scholarly journals Magnetohydrodynamics Simulations of Active Galactic Nucleus Disks and Jets

2020 ◽  
Vol 58 (1) ◽  
pp. 407-439
Author(s):  
Shane W. Davis ◽  
Alexander Tchekhovskoy
Keyword(s):  
Black Hole ◽  
Accretion Disk ◽  
Surrounding Medium ◽  
Observational Constraints ◽  
Disk Model ◽  
Accretion Flow ◽  
Accretion Flows ◽  
Black Hole Spin ◽  
Spiral Density Waves ◽  
Mhd Simulations

There is a broad consensus that accretion onto supermassive black holes and consequent jet formation power the observed emission from active galactic nuclei (AGNs). However, there has been less agreement about how jets form in accretion flows, their possible relationship to black hole spin, and how they interact with the surrounding medium. There have also been theoretical concerns about instabilities in standard accretion disk models and lingering discrepancies with observational constraints. Despite seemingly successful applications to X-ray binaries, the standard accretion disk model faces a growing list of observational constraints that challenge its application to AGNs. Theoretical exploration of these questions has become increasingly reliant on numerical simulations owing to the dynamic nature of these flows and the complex interplay between hydrodynamics, magnetic fields, radiation transfer, and curved spacetime. We conclude the following: ▪  The advent of general relativistic magnetohydrodynamics (MHD) simulations has greatly improved our understanding of jet production and its dependence on black hole spin. ▪  Simulation results show both disks and jets are sensitive to the magnetic flux threading the accretion flow as well as possible misalignment between the angular momentum of the accretion flow and the black hole spin. ▪  Radiation MHD simulations are providing new insights into the stability of luminous accretion flows and highlighting the potential importance of radiation viscosity, UV opacity from atoms, and spiral density waves in AGNs.

scholarly journals The Brightest Point in Accretion Disk and Black Hole Spin: Implication to the Image of Black Hole M87*

Universe ◽  
2019 ◽  
Vol 5 (8) ◽  
pp. 183 ◽  
Author(s):  
Vyacheslav I. Dokuchaev ◽  
Natalia O. Nazarova
Keyword(s):  
Black Hole ◽  
Event Horizon ◽  
Accretion Disk ◽  
Disk Model ◽  
Dark Region ◽  
High Resolution Image ◽  
Supermassive Black Hole ◽  
Black Hole Spin ◽  
The Galaxy ◽  
Expected Position

We propose the simple new method for extracting the value of the black hole spin from the direct high-resolution image of black hole by using a thin accretion disk model. In this model, the observed dark region on the first image of the supermassive black hole in the galaxy M87, obtained by the Event Horizon Telescope, is a silhouette of the black hole event horizon. The outline of this silhouette is the equator of the event horizon sphere. The dark silhouette of the black hole event horizon is placed within the expected position of the black hole shadow, which is not revealed on the first image. We calculated numerically the relation between the observed position of the black hole silhouette and the brightest point in the thin accretion disk, depending on the black hole spin. From this relation, we derive the spin of the supermassive black hole M87*, a = 0.75 ± 0.15 .

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.

OBSERVATIONAL CONSTRAINTS ON STRONG GRAVITY

2011 ◽  
Vol 20 (14) ◽  
pp. 2755-2760
Author(s):  
CHRIS DONE
Keyword(s):  
Black Hole ◽  
Event Horizon ◽  
Strong Field ◽  
Field Tests ◽  
High Energy ◽  
Observational Constraints ◽  
Tests Of General Relativity ◽  
Strong Gravity ◽  
Accretion Flows ◽  
Spacetime Curvature

Accretion onto a black hole transforms the darkest objects in the universe to the brightest. The high energy radiation emitted from the accretion flow before it disappears forever below the event horizon lights up the regions of strong spacetime curvature close to the black hole, enabling strong field tests of General Relativity. I review the observational constraints on strong gravity from such accretion flows, and show how the data strongly support the existence of such fundamental General Relativistic features of a last stable orbit and the event horizon. However, these successes also imply that gravity does not differ significantly from Einstein's predictions above the event horizon, so any new theory of quantum gravity will be very difficult to test.

Determination of supermassive black hole spins in active galactic nuclei

2020 ◽  
Vol 35 (02n03) ◽  
pp. 2040054
Author(s):  
M. Yu. Piotrovich ◽  
V. L. Afanasiev ◽  
S. D. Buliga ◽  
T. M. Natsvlishvili
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Active Galactic Nuclei ◽  
Accretion Disk ◽  
Galactic Nuclei ◽  
Supermassive Black Holes ◽  
Disk Model ◽  
Supermassive Black Hole

Based on spectropolarimetry for a number of active galactic nuclei in Seyfert 1 type galaxies observed with the 6-m BTA telescope, we have estimated the spins of the supermassive black holes at the centers of these galaxies. We have determined the spins based on the standard Shakura-Sunyaev accretion disk model. More than 70% of the investigated active galactic nuclei are shown to have Kerr supermassive black holes with a dimensionless spin greater than 0.9.

