Comment on “Can accretion disk properties observationally distinguish black holes from naked singularities?”

2018 ◽  
Vol 98 (8) ◽  
Author(s):  
Bertrand Chauvineau
Keyword(s):  
Black Holes ◽  
Accretion Disk ◽  
Naked Singularities

scholarly journals Image of the thin accretion disk around compact objects in the Einstein–Gauss–Bonnet gravity

2021 ◽  
Vol 81 (10) ◽  
Author(s):  
Galin Gyulchev ◽  
Petya Nedkova ◽  
Tsvetan Vetsov ◽  
Stoytcho Yazadjiev
Keyword(s):  
Black Holes ◽  
Accretion Disk ◽  
Physical Mechanism ◽  
Compact Object ◽  
Ring Structure ◽  
Compact Objects ◽  
Schwarzschild Black Hole ◽  
Naked Singularities ◽  
Bonnet Gravity ◽  
Light Ring

AbstractWe study the optical appearance of a thin accretion disk around compact objects within the Einstein–Gauss–Bonnet gravity. Considering static spherically symmetric black holes and naked singularities we search for characteristic signatures which can arise in the observable images due to the modification of general relativity. While the images of the Gauss–Bonnet black holes closely resemble the Schwarzschild black hole, naked singularities possess a distinctive feature. A series of bright rings are formed in the central part of the images with observable radiation $$10^3$$ 10 3 times larger than the rest of the flux making them observationally significant. We elucidate the physical mechanism, which causes the appearance of the central rings, showing that the image is determined by the light ring structure of the spacetime. In a certain region of the parametric space the Gauss–Bonnet naked singularities possess a stable and an unstable light ring. In addition the gravitational field becomes repulsive in a certain neighbourhood of the singularity. This combination of features leads to the formation of the central rings implying that the effect is not specific for the Einstein–Gauss–Bonnet gravity but would also appear for any other compact object with the same characteristics of the photon dynamics.

scholarly journals Observational signatures of strongly naked singularities: image of the thin accretion disk

2020 ◽  
Vol 80 (11) ◽  
Author(s):  
Galin Gyulchev ◽  
Jutta Kunz ◽  
Petya Nedkova ◽  
Tsvetan Vetsov ◽  
Stoytcho Yazadjiev
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Accretion Disk ◽  
Complex Structure ◽  
Ring Structure ◽  
Compact Objects ◽  
Naked Singularities ◽  
New Feature ◽  
Disk Image ◽  
Observational Signature

AbstractWe study the optical appearance of a thin accretion disk around the strongly naked static Janis–Newman–Winicour singularity. The solution does not possess a photon sphere, which results in the formation of a complex structure of bright rings in the central region of the disk image. Such structure is absent in the case of the Schwarzschild black hole with a thin accretion disk, where instead of the image we observe the black hole shadow. Some of the rings emit with the maximal observable radiation flux from the accretion disk, and should be experimentally detectable. Thus, this qualitatively new feature can be used to distinguish observationally black holes from naked singularities. We elucidate the appearance of the ring structure by revealing the physical mechanism of its formation, and explaining the nature of each of the ring images. We make the conjecture that a similar structure would also appear for other solutions without a photon sphere and it can serve as a general observational signature for distinguishing compact objects possessing no photon sphere from black holes.

scholarly journals HIGHER DIMENSIONAL INHOMOGENEOUS DUST COLLAPSE AND COSMIC CENSORSHIP

2002 ◽  
Vol 17 (20) ◽  
pp. 2747-2747
Author(s):  
A. BEESHAM
Keyword(s):  
Black Holes ◽  
Cosmic Censorship ◽  
De Sitter Spacetime ◽  
De Sitter ◽  
Naked Singularities ◽  
Singularity Theorems ◽  
Sitter Spacetime ◽  
Higher Dimensional ◽  
Cosmic Censorship Hypothesis ◽  
Strong Curvature

