scholarly journals Testing cosmic censorship conjecture near extremal black holes with cosmological constants

2014 ◽  
Vol 23 (05) ◽  
pp. 1450044 ◽  
Author(s):  
Yuan Zhang ◽  
Sijie Gao
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Test Particle ◽  
Kerr Black Hole ◽  
Radiation Reaction ◽  
Cosmic Censorship ◽  
De Sitter ◽  
Test Particles ◽  
Cosmological Constants ◽  
Cosmic Censorship Conjecture

It has been shown previously that an extremal Reissner–Nordström or an extremal Kerr black hole cannot be overcharged or overspun by a test particle, if radiative and self-force effects are neglected. In this paper, we consider extremal charged and rotating black holes with cosmological constants. By studying the motion of test particles, we find the following results: An extremal Reissner–Nordström anti-de Sitter (RN–AdS) black hole can be overcharged by a test particle but an extremal Reissner–Nordström de Sitter (RN–dS) black hole cannot be overcharged. We also show that both extremal Kerr–de Sitter (Kerr–dS) and Kerr–anti-de Sitter (Kerr–AdS) black holes can be overspun by a test particle, implying a possible breakdown of the cosmic censorship conjecture. For the Kerr–AdS case, the overspinning requires that the energy of the particle be negative, a reminiscent of the Penrose process. In contrast to the extremal RN and Kerr black holes, in which cases the cosmic censorship is upheld, our results suggest some subtle relations between the cosmological constants and the cosmic censorship. We also discuss the effect of radiation reaction for the Kerr–dS case and find that the magnitude of energy loss due to gravitational radiation may not be enough to prevent the violation of the cosmic censorship.

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 A proof of the strong cosmic censorship conjecture

2020 ◽  
Vol 29 (14) ◽  
pp. 2042003
Author(s):  
Shahar Hod
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Second Law Of Thermodynamics ◽  
Cosmic Censorship ◽  
Necessary Condition ◽  
Deterministic Theory ◽  
Black Hole Spacetimes ◽  
Generalized Second Law ◽  
Strong Cosmic Censorship ◽  
Cosmic Censorship Conjecture

The Penrose strong cosmic censorship conjecture asserts that Cauchy horizons inside dynamically formed black holes are unstable to remnant matter fields that fall into the black holes. The physical importance of this conjecture stems from the fact that it provides a necessary condition for general relativity to be a truly deterministic theory of gravity. Determining the fate of the Penrose conjecture in nonasymptotically flat black hole spacetimes has been the focus of intense research efforts in recent years. In this paper, we provide a remarkably compact proof, which is based on Bekenstein’s generalized second law of thermodynamics, for the validity of the intriguing Penrose conjecture in physically realistic (dynamically formed) curved black hole spacetimes.

scholarly journals Strong cosmic censorship under quasinormal modes of non-minimally coupled massive scalar field

2019 ◽  
Vol 79 (9) ◽  
Author(s):  
Bogeun Gwak
Keyword(s):  
Black Holes ◽  
Scalar Field ◽  
Decay Rate ◽  
Small Mass ◽  
Cosmic Censorship ◽  
Massive Scalar ◽  
De Sitter ◽  
Massive Scalar Field ◽  
Strong Cosmic Censorship ◽  
Cosmic Censorship Conjecture

Abstract We investigate the strong cosmic censorship conjecture in lukewarm Reissner–Nordström–de Sitter black holes (and Martínez–Troncoso–Zanelli black holes) using the quasinormal resonance of non-minimally coupled massive scalar field. The strong cosmic censorship conjecture is closely related to the stability of the Cauchy horizon governed by the decay rate of the dominant quasinormal mode. Here, dominant modes are obtained in the limits of small and large mass black holes. Then, we connect the modes by using the WKB approximation. In our analysis, the strong cosmic censorship conjecture is valid except in the range of the small-mass limit, in which the dominant mode can be assumed to be that of the de Sitter spacetime. Particularly, the coupling constant and mass of the scalar field determine the decay rate in the small mass range. Therefore, the validity of the strong cosmic censorship conjecture depends on the characteristics of the scalar field.

scholarly journals Weak cosmic censorship conjecture in Kerr black holes of modified gravity

2019 ◽  
Vol 34 (05) ◽  
pp. 1950037 ◽  
Author(s):  
Bin Liang ◽  
Shao-Wen Wei ◽  
Yu-Xiao Liu
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Lower Energy ◽  
Energy Gap ◽  
Naked Singularity ◽  
Cosmic Censorship ◽  
Point Particle ◽  
Adiabatic Process ◽  
Energy Bounds ◽  
Cosmic Censorship Conjecture

By neglecting the effects of self-force and radiation, we investigate the possibility of destroying the Kerr-MOG black hole through the point particle absorption process. Using the instability of event horizon and equation of particle motion, we get the upper and lower energy bounds allowed for a matter particle to produce the naked singularity. We find that the energy gap always exists between the upper and lower energy bounds for both extremal and near-extremal black holes, which means some tailored particles can actually lead to the violation of the weak cosmic censorship conjecture. However, when considering the effect of the adiabatic process, the result shows that the Kerr-MOG black hole gets more stable instead of a naked singularity, and thus the weak cosmic censorship conjecture can be restored at some level.

