scholarly journals Gravitational entropy of wormholes with exotic matter and in galactic halos

2020 ◽  
Vol 29 (02) ◽  
pp. 2050015
Author(s):  
R. de C. Lima ◽  
José A. C. Nogales ◽  
S. H. Pereira
Keyword(s):  
Black Holes ◽  
Entropy Density ◽  
Exotic Matter ◽  
Galactic Halos ◽  
Maximum Flux ◽  
Gravitational Entropy ◽  
Nontrivial Topology

In this work, we study and compare the features of gravitational entropy near the throat of transversable wormholes formed by exotic matter and wormholes in galactic halos. We have verified that gravitational entropy and entropy density of these wormholes in regions near their throats are indistinguishable for objects of same throat, despite the fact that they are described by different metrics and by distinct energy–momentum tensors. We have found that the gravitational entropy density diverges near the throat for both cases, probably due to a nontrivial topology at this point, however, allowing the interesting interpretation that a maximum flux of information can be carried through the throat of these wormholes. In addition, we have found that both are endowed with an entropic behaviour similar to Hawking–Bekenstein’s entropy of nonrotating and null charge black holes.

scholarly journals On the gravitational entropy of accelerating black holes

2020 ◽  
Vol 29 (05) ◽  
pp. 2050034
Author(s):  
Sarbari Guha ◽  
Samarjit Chakraborty
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Phenomenological Approach ◽  
Entropy Density ◽  
Charged Black Hole ◽  
Einstein Field Equations ◽  
Field Equations ◽  
Gravitational Entropy ◽  
Definition Of ◽  
Black Hole Solutions

In this paper, we have examined the validity of a proposed definition of gravitational entropy in the context of accelerating black hole solutions of the Einstein field equations, which represent the realistic black hole solutions. We have adopted a phenomenological approach proposed in Rudjord et al. [Phys. Scr. 77, 055901 (2008)] and expanded by Romero et al. [Int. J. Theor. Phys. 51, 925 (2012)], in which the Weyl curvature hypothesis is tested against the expressions for the gravitational entropy. Considering the [Formula: see text]-metric for the accelerating black holes, we have evaluated the gravitational entropy and the corresponding entropy density for four different types of black holes, namely, nonrotating black hole, nonrotating charged black hole, rotating black hole and rotating charged black hole. We end up by discussing the merits of such an analysis and the possible reason of failure in the particular case of rotating charged black hole and comment on the possible resolution of the problem.

scholarly journals Causality of black holes in 4-dimensional Einstein–Gauss–Bonnet–Maxwell theory

2020 ◽  
Vol 80 (8) ◽  
Author(s):  
Xian-Hui Ge ◽  
Sang-Jin Sin
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Shear Viscosity ◽  
Upper Bound ◽  
Causal Structure ◽  
Density Ratio ◽  
Entropy Density ◽  
Coupling Constant ◽  
Maxwell Theory ◽  
Black Hole Solutions

Abstract We study charged black hole solutions in 4-dimensional (4D) Einstein–Gauss–Bonnet–Maxwell theory to the linearized perturbation level. We first compute the shear viscosity to entropy density ratio. We then demonstrate how bulk causal structure analysis imposes an upper bound on the Gauss–Bonnet coupling constant in the AdS space. Causality constrains the value of Gauss–Bonnet coupling constant $$\alpha _{GB}$$αGB to be bounded by $$\alpha _{GB}\le 0$$αGB≤0 as $$D\rightarrow 4$$D→4.

scholarly journals An exploration of the black hole entropy in Gauss–Bonnet gravity via the Weyl tensor

2021 ◽  
pp. 2150193
Author(s):  
Taha A. Malik ◽  
Rafael Lopez-Mobilia
Keyword(s):  
General Relativity ◽  
Black Hole ◽  
Weyl Tensor ◽  
Black Hole Entropy ◽  
Entropy Density ◽  
Modified Theories Of Gravity ◽  
Bonnet Gravity ◽  
Gravitational Entropy ◽  
Theories Of Gravity ◽  
Almost All

Various proposals for gravitational entropy densities have been constructed from the Weyl tensor. In almost all cases, though, these studies have been restricted to general relativity, and little has been done in modified theories of gravity. However, in this paper, we investigate the simplest proposal for an entropy density constructed from the Weyl tensor in five-dimensional Gauss–Bonnet gravity and find that it fails to reproduce the expected entropy of a black hole.

Gravitational lensing by black holes and their alternatives

2017 ◽  
Vol 26 (05) ◽  
pp. 1741013 ◽  
Author(s):  
Valerio Bozza
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Infinite Number ◽  
Gravitational Lensing ◽  
Exotic Matter ◽  
Asymptotic Limit ◽  
Light Rays ◽  
Alternative Solutions

Black holes have the ability to generate infinite number of images of any given source. These relativistic images are formed by light rays winding around the black hole several times. The phenomenology associated with these images is very rich, since these features are very sensitive to the metric structure of the black hole. Here, we review some aspects of gravitational lensing by black holes and consider some fundamental aspects related to alternative solutions, which do not reproduce Schwarzschild in the asymptotic limit and are supported by exotic matter.