The singularity theorems of general relativity predict that gravitational collapse finally ends up in a spacetime singularity1. The cosmic censorship hypothesis (CCH) states that such a singularity is covered by an event horizon2. Despite much effort, there is no rigorous formulation or proof of the CCH. In view of this, examples that appear to violate the CCH and lead to naked singularities, in which non-spacelike curves can emerge, rather than black holes, are important to shed more light on the issue. We have studied several collapse scenarios which can lead to both situations3. In the case of the Vaidya-de Sitter spacetime4, we have shown that the naked singularities that arise are of the strong curvature type. Both types of singularities can also arise in higher dimensional Vaidya and Tolman-Bondi spacetimes, but black holes are favoured in some sense by the higher dimensions. The charged Vaidya-de Sitter spacetime also exhibits both types of singularities5.

scholarly journals Distinguishing black holes and naked singularities with iron line spectroscopy

2018 ◽  
Vol 2018 (08) ◽  
pp. 044-044 ◽  
Author(s):  
Honghui Liu ◽  
Menglei Zhou ◽  
Cosimo Bambi
Keyword(s):  
Black Holes ◽  
Iron Line ◽  
Naked Singularities

scholarly journals Launching proton-dominated jets from accreting Kerr Black Holes: the case of M87

2011 ◽  
Vol 1 (1) ◽  
pp. 4 ◽  
Author(s):  
Felix F. Brezinski ◽  
Ahmad A. Hujeirat
Keyword(s):  
Magnetic Field ◽  
Boundary Layer ◽  
Black Holes ◽  
Angular Momentum ◽  
Event Horizon ◽  
Accretion Disk ◽  
Lorentz Factor ◽  
Spin Parameter ◽  
Low Mass ◽  
Kerr Black Holes

A general relativistic model for the formation and acceleration of low mass-loaded jets from systems containing accreting black holes is presented. The model is based on previous numerical results and theoretical studies in the Newtonian regime, but modified to include the effects of space-time curvature in the vicinity of the event horizon of a spinning black hole. It is argued that the boundary layer between the Keplerian accretion disk and the event horizon is best suited for the formation and acceleration of the accretion-powered jets in active galactic nuclei and micro-quasars. The model presented here is based on matching the solutions of three different regions: i- a weakly magnetized Keplerian accretion disk in the outer part, where the transport of angular momentum is mediated through the magentorotational instability, ii- a strongly magnetized, advection-dominated and turbulent-free boundary layer (BL) between the outer cold accretion disk and the event horizon and where the plasma rotates sub-Keplerian and iii- a transition zone (TZ) between the BL and the overlying corona, where the electrons and protons are thermally uncoupled, highly dissipative and rotate super-Keplerian. In the BL, the gravitation-driven dynamical collapse of the plasma increases the strength of the poloidal magnetic field (PMF) significantly, subsequently suppressing the generation and dissipation of turbulence and turning off the primary source of heating. In this case, the BL appears much fainter than standard disk models so as if the disk truncates at a certain radius. The action of the PMF in the BL is to initiate torsional Alf`ven waves that transport angular momentum from the embedded plasma vertically into the TZ, where a significant fraction of the shear-generated toroidal magnetic field reconnects, thereby heating the protons up to the virial-temperature. Also, the strong PMF forces the electrons to cool rapidly, giving rise therefore to the formation of a gravitationally unbound two-temperature proton-dominated outflow. Our model predicts the known correlation between the Lorentz-factor and the spin parameter of the BH. It also shows that the effective surface of the BL, through which the baryons flow into the TZ, shrinks with increasing the spin parameter, implying therefore that low mass-loaded jets most likely originate from around Kerr black holes. When applying our model to the jet in the elliptical galaxy M87, we find a spin parameter <em>a ∈</em> [0.99, 0.998], a transition radius rtr ≈ 30 gravitational radii and a fraction of 0.05 − 0.1 of the mass accretion rate goes into the TZ, where the plasma speeds up its outward-oriented motion to reach a Lorentz factor Γ <em>∈</em> [2.5, 5.0] at rtr.

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 Hard-state Accretion Disk Winds from Black Holes: The Revealing Case of MAXI J1820+070

2019 ◽  
Vol 879 (1) ◽  
pp. L4 ◽  
Author(s):  
T. Muñoz-Darias ◽  
F. Jiménez-Ibarra ◽  
G. Panizo-Espinar ◽  
J. Casares ◽  
D. Mata Sánchez ◽  
...  
Keyword(s):  
Black Holes ◽  
Accretion Disk ◽  
Hard State
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