scholarly journals Radiation from Advection-Dominated Flows

1998 ◽  
Vol 188 ◽  
pp. 417-418
Author(s):  
T. Manmoto
Keyword(s):  
Black Holes ◽  
Compact Objects ◽  
Radiation Process ◽  
Massive Black Hole ◽  
Accretion Flow ◽  
Accretion Flows ◽  
Accretion Process ◽  
Self Consistent ◽  
Consistent Solution ◽  
Sgr A

Advection-dominated accretion flow (hereafter ADAF) is the only self-consistent solution to describe the optically thin accretion flows around compact objects. The main feature of ADAF is that the dynamics of the flow is dominated by accretion process rather than radiation process. As a result of advection domination, the luminosity of ADAFs is very low. Coupled with the existence of the event horizon, ADAF has been successfully applied to the dim accretion black holes such as central core of our Galaxy: Sgr A*. In this issue, we calculate the spectrum radiated from the optically thin ADAFs and show that the observed spectrum of Sgr A* is explained with the accretion massive black hole.

scholarly journals Energy Release and Transport Processes in the Centres of Galaxies

2001 ◽  
Vol 205 ◽  
pp. 10-17
Author(s):  
Roger Blandford
Keyword(s):  
Black Holes ◽  
Large Mass ◽  
Transport Processes ◽  
Reasonable Doubt ◽  
Massive Black Hole ◽  
Massive Black Holes ◽  
Disk Formation ◽  
Accretion Flows ◽  
Mass Outflow ◽  
Sgr A

Observations over the past decade have verified, beyond reasonable doubt, that most galactic nuclei contain massive black holes. Hole masses are being measured and firm evidence for spin is being sought. Attention is now returning to the study of how gas flows around black holes and how energy is released both from the accreting gas and from the hole itself in the form of radiation, relativistic jets and non-relativistic, hydromagnetic winds. Some of the different possibilities currently under investigation are briefly reviewed and some recent clues from radio scintillation, polarization and X-ray observations are discussed. It is argued that observations of persistent circular polarisation in Sgr A* support the presence of an ordered disk magnetic field. It is also conjectured that adiabatic, sub- and super-critical accretion flows are demand-limited, not supply-driven and are associated with large mass outflow as appears to be the case in Sgr A*. This principle may have to be modified when a massive black hole forms in a protogalaxy and this modification may account for the proposed hole mass-bulge velocity dispersion relation. The final stages of this process may release sufficient wind energy from the nucleus to prevent disk formation.

scholarly journals The Process of Stellar Tidal Disruption by Supermassive Black Holes

2021 ◽  
Vol 217 (3) ◽  
Author(s):  
E. M. Rossi ◽  
N. C. Stone ◽  
J. A. P. Law-Smith ◽  
M. Macleod ◽  
G. Lodato ◽  
...  
Keyword(s):  
Black Holes ◽  
Initial Conditions ◽  
Numerical Models ◽  
Binary Star ◽  
Tidal Disruption ◽  
Massive Black Hole ◽  
Accretion Flows ◽  
Simple Order ◽  
Order Of Magnitude ◽  
A Chain

AbstractTidal disruption events (TDEs) are among the brightest transients in the optical, ultraviolet, and X-ray sky. These flares are set into motion when a star is torn apart by the tidal field of a massive black hole, triggering a chain of events which is – so far – incompletely understood. However, the disruption process has been studied extensively for almost half a century, and unlike the later stages of a TDE, our understanding of the disruption itself is reasonably well converged. In this Chapter, we review both analytical and numerical models for stellar tidal disruption. Starting with relatively simple, order-of-magnitude physics, we review models of increasing sophistication, the semi-analytic “affine formalism,” hydrodynamic simulations of the disruption of polytropic stars, and the most recent hydrodynamic results concerning the disruption of realistic stellar models. Our review surveys the immediate aftermath of disruption in both typical and more unusual TDEs, exploring how the fate of the tidal debris changes if one considers non-main sequence stars, deeply penetrating tidal encounters, binary star systems, and sub-parabolic orbits. The stellar tidal disruption process provides the initial conditions needed to model the formation of accretion flows around quiescent massive black holes, and in some cases may also lead to directly observable emission, for example via shock breakout, gravitational waves or runaway nuclear fusion in deeply plunging TDEs.

scholarly journals The Fermi bubbles inflated by winds from the accretion flow in Sgr A*

2014 ◽  
Vol 10 (S312) ◽  
pp. 137-138
Author(s):  
Guobin Mou
Keyword(s):  
Numerical Simulations ◽  
Three Dimensional ◽  
Small Scale ◽  
Observational Constraints ◽  
Accretion Flow ◽  
Accretion Flows ◽  
The Past ◽  
Sgr A ◽  
Hydrodynamical Simulations

AbstractBy performing three-dimensional hydrodynamical simulations, we show that the Fermi bubbles could be inflated by winds launched from the “past” hot accretion flow in Sgr A*. The parameters of the accretion flow required in the model are consistent with those obtained independently from other observational constraints. The wind parameters are taken from small scale MHD numerical simulations of hot accretion flows.

scholarly journals Can we see pulsars around Sgr A⋆? The latest searches with the Effelsberg telescope.