Thin-shell wormhole from ABGB–de Sitter black holes

2021 ◽  
pp. 2150085
Author(s):  
Nilofar Rahman ◽  
Masum Murshid ◽  
Mehedi Kalam
Keyword(s):  
Black Holes ◽  
Surface Stress ◽  
Thin Shell ◽  
Exotic Matter ◽  
Linear Perturbation ◽  
De Sitter ◽  
Wormhole Solution ◽  
The Stability ◽  
De Sitter Universe ◽  
Charge Formula

A thin shell wormhole is constructed utilizing the cut and paste technique from ABGB–de Sitter black hole derived by Matyjasek et al. The surface stress localized at the wormhole throat is determined using Darmois–Israel formalism. We examine the attractive and repulsive nature of the thin shell wormhole on which cosmological constant [Formula: see text] has a significant effect. For the fixed values of charge [Formula: see text] and mass [Formula: see text], the attractiveness of the wormhole decreases with increasing [Formula: see text]. We calculate the total amount of exotic matter in the shell, which is not much affected by [Formula: see text]. For the construction of the wormhole in de Sitter universe, the regular black holes have to be heavily charged with a light mass to minimize the amount of required exotic matter. The stability of the wormhole solution is explored by considering a general equation of state in the form of linear perturbation. The stability regions are shown in the figures.

ENTROPY OF A ROTATING AND ARBITRARILY ACCELERATING BLACK HOLE

2003 ◽  
Vol 12 (06) ◽  
pp. 1083-1094 ◽  
Author(s):  
XUEJUN YANG ◽  
YIWEN HAN ◽  
ZHENG ZHAO
Keyword(s):  
Thin Film ◽  
Black Holes ◽  
Black Hole ◽  
Surface Area ◽  
Entropy Density ◽  
Brick Wall ◽  
Total Entropy ◽  
Wall Model ◽  
Brick Wall Model ◽  
Nonstationary Black Hole

The entropy of a rotating and arbitrarily accelerating black hole whose metric changes slowly is calculated using the thin film brick-wall model. We obtain the entropy density at every point of the horizon surface and the total entropy of the black hole. The results show that the entropy of the nonstationary black hole is also proportional to the surface area of the black hole's event horizon as in the cases of stationary black holes.

TOPOLOGICAL STRUCTURE OF ENTROPY OF (3+1)-DIMENSIONAL SPHERICALLY SYMMETRIC BLACK HOLES

2001 ◽  
Vol 16 (22) ◽  
pp. 1457-1464 ◽  
Author(s):  
GUO-HONG YANG
Keyword(s):  
Black Holes ◽  
Vector Field ◽  
Physical Meaning ◽  
Topological Structure ◽  
Killing Vector ◽  
Entropy Density ◽  
Topological Invariants ◽  
Spherically Symmetric ◽  
Killing Vector Field ◽  
The Relationship

Using the relationship between the entropy and the Euler characteristic, an entropy density is introduced to describe the inner topological structure of the entropy of (3+1)-dimensional spherically symmetric black holes. It is pointed out that the density of entropy is determined by the singularities of the timelike Killing vector field of space–time, and these singularities carry the topological numbers, Hopf indices and Brouwer degrees, naturally, which are topological invariants. Taking account of the physical meaning in statistics, the entropy of black holes is given by the Hopf indices merely, which will lead to the increasing principle of entropy of black holes.

scholarly journals On Regular Black Holes at Finite Temperature

2020 ◽  
Vol 2020 ◽  
pp. 1-9
Author(s):  
S. C. Ulhoa ◽  
E. P. Spaniol ◽  
R. Gomes ◽  
A. F. Santos ◽  
A. E. Santana
Keyword(s):  
Black Holes ◽  
General Relativity ◽  
Event Horizon ◽  
Finite Temperature ◽  
Casimir Effect ◽  
First Law Of Thermodynamics ◽  
Regular Black Holes ◽  
Thermo Field Dynamics ◽  
Gravitational Entropy ◽  
Boltzmann Law

The Thermo Field Dynamics (TFD) formalism is used to investigate the regular black holes at finite temperature. Using the Teleparalelism Equivalent to General Relativity (TEGR), the gravitational Stefan-Boltzmann law and the gravitational Casimir effect at zero and finite temperature are calculated. In addition, the first law of thermodynamics is considered. Then, the gravitational entropy and the temperature of the event horizon of a class of regular black holes are determined.

A theoretical construction of thin-shell wormhole from regular charged black holes

2020 ◽  
Vol 35 (23) ◽  
pp. 2050136
Author(s):  
Nilofar Rahman ◽  
Masum Murshid ◽  
Farook Rahaman ◽  
Mehedi Kalam
Keyword(s):  
Black Holes ◽  
Equation Of State ◽  
Thin Shell ◽  
Stability Region ◽  
Exotic Matter ◽  
Nonlinear Electrodynamics ◽  
Linear Perturbation ◽  
Charged Black Holes ◽  
Theoretical Construction ◽  
The Stability

We construct a thin-shell wormhole using the cut and paste technique from regular charged black holes with a nonlinear electrodynamics source (proposed by Balart and Vagenas). Using Darmois–Israel formalism we determine the surface stresses, which are localized at the wormhole throat. We also determine the amount of exotic matter present in the shell. To analyze the stability of the constructed wormhole we consider an equation of state as a linear perturbation. The stability region is shown in the graph by varying the values of the parameter.

scholarly journals Gravitational Entropy of Black Holes and Wormholes

2011 ◽  
Vol 51 (3) ◽  
pp. 925-942 ◽  
Author(s):  
Gustavo E. Romero ◽  
Romain Thomas ◽  
Daniela Pérez
Keyword(s):  
Black Holes ◽  
Gravitational Entropy
Sign in / Sign up

Export Citation Format

Share Document