共查询到20条相似文献，搜索用时 0 毫秒
1.
We analyze spherical dust collapse with non-vanishing radial pressure, II, and vanishing tangential stresses. Considering a barotropic equation of state, II = , we obtain an analytical solution in closed form—which is exact for = –1, 0, and approximate otherwise—near the center of symmetry (where the curvature singularity forms). We study the formation, visibility, and curvature strength of singularities in the resulting spacetime. We find that visible, Tipler strong singularities can develop from generic initial data. Radial pressure alters the spectrum of possible endstates for collapse, increasing the parameter space region that contains no visible singularities, but cannot by itself prevent the formation of visible singularities for sufficiently low values of the energy density. Known results from pressureless dust are recovered in the = 0 limit. 相似文献
2.
Pankaj S Joshi 《Pramana》2000,55(4):529-544
An outstanding problem in gravitation theory and relativistic astrophysics today is to understand the final outcome of an
endless gravitational collapse. Such a continual collapse would take place when stars more massive than few times the mass
of the sun collapse under their own gravity on exhausting their nuclear fuel. According to the general theory of relativity,
this results either in a black hole, or a naked singularity — which can communicate with far away observers in the universe.
While black holes are (almost) being detected and are increasingly used to model high energy astrophysical phenomena, naked
singularities have turned into a topic of active discussion, aimed at understanding their structure and implications. Recent
developments here are reviewed, indicating future directions. 相似文献
3.
A Vaidya spacetime is considered for gravitational collapse of a type II fluid in the context of the Rastall theory of gravity. For a linear equation of state for the fluid profiles, the conditions under which the dynamical evolution of the collapse can give rise to the formation of a naked singularity are examined. It is shown that depending on the model parameters, strong curvature, naked singularities would arise as exact solutions to the Rastall's field equations. The allowed values of these parameters satisfy certain conditions on the physical reliability, nakedness, and the curvature strength of the singularity. It turns out that Rastall gravity, in comparison to general relativity, provides a wider class of physically reasonable spacetimes that admit both locally and globally naked singularities. 相似文献
4.
In this paper, we investigate the impact of the generalized uncertainty principle (GUP), proposed by some approaches to quantum gravity such as string theory and doubly special relativity theories (DSR), on black-hole physics. It turns out that such a modification will give corrections to both the temperature and the entropy of black holes. In particular, the proposed GUP also changes the picture of Hawking radiation greatly when the size of black holes approaches the Planck scale. It prevents black holes from total evaporation, predicting the existence of black-holes remnants which may be considered as a candidate for dark matter.https://doi.org/10.1209/0295-5075/100/20004 相似文献
5.
6.
F. A. Brito;F. F. Santos 《Europhysics letters》2020,129(5)
We investigate black brane solutions in asymptotically Lifshitz spacetime in -dimensional Horndeski gravity,which admit a critical exponent fixed at . The cosmological constant depends on z as . We compute the shear viscosity in the -dimensional dual boundary field theory via holographic correspondence. We investigate the violation of the bound for a viscosity to entropy density ratio of at .https://doi.org/10.1209/0295-5075/129/50003 相似文献
7.
Jafar Sadeghi Mehdi Shokri Mohammad Reza Alipour Saeed Noori Gashti 《中国物理C(英文版)》2023,47(1):015103-015103-9
We search for a possible relationship between weak gravity conjecture (WGC) and conformal field theory (CFT) in hyperscaling violating and Kerr-Newman-AdS black holes. We deal with the critical points of the black hole systems using the correlation function introduced in CFT and discuss WGC conditions using the imaginary part of the energy obtained from the critical points and their poles. Under the assumptions begin{document}$ z=1 $end{document} ![]()
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8.
Pieter-Jan De Smet 《General Relativity and Gravitation》2004,36(6):1501-1504
We point out that the Myers-Perry metric in five dimensions is algebraically special. It has Petrov type 22, which is the Petrov type of the five-dimensional Schwarzschild metric. 相似文献
9.
B S Sathyaprakash 《Pramana》2001,56(4):457-475
The new millennium will see the upcoming of several ground-based interferometric gravitational wave antennas. Within the next
decade a space-based antenna may also begin to observe the distant Universe. These gravitational wave detectors will together
operate as a network taking data continuously for several years, watching the transient and continuous phenomena occurring
in the deep cores of astronomical objects and dense environs of the early Universe where gravity was extremely strong and
highly nonlinear. The network will listen to the waves from rapidly spinning non-axisymmetric neutron stars, normal modes
of black holes, binary black hole inspiral and merger, phase transitions in the early Universe, quantum fluctuations resulting
in a characteristic background in the early Universe. The gravitational wave antennas will open a new window to observe the
dark Universe unreachable via other channels of astronomical observations. 相似文献
10.