scholarly journals Probing the accretion disk - jet connection via instabilities in the inner accretion flow. From microquasars to quasars

2010 ◽  
Vol 6 (S275) ◽  
pp. 94-95
Author(s):  
Agnieszka Janiuk ◽  
Bożena Czerny ◽  
Monika Mościbrodzka ◽  
Aneta Siemiginowska
Keyword(s):  
Black Hole ◽  
Accretion Disk ◽  
Radiation Pressure ◽  
Duty Cycle ◽  
Thermal Instability ◽  
Accretion Flow ◽  
Supermassive Black Hole ◽  
Complex Morphology ◽  
Hydrogen Ionization ◽  
Jet Axis

AbstractWe present various instability mechanisms in the accreting black hole systems which might indicate at the connection between the accretion disk and jet. The jets observed in microquasars can have a peristent or blobby morphology. Correlated with the accretion luminosity, this might provide a link to the cyclic outbursts of the disk. Such duty-cycle type of behaviour on short timescales results from the thermal instability caused by the radiation pressure domination. The same type of instability may explain the cyclic radioactivity of the supermassive black hole systems. The somewhat longer timescales are characteristic for the instability caused by the partial hydrogen ionization. The distortions of the jet direction and complex morphology of the sources can be caused by precession of the disk-jet axis.

scholarly journals Low-frequency, one-armed oscillations in black hole accretion flows obtained from direct 3D MHD simulations

2006 ◽  
Vol 2 (S238) ◽  
pp. 405-406
Author(s):  
Mami Machida ◽  
Ryoji Matsumoto
Keyword(s):  
Black Hole ◽  
Low Frequency ◽  
Maximum Velocity ◽  
Relativistic Effects ◽  
Newtonian Potential ◽  
Opening Angle ◽  
Accretion Flows ◽  
Black Hole Accretion ◽  
Mhd Simulations ◽  
Hole Accretion

AbstractWe present the results of global 3D MHD simulations of optically thin black hole accretion flows. The initial disk is embedded in a low density, spherical, isothermal halo and threaded by weak (β ≡ Pgas/Pmag = 100) toroidal magnetic field. General relativistic effects are simulated by using the pseudo-Newtonian potential. When the Maxwell stress in the innermost region of the disk is reduced due to the loss of magnetic flux or by decrease of disk temperature, inner torus is created around 4 – 10rs. We found that in such an inner torus, one-armed (m = 1) density enhancement grows and that the inner torus oscillates quasi-periodically. The oscillation period is about 0.1s when we assume a 10M⊙ black hole. This frequency agrees with the low-frequency QPOs observed in low/hard state of black hole candidates. The disk ejects winds whose opening angle is about 30 degree. The maximum velocity of the wind is about 0.05c.

scholarly journals Black-Hole Accretion Corona Immersed in the Disk Radiation Fields

1998 ◽  
Vol 188 ◽  
pp. 419-420
Author(s):  
T. Miwa ◽  
Y. Watanabe ◽  
J. Fukue
Keyword(s):  
Black Hole ◽  
Pressure Gradient ◽  
Accretion Disk ◽  
Gradient Force ◽  
Pressure Gradient Force ◽  
Disk Model ◽  
Radiation Fields ◽  
Black Hole Accretion ◽  
Cold Case ◽  
Hole Accretion

We examined an accretion-disk corona around a black hole immersed in the disk radiation fields (cf. Watanabe, Fukue 1996a, b). The corona is supposed to be initially at rest far from the center. During infall above and below the disk, the corona is suffered from the disk radiation fields. As a disk model, we adopted the standard α-disk, and in order to mimic the general relativisitic effects, we use the pseudo-Newtonian force proposed by Artemova et al. (1996). Moreover, we assume that the corona is geometrically thin and optically thin, and ignored any motion such as wind. We consider the cold case, where the pressure-gradient force is ignored. Under these assumptions, we calculated the motion of the corona gas and found that the infall of corona is supressed due to disk radiation fields.

scholarly journals Observational constraints on angular momentum transfer during gravitational collapse*

1991 ◽  
Vol 147 ◽  
pp. 438-439
Author(s):  
Eric Keto
Keyword(s):  
Magnetic Field ◽  
Angular Momentum ◽  
Momentum Transfer ◽  
Accretion Disk ◽  
Rotation Curve ◽  
Simple Calculation ◽  
Observational Constraints ◽  
Molecular Line ◽  
Spectral Signatures ◽  
Accretion Flows

A simple calculation of the expected spectral signatures of model protostellar accretion flows suggests how the rotation curve of the accretion disk may be deduced from radio frequency molecular line observations. We compare synthetic observations with actual data to derive rotation curves, braking torques, and minimum magnetic field energies required to effect the braking.

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.

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