THE DANGERS OF EXTREMES

2010 ◽  
Vol 19 (14) ◽  
pp. 2417-2422
Author(s):  
DONALD MAROLF
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Mechanical Model ◽  
Quantum Mechanical ◽  
Back Reaction ◽  
Extreme Black Hole ◽  
Test Particles ◽  
The Moment ◽  
Extreme Black Holes ◽  
Interior Solutions

While extreme black hole space–times with smooth horizons are known at the level of mathematics, we argue that the horizons of physical extreme black holes are effectively singular. Test particles encounter a singularity the moment they cross the horizon, and only objects with significant back-reaction can fall across a smooth (now non-extreme) horizon. As a result, classical interior solutions for extreme black holes are theoretical fictions that need not be reproduced by any quantum mechanical model. This observation suggests that significant quantum effects might be visible outside extreme or nearly extreme black holes. It also suggests that the microphysics of such black holes may be very different from that of their Schwarzschild cousins.

scholarly journals EXTREME BLACK HOLE ENTROPY OBTAINED IN AN OPERATIONAL APPROACH

2001 ◽  
Vol 16 (08) ◽  
pp. 1367-1375 ◽  
Author(s):  
BIN WANG ◽  
RU-KENG SU ◽  
ELCIO ABDALLA
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Black Hole Entropy ◽  
De Sitter ◽  
Operational Approach ◽  
Extreme Black Hole ◽  
The Stability ◽  
Extreme Black Holes

The entropy of anti-de Sitter Reissner–Nordström black hole is found to be stored in the material which gathers to form it and equals to A/4 regardless of material states. Extending the study to two kinds of extreme black holes, we find different entropy results for the first kind of extreme black hole due to different material states. However for the second kind of extreme black hole the results of entropy are uniform independently of the material states. Relations between these results and the stability of two kinds of extreme black holes have been addressed.

CAN THREE-DIMENSIONAL EXTREME BLACK HOLES DEVELOP FROM THEIR NONEXTREME COUNTERPARTS?

1999 ◽  
Vol 14 (20) ◽  
pp. 1329-1334
Author(s):  
BIN WANG ◽  
ELCIO ABDALLA ◽  
RU-KENG SU
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Angular Momentum ◽  
Three Dimensional ◽  
Rotating Black Hole ◽  
Test Particles ◽  
Extreme Black Holes

By applying the gedanken experiments, we have proved that the three-dimensional nonextreme charged and rotating black hole cannot become extreme by absorbing test particles to increase their charge and angular momentum.

scholarly journals Supermassive black holes surrounded by dark matter modeled as anisotropic fluid: epicyclic oscillations and their fitting to observed QPOs

2021 ◽  
Vol 2021 (11) ◽  
pp. 059
Author(s):  
Z. Stuchlík ◽  
J. Vrba
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Dark Matter ◽  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
Supermassive Black Holes ◽  
Anisotropic Fluid ◽  
Physical Parameters ◽  
Black Hole Spacetimes ◽  
Test Particles

Abstract Recently introduced exact solution of the Einstein gravity coupled minimally to an anisotropic fluid representing dark matter can well represent supermassive black holes in galactic nuclei with realistic distribution of dark matter around the black hole, given by the Hernquist-like density distribution. For these fluid-hairy black hole spacetimes, properties of the gravitational radiation, quasinormal ringing, and optical phenomena were studied, giving interesting results. Here, using the range of physical parameters of these spacetimes allowing for their relevance in astrophysics, we study the epicyclic oscillatory motion of test particles in these spacetimes. The frequencies of the orbital and epicyclic motion are applied in the epicyclic resonance variant of the geodesic model of quasiperiodic oscillations (QPOs) observed in active galactic nuclei to demonstrate the possibility to solve the cases where the standard vacuum black hole spacetimes are not allowing for explanation of the observed data. We demonstrate that the geodesic model can explain the QPOs observed in most of the active galactic nuclei for the fluid-hairy black holes with reasonable halo parameters.

scholarly journals Self-Regular Black Holes Quantized by means of an Analogue to Hydrogen Atoms

2016 ◽  
Vol 2016 ◽  
pp. 1-7 ◽  
Author(s):  
Chang Liu ◽  
Yan-Gang Miao ◽  
Yu-Mei Wu ◽  
Yu-Hao Zhang
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Mass Density ◽  
Hydrogen Atoms ◽  
Quantum Black Hole ◽  
Extreme Black Hole ◽  
Angular Momenta ◽  
Probability Densities ◽  
Hoop Conjecture ◽  
Hole Model

We suggest a quantum black hole model that is based on an analogue to hydrogen atoms. A self-regular Schwarzschild-AdS black hole is investigated, where the mass density of the extreme black hole is given by the probability density of the ground state of hydrogen atoms and the mass densities of nonextreme black holes are given by the probability densities of excited states with no angular momenta. Such an analogue is inclined to adopt quantization of black hole horizons. In this way, the total mass of black holes is quantized. Furthermore, the quantum hoop conjecture and the Correspondence Principle are discussed.

