scholarly journals IMAGES OF THE RADIATIVELY INEFFICIENT ACCRETION FLOW SURROUNDING A KERR BLACK HOLE: APPLICATION IN Sgr A*

2009 ◽  
Vol 699 (1) ◽  
pp. 722-731 ◽  
Author(s):  
Ye-Fei Yuan ◽  
Xinwu Cao ◽  
Lei Huang ◽  
Zhi-Qiang Shen
Keyword(s):  
Black Hole ◽  
Kerr Black Hole ◽  
Accretion Flow ◽  
Sgr A

scholarly journals Influence of the geometric configuration of accretion flow on the black hole spin dependence of relativistic acoustic geometry

2018 ◽  
Vol 27 (03) ◽  
pp. 1850023 ◽  
Author(s):  
Pratik Tarafdar ◽  
Tapas K. Das
Keyword(s):  
Black Hole ◽  
Kerr Black Hole ◽  
Geometric Configuration ◽  
Surface Gravity ◽  
Linear Perturbation ◽  
Flow Profile ◽  
White Hole ◽  
Accretion Flow ◽  
Black Hole Spin ◽  
General Relativistic

Linear perturbation of general relativistic accretion of low angular momentum hydrodynamic fluid onto a Kerr black hole leads to the formation of curved acoustic geometry embedded within the background flow. Characteristic features of such sonic geometry depend on the black hole spin. Such dependence can be probed by studying the correlation of the acoustic surface gravity [Formula: see text] with the Kerr parameter [Formula: see text]. The [Formula: see text]–[Formula: see text] relationship further gets influenced by the geometric configuration of the accretion flow structure. In this work, such influence has been studied for multitransonic shocked accretion where linear perturbation of general relativistic flow profile leads to the formation of two analogue black hole-type horizons formed at the sonic points and one analogue white hole-type horizon which is formed at the shock location producing divergent acoustic surface gravity. Dependence of the [Formula: see text]–[Formula: see text] relationship on the geometric configuration has also been studied for monotransonic accretion, over the entire span of the Kerr parameter including retrograde flow. For accreting astrophysical black holes, the present work thus investigates how the salient features of the embedded relativistic sonic geometry may be determined not only by the background spacetime, but also by the flow configuration of the embedding matter.

scholarly journals Limitations of the pseudo-Newtonian approach in studying the accretion flow around a Kerr black hole

2018 ◽  
Vol 98 (8) ◽  
Author(s):  
Indu K. Dihingia ◽  
Santabrata Das ◽  
Debaprasad Maity ◽  
Sayan Chakrabarti
Keyword(s):  
Black Hole ◽  
Kerr Black Hole ◽  
Accretion Flow

ACCRETION PROBLEM IN A KERR BLACK HOLE GEOMETRY VIEWED AS FLOWS IN CONVERGING–DIVERGING DUCTS

2010 ◽  
Vol 19 (13) ◽  
pp. 2059-2069
Author(s):  
K. CHAKRABARTI ◽  
M. M. MAJUMDAR ◽  
SANDIP K. CHAKRABARTI
Keyword(s):  
Black Hole ◽  
Angular Momentum ◽  
Mach Number ◽  
Cross Sections ◽  
Kerr Black Hole ◽  
Flat Space ◽  
Accretion Flow ◽  
Black Hole Accretion ◽  
Hole Geometry ◽  
Hole Accretion

Accretion flow on a horizon is supersonic, no matter what the flow angular momentum or the spin of the black hole is. This means that a black hole accretion can always be viewed as a flow in a flat space–time through one or more convergent–divergent ducts. In this paper, we study how the area of cross-sections must vary in order that the flow has the same properties in both systems. We show that the accretion flow experiencing a shock is equivalent to having two ducts connected back-to-back, both with a neck where the flow becomes supersonic. We study the pressure and Mach number variations for corotating, contrarotating flows and flows around a black hole with evolving spin.

scholarly journals How to tell an accreting boson star from a black hole

2020 ◽  
Vol 497 (1) ◽  
pp. 521-535 ◽  
Author(s):  
Hector Olivares ◽  
Ziri Younsi ◽  
Christian M Fromm ◽  
Mariafelicia De Laurentis ◽  
Oliver Porth ◽  
...  
Keyword(s):  
Black Hole ◽  
Radiative Transfer ◽  
Event Horizon ◽  
Polar Regions ◽  
Radio Observations ◽  
Accretion Flow ◽  
Supermassive Black Hole ◽  
General Relativistic ◽  
Sgr A ◽  
Magnetohydrodynamic Simulations

ABSTRACT The capability of the Event Horizon Telescope (EHT) to image the nearest supermassive black hole candidates at horizon-scale resolutions offers a novel means to study gravity in its strongest regimes and to test different models for these objects. Here, we study the observational appearance at 230 GHz of a surfaceless black hole mimicker, namely a non-rotating boson star, in a scenario consistent with the properties of the accretion flow on to Sgr A*. To this end, we perform general relativistic magnetohydrodynamic simulations followed by general relativistic radiative transfer calculations in the boson star space–time. Synthetic reconstructed images considering realistic astronomical observing conditions show that, despite qualitative similarities, the differences in the appearance of a black hole – either rotating or not – and a boson star of the type considered here are large enough to be detectable. These differences arise from dynamical effects directly related to the absence of an event horizon, in particular, the accumulation of matter in the form of a small torus or a spheroidal cloud in the interior of the boson star, and the absence of an evacuated high-magnetization funnel in the polar regions. The mechanism behind these effects is general enough to apply to other horizonless and surfaceless black hole mimickers, strengthening confidence in the ability of the EHT to identify such objects via radio observations.

scholarly journals Scale-invariance of black hole accretion: modelling emission from a black hole X-ray binary with relativistic accretion flow simulations

2019 ◽  
Vol 490 (4) ◽  
pp. 5353-5358
Author(s):  
M Mościbrodzka
Keyword(s):  
Black Hole ◽  
Near Infrared ◽  
Thermal Emission ◽  
Broad Band ◽  
Scale Invariant ◽  
X Ray ◽  
Accretion Flow ◽  
Black Hole Accretion ◽  
Sgr A ◽  
Hole Accretion

ABSTRACT We model the non-thermal emission spectrum of the extremely sub-Eddington X-ray binary system A0620-00. It is believed that this non-thermal emission is produced by radiatively inefficient ‘quiescent’ accretion on to a stellar-mass black hole present in the system. We post-process general relativistic magnetohydrodynamics (GRMHD) simulations with multiwavelength, fully polarized, relativistic radiative transfer calculations to predict broad-band spectra and emission polarization levels for a range of electron models and accretion rates. We find that a model with strong coupling of electrons and ions in the accretion disc and accretion rate of only $\dot{M}=3\times 10^{-13} \, \rm [M_\odot \, yr^{-1}]$ is able to recover the observed X-ray spectral slope, as well as the excess of linear polarization detected in the source in the near-infrared (NIR)/optical bands. Our models constrain the spectral properties of a putative relativistic jet produced in this system. In addition, we show that the magnetized winds from our hot accretion flow carry away a small fraction of the orbital angular momentum of the binary, which is unable to explain the observed rapid orbital decay of the system. GRMHD simulations similar to the present ones are often used to explain emission from sub-Eddington supermassive black holes in Sgr A* or M87; the present simulations allow us to test whether some aspects of quiescent black hole accretion are scale-invariant.

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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