C. Bambi 《Europhysics letters》2011,94(5)
Nowadays we believe that a typical galaxy contains about 107 stellar-mass black holes and a single super-massive black hole at its center. According to general relativity, these objects are characterized solely by their mass M and by their spin parameter a *. A fundamental limit for a black hole in general relativity is the Kerr bound |a *| ≤ 1, but the accretion process can spin it up to a * ≈ 0.998. If a compact object is not a black hole, the Kerr bound does not hold and in this letter I provide some evidences suggesting that the accretion process could spin the body up to a * > 1. While this fact should be negligible for stellar-mass objects, some of the super-massive objects at the center of galaxies may actually be super-spinning bodies exceeding the Kerr bound. Such a possibility can be tested by gravitational wave detectors like LISA or by sub-millimeter very long-baseline interferometry facilities.https://doi.org/10.1209/0295-5075/94/50002 相似文献
11.
We explore the quadratic form of the gravitational theory to derive rotating N-dimensions black hole solutions with rotation parameters. Here, R is the Ricci scalar and b is the dimensional parameter. We assumed that the N-dimensional spacetime is static and it has flat horizons with a zero curvature boundary. We investigated the physics of black holes by calculating the relations of physical quantities such as the horizon radius and mass. We also demonstrate that, in the four-dimensional case, the higher-order curvature does not contribute to the black hole, i.e., black hole does not depend on the dimensional parameter b, whereas, in the case of , it depends on parameter b, owing to the contribution of the correction term. We analyze the conserved quantities, energy, and angular-momentum, of black hole solutions by applying the relocalization method. Additionally, we calculate the thermodynamic quantities, such as temperature and entropy, and examine the stability of black hole solutions locally and show that they have thermodynamic stability. Moreover, the calculations of entropy put a constraint on the parameter b to be to obtain a positive entropy. 相似文献
12.
Following Rosen's quantization rules,two of the authors (C. Corda and F. Feleppa) recently described the Schwarzschild black hole (BH) formed after the gravitational collapse of a pressureless “star of dust” in terms of a “gravitational hydrogen atom”. Here we generalize this approach to the gravitational collapse of a charged object,namely,to the geometry of a Reissner-Nordström BH (RNBH) and calculate the gravitational potential,the Schrödinger equation and the exact solutions of the energy levels of the gravitational collapse. By using the concept of BH effective state ,previously introduced by one of us (CC),we describe the quantum gravitational potential,the mass spectrum and the energy spectrum for the extremal RNBH. The area spectrum derived from the mass spectrum finds agreement with a previous result by Bekenstein. The stability of these solutions,described with the Majorana approach to the Archaic Universe scenario,shows the existence of oscillatory regimes or exponential damping for the evolution of a small perturbation from a stable state.https://doi.org/10.1209/0295-5075/132/30001 相似文献
13.
Roberto Giambò Fabio Giannoni Giulio Magli Paolo Piccione 《General Relativity and Gravitation》2004,36(6):1279-1298
The gravitational collapse of spherical, barotropic perfect fluids is analyzed here. For the first time, the final state of these systems is studied without resorting to simplifying assumptions - such as self-similarity - using a new approach based on non-linear o.d.e. techniques, and formation of naked singularities is shown to occur for solutions such that the mass function is analytic in a neighborhood of the spacetime singularity. 相似文献
14.
Li Xiang;Yi Xie 《Europhysics letters》2021,133(4)
The tunneling probability of a Schwarzschild black hole is ill-defined,if the second-order WKB approximation is considered. In this letter,the second-order tunneling probability of a Bardeen black hole is carefully investigated,and it is found to be regularized by the magnetic charge q . When the black hole entropy is maintained to be non-negative and monotonic increasing,the magnetic charge is restricted by . The minimal probability refers to such a transition that the final state is a black hole remnant of Planck length.https://doi.org/10.1209/0295-5075/133/40005 相似文献
15.
