stellar light extracted from adaptive-optics (AO) assisted near-infrared observations of the GC. Conclusions. Our simulations also confirm that there exists a missing giant star population within a projected radius of a few arcsec around Sgr A*. Such a depletion of giant stars in the innermost 0.1 pc could be explained by a previously present gaseous disc and collisions, which means that a stellar cusp would also be present at the innermost radii, but in the form of degenerate compact cores.

scholarly journals Making massive stars in the Galactic Centre via accretion on to low-mass stars within an accretion disc

2020 ◽  
Vol 498 (3) ◽  
pp. 3452-3456
Author(s):  
Melvyn B Davies ◽  
Doug N C Lin
Keyword(s):  
Black Hole ◽  
Massive Stars ◽  
Mass Function ◽  
Accretion Disc ◽  
Galactic Centre ◽  
Low Mass Stars ◽  
Stellar Cluster ◽  
Supermassive Black Hole ◽  
Tidal Forces ◽  
Low Mass

ABSTRACT The origin of the population of very massive stars observed within ∼0.4 pc of the supermassive black hole in the Galactic Centre is a mystery. Tidal forces from the black hole would likely inhibit in situ star formation whilst the youth of the massive stars would seem to exclude formation elsewhere followed by transportation (somehow) into the Galactic Centre. Here, we consider a third way to produce these massive stars from the lower mass stars contained in the nuclear stellar cluster which surrounds the supermassive black hole. A passing gas cloud can be tidally shredded by the supermassive black hole forming an accretion disc around the black hole. Stars embedded within this accretion disc will accrete gas from the disc via Bondi–Hoyle accretion, where the accretion rate on to a star, $\dot{M}_\star \propto M_\star ^2$. This super-exponential growth of accretion can lead to a steep increase in stellar masses, reaching the required 40–50 M⊙ in some cases. The mass growth rate depends sensitively on the stellar orbital eccentricities and their inclinations. The evolution of the orbital inclinations and/or their eccentricities as stars are trapped by the disc, and their orbits are circularized, will increase the number of massive stars produced. Thus accretion on to low-mass stars can lead to a top heavy stellar mass function in the Galactic Centre and other galactic nuclei. The massive stars produced will pollute the environment via supernova explosions and potentially produce compact binaries whose mergers may be detectable by the LIGO–VIRGO gravitational waves observatories.

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.

Interstellar gas in the central region of the Galaxy

1967 ◽  
Vol 31 ◽  
pp. 239-251 ◽  
Author(s):  
F. J. Kerr
Keyword(s):  
Central Region ◽  
Galactic Plane ◽  
Neutral Hydrogen ◽  
Continuum Emission ◽  
Galactic Centre ◽  
Interstellar Gas ◽  
Hydrogen Recombination ◽  
The Galaxy ◽  
Centre Region ◽  
The Relationship

A review is given of information on the galactic-centre region obtained from recent observations of the 21-cm line from neutral hydrogen, the 18-cm group of OH lines, a hydrogen recombination line at 6 cm wavelength, and the continuum emission from ionized hydrogen.Both inward and outward motions are important in this region, in addition to rotation. Several types of observation indicate the presence of material in features inclined to the galactic plane. The relationship between the H and OH concentrations is not yet clear, but a rough picture of the central region can be proposed.

Progress report on 21-cm observations at low latitude between longitudes (l 11) 0° and 66°

1967 ◽  
Vol 31 ◽  
pp. 177-179
Author(s):  
W. W. Shane
Keyword(s):  
Preliminary Report ◽  
Progress Report ◽  
Galactic Centre ◽  
Low Latitude ◽  
The Third ◽  
Introductory Lecture ◽  
Centre Region

In the course of several 21-cm observing programmes being carried out by the Leiden Observatory with the 25-meter telescope at Dwingeloo, a fairly complete, though inhomogeneous, survey of the regionl11= 0° to 66° at low galactic latitudes is becoming available. The essential data on this survey are presented in Table 1. Oort (1967) has given a preliminary report on the first and third investigations. The third is discussed briefly by Kerr in his introductory lecture on the galactic centre region (Paper 42). Burton (1966) has published provisional results of the fifth investigation, and I have discussed the sixth in Paper 19. All of the observations listed in the table have been completed, but we plan to extend investigation 3 to a much finer grid of positions.

Observations of the continuum near the galactic centre

1967 ◽  
Vol 31 ◽  
pp. 405
Author(s):  
F. J. Kerr
Keyword(s):  
Galactic Centre ◽  
The Past ◽  
Centre Region ◽  
The Continuum

A continuum survey of the galactic-centre region has been carried out at Parkes at 20 cm wavelength over the areal11= 355° to 5°,b11= -3° to +3° (Kerr and Sinclair 1966, 1967). This is a larger region than has been covered in such surveys in the past. The observations were done as declination scans.

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