2012 ◽  
Vol 8 (S291) ◽  
pp. 382-384
Author(s):  
R. P. Eatough ◽  
M. Kramer ◽  
B. Klein ◽  
R. Karuppusamy ◽  
D. J. Champion ◽  
...  
Keyword(s):  
Binary Systems ◽  
Compact Objects ◽  
Galactic Centre ◽  
Radio Waves ◽  
Test Bed ◽  
Radio Pulsars ◽  
Massive Black Hole ◽  
Centre Region ◽  
Sgr A ◽  
Temporal Broadening

AbstractRadio pulsars in relativistic binary systems are unique tools to study the curved space-time around massive compact objects. The discovery of a pulsar closely orbiting the super-massive black hole at the centre of our Galaxy, Sgr A⋆, would provide a superb test-bed for gravitational physics. To date, the absence of any radio pulsar discoveries within a few arc minutes of Sgr A⋆ has been explained by one principal factor: extreme scattering of radio waves caused by inhomogeneities in the ionized component of the interstellar medium in the central 100 pc around Sgr A⋆. Scattering, which causes temporal broadening of pulses, can only be mitigated by observing at higher frequencies. Here we describe recent searches of the Galactic centre region performed at a frequency of 18.95 GHz with the Effelsberg radio telescope.

scholarly journals Transonic structure of slowly rotating accretion flows with shocks around black holes

2016 ◽  
Vol 12 (S324) ◽  
pp. 23-26
Author(s):  
Petra Suková ◽  
Szymon Charzyński ◽  
Agnieszka Janiuk
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Angular Momentum ◽  
Time Scale ◽  
Mass Scale ◽  
Schwarzschild Black Hole ◽  
Transonic Flows ◽  
Accretion Flows ◽  
2D Structure ◽  
Sgr A

AbstractWe present recent results of the studies of low angular momentum accretion of matter onto Schwarzschild black hole using fully relativistic numerical simulations. We compare the resulting 2D structure of transonic flows with results of 1D pseudo-Newtonian computations of non-magnetized flow. The research has observable consequences on black holes on the whole mass scale, in particular it is related to the time-scale and shape of luminosity flares in Sgr A* or to the evolution of QPO frequency during outbursts of microquasars.

scholarly journals Towards self-consistent modelling of the Sgr A* accretion flow: linking theory and observation

2016 ◽  
Vol 466 (2) ◽  
pp. 1477-1490 ◽  
Author(s):  
Shawn R. Roberts ◽  
Yan-Fei Jiang姜燕飞 ◽  
Q. Daniel Wang ◽  
Jeremiah P. Ostriker
Keyword(s):  
Accretion Flow ◽  
Self Consistent ◽  
Sgr A

scholarly journals Simulating the pericentre passage of the Galactic centre star S2

2018 ◽  
Vol 616 ◽  
pp. L8 ◽  
Author(s):  
M. Schartmann ◽  
A. Burkert ◽  
A. Ballone
Keyword(s):  
Power Law ◽  
Stellar Wind ◽  
Adaptive Mesh Refinement ◽  
Mass Loss Rate ◽  
Galactic Centre ◽  
Massive Black Hole ◽  
X Ray ◽  
Flow Models ◽  
Accretion Flow ◽  
Sgr A

Context. Our knowledge of the density distribution of the accretion flow around Sgr A* – the massive black hole (BH) at our Galactic centre (GC) – relies on two measurements only: one at a distance of a few Schwarzschild radii (Rs) and one at roughly 105 Rs, which are usually bridged by a power law, which is backed by magnetohydrodynamical simulations. The so-called S2 star reached its closest approach to the massive BH at around 1500 Rs in May 2018. It has been proposed that the interaction of its stellar wind with the high-density accretion flow at this distance from Sgr A* will lead to a detectable, month-long X-ray flare. Aims. Our goal is to verify whether or not the S2 star wind can be used as a diagnostic tool to infer the properties of the accretion flow towards Sgr A* at its pericentre (an unprobed distance regime), putting important constraints on BH accretion flow models. Methods. We run a series of three-dimensional adaptive mesh refinement simulations with the help of the RAMSES code which include the realistic treatment of the interaction of S2’s stellar wind with the accretion flow along its orbit and – apart from hydrodynamical and thermodynamical effects – include the tidal interaction with the massive BH. These are post-processed to derive the X-ray emission in the observable 2–10 keV window. Results. No significant excess of X-ray emission from Sgr A* is found for typical accretion flow models. A measurable excess is produced for a significantly increased density of the accretion flow. This can, however, be ruled out for standard power-law accretion flow models as in this case the thermal X-ray emission without the S2 wind interaction would already exceed the observed quiescent luminosity. Only a significant change of the wind parameters (increased mass loss rate and decreased wind velocity) might lead to an (marginally) observable X-ray flaring event. Conclusion. Even the detection of an (month-long) X-ray flare during the pericentre passage of the S2 star would not allow for strict constraints to be put on the accretion flow around Sgr A* due to the degeneracy caused by the dependence on multiple parameters (of the accretion flow model as well as the stellar wind).