We consider cosmological and black hole solutions in the Einstein and higher-derivative gravity in two dimensions where the theory is formulated first in D dimensions. In the limit that D tends to 2 with simultaneous singular rescaling of the scalar curvature coupling constant as ,we get the novel Einstein and higher-derivative gravity. Due to non-trivial contribution of scalar curvature which is topological invariant in exactly two dimensions to gravitational equations in the two-dimensional limit one gets novel cosmological and black hole solutions. In particular,the de Sitter and radiation-dominated universe and the Schwarzschild–de Sitter and Schwarzschild–anti-de Sitter black hole solutions are obtained and their properties are discussed.https://doi.org/10.1209/0295-5075/130/10004 相似文献
16.
Ivan Arraut 《Europhysics letters》2015,109(1)
I explain in a simple and compact form the origin of the apparent loss of predictability inside the de Rham-Gabadadze-Tolley (dRGT) non-linear formulation of massive gravity. This apparent pathology was first reported by Kodama and the author when the stability of the Schwarzschild-de Sitter (S-dS) black hole in dRGT was analyzed. If we study the motion of a massive test particle around the S-dS solution, we find that the total energy is not conserved in the usual sense. The conserved quantity associated with time appears as a combination of the total energy and a velocity-dependent term. If the equations of motion are written in terms of this conserved quantity, then the three-dimensional motion in dRGT will not differ with respect to the same situation of Einstein gravity (GR). The differences with respect to GR will appear whenever we have a dynamical situation. I explore the Hawking radiation as an example where we can find differences between GR and dRGT.https://doi.org/10.1209/0295-5075/109/10002 相似文献
17.
The accretion process is being investigated onto some important black holes such as Born-Infeld-AdS black hole, non-linear charged black hole solution in AdS space-time and Einstein-Yang-Mills massive gravity in the presence of Born-Infeld nonlinear electrodynamics. We find out the relations of radial velocity, energy density and change of mass for mention black holes and analyze their behavior graphically for different values of equation of state parameters $omega$. We also examine the relations for critical speed for these black holes. It is observed that for different state parameters different fluids exhibit different evolutions in black holes backgrounds. The energy density of some fluids is negative or positive near the black hole while other fluids become cause to increase or decrease in black hole mass. 相似文献
18.
Juan Wu;Wei Xu 《Europhysics letters》2019,125(6)
In this paper,we study entropy relations and bounds of regular and singular black holes with nonlinear electrodynamics sources. We focus on the regular and singular Bardeen and Hayward black holes in asymptotically flat and AdS spacetimes. For black holes with vanishing effective mass ,it is found that the entropy product is always mass-independent in asymptotically flat spacetime,while the entropy sum takes the mass-independent universality in asymptotically AdS spacetime. For the cases with nonzero effective mass in asymptotically flat and AdS spacetimes,entropy relations are both some functions of mass and charge,hence are always mass-dependent. Besides,the non-linear electrodynamics always affects the entropy bounds of horizons.https://doi.org/10.1209/0295-5075/125/60002 相似文献
19.
Jie-Xiong Mo 《Europhysics letters》2014,105(2)
In this letter, the original expressions of Erhenfest equations have been introduced directly into the black-hole research by treating the cosmological constant and its conjugate quantity as thermodynamic pressure and volume, respectively. The nature of phase transition at the critical point of criticality of AdS black holes in f (R ) gravity has been investigated as an example. The specific heat at constant pressure C P , the volume expansion coefficient α and the isothermal compressibility coefficient are found to diverge at the critical point. An analytical check of Ehrenfest equations has been carried out and it has been proved that both Ehrenfest equations are satisfied. So AdS black holes in f (R ) gravity undergo a second-order phase transition at the critical point. This result is consistent with the nature of liquid-gas phase transition at the critical point and would help deepen the understanding of the relations between AdS black holes and liquid-gas system. Moreover, the influences of f (R ) correction on the thermodynamics and the phase transition of AdS black holes in f (R ) gravity have also been shown in this letter.https://doi.org/10.1209/0295-5075/105/20003 相似文献
20.
R. Brustein 《Fortschritte der Physik》2014,62(3):255-265
It is argued that the blackhole information paradox originates from treating the blackhole geometry as strictly classical. It is further argued that the theory of quantum fields in a classical curved space with a horizon is an ill posed problem. If the geometry is allowed to fluctuate quantum mechanically, then the horizon effectively disappears. The sharp horizon emerges only in the classical limit when the ratio of the Compton wavelength of the black hole to its Schwarzschild radius vanishes. The region of strong gravity that develops when matter collapses to form the blackhole remains visible to the whole of spacetime and has to be described by a microscopic theory of strong gravity. The arguments imply that the information paradox is demoted from a paradox involving fundamental principles of physics to the problem of describing how matter at the highest densities gravitates. 相似文献