scholarly journals Regular Bardeen Black Holes in Anti-de Sitter Spacetime versus Kerr Black Holes through Particle Dynamics

Galaxies ◽  
2021 ◽  
Vol 9 (3) ◽  
pp. 63
Author(s):  
Bakhtiyor Narzilloev ◽  
Javlon Rayimbaev ◽  
Ahmadjon Abdujabbarov ◽  
Bobomurat Ahmedov
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Magnetic Charge ◽  
Particle Dynamics ◽  
Kerr Metric ◽  
De Sitter Spacetime ◽  
De Sitter ◽  
Sitter Spacetime ◽  
Test Particles ◽  
Charge Parameter

In this work, test particle dynamics around a static regular Bardeen black hole (BH) in Anti-de Sitter spacetime has been studied. It has been shown for neutral test particles that parameters of a regular Bardeen black hole in Anti-de Sitter spacetime can mimic the rotation parameter of the Kerr metric up to the value a≈0.9 providing the same innermost stable circular orbit (ISCO) radius. We have also explored the dynamics of magnetized particles with a magnetic dipole moment around a magnetically charged regular Bardeen black hole in Anti-de Sitter spacetime. As a realistic astrophysical scenario of the study, we have treated neutron stars orbiting a supermassive black hole (SMBH), in particular, the magnetar PSR J1745-2900 orbiting Sgr A* with the parameter β=10.2, as magnetized test particles. The magnetized particles dynamics shows that the parameter β, negative values of cosmological constant and magnetic charge parameter of the central BH cause a decrease in the ISCO radius. We have compared the effects of the magnetic charge of the Bardeen BH with the spin of rotating Kerr BH and shown that magnetic charge parameter can mimic the spin in the range a/M≃(0,0.7896) when Λ=0 at the range of its values g/M≃(0,0.648).

scholarly journals Testing the weak cosmic censorship conjecture for a Reissner–Nordström–de Sitter black hole surrounded by perfect fluid dark matter

2021 ◽  
Vol 81 (7) ◽  
Author(s):  
Sanjar Shaymatov ◽  
Bobomurat Ahmedov ◽  
Mubasher Jamil
Keyword(s):  
Black Hole ◽  
Dark Matter ◽  
Cosmological Constant ◽  
Perfect Fluid ◽  
Linear Order ◽  
Cosmic Censorship ◽  
Cosmological Parameter ◽  
De Sitter ◽  
Non Linear ◽  
Cosmic Censorship Conjecture

AbstractIn this paper, we test the weak cosmic censorship conjecture (WCCC) for the Reissner–Nordström–de Sitter (RN-dS) black hole surrounded by perfect fluid dark matter. We consider a spherically symmetric perturbation on deriving linear and non-linear order perturbation inequalities by applying a new version of gedanken experiments well accepted from the work of Sorce and Wald. Contrary to the well-known result that the Reissner–Nordström (RN) black hole could be overcharged under linear order particle accretion it is hereby shown that the same black hole in perfect fluid dark matter with cosmological parameter cannot be overcharged. Considering a realistic scenario in which black holes cannot be considered to be in vacuum we investigate the contribution of dark matter and cosmological constant in the overcharging process of an electrically charged black hole. We demonstrate that the black hole can be overcharged only when two fields induced by dark matter and cosmological parameter are completely balanced. Further we present a remarkable result that a black hole cannot be overcharged beyond a certain threshold limit for which the effect arising from the cosmological constant dominates over the effect by the perfect fluid dark matter. Thus even for a linear accretion process, the black hole cannot always be overcharged and hence obeys the WCCC in general. This result would continue to be fulfilled for non-linear order accretion.

scholarly journals Exotic orbits due to spin–spin coupling around Kerr black holes

2017 ◽  
Vol 27 (01) ◽  
pp. 1750179 ◽  
Author(s):  
Wen-Biao Han ◽  
Shu-Cheng Yang
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Equatorial Plane ◽  
Strong Field ◽  
Kerr Black Hole ◽  
Spin Coupling ◽  
Spinning Particles ◽  
Test Particles ◽  
Kerr Black Holes ◽  
Large Spins

We report exotic orbital phenomena of spinning test particles orbiting around a Kerr black hole, i.e. some orbits of spinning particles are asymmetrical about the equatorial plane. When a nonspinning test particle orbits around a Kerr black hole in a strong field region, due to relativistic orbital precessions, the pattern of trajectories is symmetrical about the equatorial plane of the Kerr black hole. However, the patterns of the spinning particles’ orbit are no longer symmetrical about the equatorial plane for some orbital configurations and large spins. We argue that these asymmetrical patterns come from the spin–spin interactions between spinning particles and Kerr black holes, because the directions of spin–spin forces can be arbitrary, and distribute asymmetrically about the equatorial plane.

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