Ratio of the jet power to the bolometric luminosity of the disk during accretion onto a black hole

2019 ◽  
Vol 28 (02) ◽  
pp. 1950032 ◽  
Author(s):  
S. V. Bogovalov
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Kinetic Energy ◽  
Energy Flux ◽  
Gravitational Energy ◽  
Disk Accretion ◽  
Massive Black Hole ◽  
Bolometric Luminosity ◽  
Sgr A ◽  
Jet Power

Disk accretion onto black holes is accompanied by collimated outflows (jets). In active galactic nuclei (AGN), the kinetic energy flux of the jet (jet power or kinetic luminosity) may exceed the bolometric luminosity of the disk by a few orders of magnitude. This may be explained in the framework of the so-called “cold” disk accretion when the only source of the AGN energy is the energy released by accretion. The radiation from the disk is suppressed because the disk wind carries out almost all the angular momentum and the gravitational energy of the accreting material. In this paper, we calculate the “unavoidable” radiation from the “cold” disk and the ratio of the kinetic energy power of the outflow to the bolometric luminosity of the accretion disk around a super massive black hole in the framework of the Shakura and Sunyaev paradigm of an optically thick [Formula: see text]-disk. The exploration of the Fundamental Plane of Black Holes allows us to obtain equations that define the bolometric luminosity and the ratio of the luminosities as functions of the black hole mass and accretion rate. The application of our equations in the case of the M87 jet demonstrates good agreement with observations. In the case of Sgr A*, these equations allow us to predict the kinetic energy flux from the disk around the Galactic supermassive black hole.

scholarly journals HYDRODYNAMICAL STUDY OF ADVECTIVE ACCRETION FLOW AROUND NEUTRON STARS

2002 ◽  
Vol 11 (08) ◽  
pp. 1305-1319 ◽  
Author(s):  
BANIBRATA MUKHOPADHYAY
Keyword(s):  
Magnetic Field ◽  
Neutron Stars ◽  
Accretion Disk ◽  
White Dwarfs ◽  
The Other ◽  
Hydrodynamic Equations ◽  
Accretion Flow ◽  
Accretion Flows ◽  
Accretion Process ◽  
Inner Region

Here we study the accretion process around neutron stars, especially for the cases where shock does form in the accretion disk. In case of accretion flows around a black hole, close to the horizon the matter is supersonic. On the other hand for the case of neutron stars and white dwarfs, matter must be subsonic close to the inner boundary. So the nature of the inflowing matter around neutron stars and white dwarfs are strictly different from that around black holes in the inner region of the disk. Here we discuss a few phenomena and the corresponding solutions of hydrodynamic equations of matter in an accretion disk around slowly rotating neutron stars without magnetic field.

scholarly journals Blob formation and ejection from the radiative inefficient accretion flow around massive black hole

2020 ◽  
Author(s):  
Tian-Le Zhao ◽  
Ye-Fei Yuan ◽  
Rajiv Kumar
Keyword(s):  
Magnetic Field ◽  
Black Hole ◽  
Current Sheet ◽  
Magnetic Energy ◽  
Small Scale ◽  
Central Black Hole ◽  
Massive Black Hole ◽  
Accretion Flow ◽  
Black Hole Accretion ◽  
Sgr A

Abstract We study the small scale magnetic reconnection above the radiative inefficient accretion flow around massive black hole via 2D magnetohydrodynamics (MHD) numerical simulation, in order to model the blob formation and ejection from the accretion flow around Sgr A*. The connection of both the newly emerging magnetic field and the pre-existing magnetic field is investigated to check whether blobs could be driven in the environment of black hole accretion disk. After the magnetic connection, both the velocity and temperature of the plasma can be comparable to the inferred physical properties at the base of the observed blob ejection. For illustration, three small boxes which are located within 40 Schwarzschild radii from the central black hole are chosen as our simulation areas. At the beginning of the reconnections, the fluid is pulled toward the central black hole due to the gravitational attraction, and the current sheet produced by the reconnection is also pulled toward the same direction, consequently, the resulting outflows move both upward and toward the symmetry axis of the central black hole. Eventually, huge blobs appear, which supports the catastrophe model of episodic jets (Yuan et al. 2009a). It is also found that the closer to the black hole the magnetic connection happens, the higher the converting efficiency of the magnetic energy into the heat and kinetic energy. For these inner blobs, they have vortex structure due to the Kelvin-Helmholtz instability which happens along the current sheet separating the fluids with different speed.

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