The effect of dark matter on the weak cosmic censorship conjecture in the extended space

2021 ◽  
pp. 2150207
Author(s):  
Zi-Yu Fu ◽  
Bao-Qi Zhang ◽  
Chuan-Yin Wang ◽  
Hui-Ling Li
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Dark Matter ◽  
Second Law Of Thermodynamics ◽  
Cosmic Censorship ◽  
De Sitter ◽  
Extended Phase ◽  
Extended Space ◽  
Extreme Black Holes ◽  
Cosmic Censorship Conjecture

By analyzing the energy–momentum relationship of the absorbed fermions dropping into a Reissner–Nordstöm–anti-de Sitter black hole surrounded by dark matter, the laws of thermodynamic and weak cosmic censorship conjecture in the extended phase space are investigated. We find that the first law of thermodynamics is valid. However, the validity of the second law of thermodynamics depends on the density [Formula: see text] of the perfect fluid dark matter. In addition, we also find that when the fermions are absorbed, the structures of black hole surrounded by dark matter would not change. Therefore, weak cosmic censorship conjecture holds for the extreme black holes and the non-extreme black holes.

Bound orbits around modified Hayward black holes

2021 ◽  
Author(s):  
Bo Gao ◽  
Xue-Mei Deng
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Angular Momentum ◽  
Gravitational Field ◽  
Periodic Orbits ◽  
Kerr Black Hole ◽  
Periodic Oscillations ◽  
Test Particles ◽  
Spin Parameter ◽  
Bound Orbits

The neutral time-like particle’s bound orbits around modified Hayward black holes have been investigated. We find that both in the marginally bound orbits (MBO) and the innermost stable circular orbits (ISCO), the test particle’s radius and its angular momentum are all more sensitive to one of the parameters [Formula: see text]. Especially, modified Hayward black holes with [Formula: see text] could mimic the same ISCO radius around the Kerr black hole with the spin parameter up to [Formula: see text]. Small [Formula: see text] could mimic the ISCO of small-spinning test particles around Schwarzschild black holes. Meanwhile, rational (periodic) orbits around modified Hayward black holes have also been studied. The epicyclic frequencies of the quasi-circular motion around modified Hayward black holes are calculated and discussed with respect to the observed Quasi-periodic oscillations (QPOs) frequencies. Our results show that rational orbits around modified Hayward black holes have different values of the energy from the ones of Schwarzschild black holes. The epicyclic frequencies in modified Hayward black holes have different frequencies from Schwarzschild and Kerr ones. These might provide hints for distinguishing modified Hayward black holes from Schwarzschild and Kerr ones by using the dynamics of time-like particles around the strong gravitational field.

scholarly journals External energy paradigm for black holes

2018 ◽  
Vol 33 (31) ◽  
pp. 1844025 ◽  
Author(s):  
Yuan K. Ha
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Gravitational Energy ◽  
Electrostatic Energy ◽  
New Paradigm ◽  
External Energy ◽  
Quantum Particles ◽  
Remarkable Result ◽  
The Moment ◽  
Constituent Mass

A new paradigm for black holes is introduced. It is known as the External Energy Paradigm. The paradigm asserts that all energies of a black hole are external quantities; they are absent inside the horizon. These energies include constituent mass, gravitational energy, electrostatic energy, rotational energy, heat energy, etc. As a result, quantum particles with charges and spins cannot exist inside the black hole. To validate the conclusion, we derive the moment of inertia of a Schwarzschild black hole and find that it is exactly equal to mass [Formula: see text] (Schwarzschild radius)2, indicating that all mass of the black hole is located at the horizon. This remarkable result can resolve several long-standing paradoxes in black hole theory; such as why entropy is proportional to area and not to volume, the singularity problem, the information loss problem and the perplexing firewall controversy.

Tunneling in Horava–Lifshitz black hole

2013 ◽  
Vol 91 (1) ◽  
pp. 64-70 ◽  
Author(s):  
J. Sadeghi ◽  
A. Banijamali ◽  
E. Reisi
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Dimensional Space ◽  
Null Geodesic ◽  
Hawking Temperature ◽  
Jacobi Method ◽  
Back Reaction ◽  
Dimensional Space Time ◽  
Lifshitz Black Holes ◽  
Lifshitz Black Hole

In this paper, using the Hamilton–Jacobi method we first calculate the Hawking temperature for a Horava–Lifshitz black hole. Then by utilizing the radial null geodesic method we obtain the entropy of such a black hole in four-dimensional space–time. We also consider the effect of back reaction on the surface gravity and compute modifications of entropy and Hawking temperature because of such an effect. Our calculations are for two kinds of Horava–Lifshitz black holes: Kehagias–Sfetsos and Lu–Mei–Pope.

scholarly journals DISCUSSION ON SOME CHARACTERISTICS OF CHARGED BRANE-WORLD BLACK HOLES

2009 ◽  
Vol 24 (04) ◽  
pp. 719-739 ◽  
Author(s):  
M. KALAM ◽  
F. RAHAMAN ◽  
A. GHOSH ◽  
B. RAYCHAUDHURI
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Gravitational Field ◽  
Scalar Field ◽  
Brane World ◽  
Massless Scalar ◽  
Massless Scalar Field ◽  
Effective Potentials ◽  
Test Particles ◽  
Jacobi Formalism

Several physical natures of charged brane-world black holes are investigated. Firstly, the timelike and null geodesics of the charged brane-world black holes are presented. We also analyze all the possible motions by plotting the effective potentials for various parameters for circular and radial geodesics. Secondly, we investigate the motion of test particles in the gravitational field of the charged brane-world black holes using the Hamilton–Jacobi formalism. We consider charged and uncharged test particles and examine their behavior in both static and nonstatic cases. Thirdly, the thermodynamics of the charged brane-world black holes are studied. Finally, it is shown that there is no phenomenon of superradiance for an incident massless scalar field for such a black hole.

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