scholarly journals Einstein–Born–Infeld gravastar models, dark matter and accretion mechanisms

2019 ◽  
Vol 28 (08) ◽  
pp. 1950108 ◽  
Author(s):  
D. J. Cirilo-Lombardo ◽  
C. D. Vigh
Keyword(s):  
Momentum Tensor ◽  
Rate Of Change ◽  
Nonlinear Electrodynamics ◽  
Anisotropic Fluid ◽  
Spherically Symmetric ◽  
Regular Variety ◽  
Accretion Process ◽  
Accretion Rates ◽  
Exterior Regions ◽  
Spherically Symmetric Metric

Gravastar models have recently been proposed as an alternative to black holes, mainly to avoid the problematic issues associated with event horizons and singularities. In this work, a regular variety of gravastar models within the context of Einstein–Born–Infeld (EBI) nonlinear electrodynamics are builded. These models presented here are truly regular in the sense that both the metric and its derivatives are continuous throughout spacetime, contrary to other cases in the literature where matching conditions are necessary in the interior and exterior regions of the event horizon. We investigated the accretion process for spherically symmetric spacetime geometries generated for a nonlinear electromagnetic field where the energy–momentum tensor has the same form that an anisotropic fluid that is the general EBI case. We analyze this procedure using the most general static spherically symmetric metric ansatz. In this theoretical context, we examined the accretion process for specific spherically symmetric compact configuration obtaining the accretion rates and the accretion velocities during the process and the flow of the fluid around the black hole. In addition, we study the behavior of the rate of change of the mass for each chosen metric.

Five-dimensional spherical gravitational collapse of anisotropic fluid with cosmological constant

2017 ◽  
Vol 14 (02) ◽  
pp. 1750025 ◽  
Author(s):  
Suhail Khan ◽  
Hassan Shah ◽  
Ghulam Abbas
Keyword(s):  
Cosmological Constant ◽  
Apparent Horizon ◽  
Physical Significance ◽  
Anisotropic Fluid ◽  
Spherically Symmetric ◽  
Hole Size ◽  
Junction Conditions ◽  
De Sitter ◽  
Positive Cosmological Constant ◽  
Exterior Regions

Our aim is to study five-dimensional spherically symmetric anisotropic collapse with a positive cosmological constant (PCC). For this purpose, five-dimensional spherically symmetric and Schwarzschild–de Sitter metrics are chosen in the interior and exterior regions respectively. A set of junction conditions is derived for the smooth matching of interior and exterior spacetimes. The apparent horizon is calculated and its physical significance is studied. It comes out that the whole collapsing process is influenced by the cosmological constant. The collapsing process under the influence of cosmological constant slows down and black hole size also reduced.

MØLLER ENERGY–MOMENTUM COMPLEX FOR HIGHER-DIMENSIONAL SPHERICALLY SYMMETRIC SPACETIME IN GENERAL RELATIVITY

2012 ◽  
Vol 27 (40) ◽  
pp. 1250231 ◽  
Author(s):  
HÜSNÜ BAYSAL
Keyword(s):  
General Relativity ◽  
Momentum Density ◽  
Momentum Tensor ◽  
Symmetric Model ◽  
Spherically Symmetric ◽  
Higher Dimensional ◽  
Energy And Momentum ◽  
Momentum Complex ◽  
Spherically Symmetric Metric ◽  
Spherically Symmetric Model

We have calculated the total energy–momentum distribution associated with (n+2)-dimensional spherically symmetric model of the universe by using the Møller energy–momentum definition in general relativity (GR). We have found that components of Møller energy and momentum tensor for given spacetimes are different from zero. Also, we are able to get energy and momentum density of various well-known wormholes and black hole models by using the (n+2)-dimensional spherically symmetric metric. Also, our results have been discussed and compared with the results for four-dimensional spacetimes in literature.

Optical properties of Einstein–Born–Infeld gravastar models in plasmas

2020 ◽  
Vol 29 (12) ◽  
pp. 2050080
Author(s):  
D. J. Cirilo-Lombardo ◽  
L. S. Ridao
Keyword(s):  
Magnetized Plasma ◽  
Gravitational Lens ◽  
Nonlinear Electrodynamics ◽  
Nonlinear Field ◽  
Regular Variety ◽  
Total Delay ◽  
Event Horizons ◽  
Standard Linear ◽  
Exterior Regions ◽  
Optical Phenomena

Gravastar models have recently been proposed as an alternative to black holes, mainly to avoid the problematic issues associated with event horizons and singularities. Recently, in [D. J. Cirilo-Lombardo and C. D. Vigh, Int. J. Mod. Phys. D 28 (2019) 1950108], a regular variety of gravastar models within the context of Einstein–Born–Infeld (EBI) nonlinear electrodynamics were built. These original models are truly regular in the sense that both the metric and its derivatives are continuous throughout spacetime, contrary to other cases in the literature where matching conditions are necessary in the interior and exterior regions of the event horizon. In this work, in the same theoretical context from [D. J. Cirilo-Lombardo and C. D. Vigh, Int. J. Mod. Phys. D 28 (2019) 1950108], we study some optical phenomena, such as the weak gravitational lens for the case of the magnetized plasma and the influence of working with a nonlinear field of BI in observables such as the Einstein ring or the total delay time. These important issues allow us to compare the results obtained in the context of these new static Born–Infeld gravastars with the standard linear ones (e.g. Reissner–Nordström).

Spherically symmetric spacetime with radiating fluids in f(𝒢, T) gravity

2019 ◽  
Vol 34 (27) ◽  
pp. 1950215 ◽  
Author(s):  
M. Farasat Shamir ◽  
Nabeeha Uzair
Keyword(s):  
Weyl Tensor ◽  
Energy Momentum Tensor ◽  
Stellar System ◽  
Momentum Tensor ◽  
Anisotropic Fluid ◽  
Spherically Symmetric ◽  
Field Equations ◽  
Radiating Fluids ◽  
Inhomogeneity Factor ◽  
Symmetric Spacetime

The aim of this paper is to examine the irregularity factors of a self-gravitating stellar system in the existence of anisotropic fluid. We investigate the dynamics of field equations within [Formula: see text] background, where [Formula: see text] is the Gauss–Bonnet invariant and [Formula: see text] is the trace of the energy–momentum tensor. Moreover, we have investigated two differential equations using the conservation law and the Weyl tensor. We have determined the irregularity factors of spherical stellar system for some specific conditions of anisotropic and isotropic fluids, dust, radiating and non-radiating systems in [Formula: see text] gravity. It has been noted that the dissipative matter results in anisotropic stresses and makes the system more complex. The inhomogeneity factor is correlated to one of the scalar functions.

Spherically symmetric traversable wormholes in f(R2,T) gravity

2019 ◽  
Vol 16 (10) ◽  
pp. 1950147 ◽  
Author(s):  
M. Zubair ◽  
Quratulien Muneer ◽  
Saira Waheed
Keyword(s):  
Modified Gravity ◽  
Arbitrary Constant ◽  
Energy Momentum Tensor ◽  
Energy Condition ◽  
Momentum Tensor ◽  
Anisotropic Fluid ◽  
Spherically Symmetric ◽  
Matter Distribution ◽  
Field Equations ◽  
Traversable Wormholes

In this paper, we explore the possibility of wormhole solutions existence exhibiting spherical symmetry in an interesting modified gravity based on Ricci scalar term and trace of energy–momentum tensor. For this reason, we assume the matter distribution as anisotropic fluid and a specific viable form of the generic function given by [Formula: see text] involving [Formula: see text] and [Formula: see text], two arbitrary constant parameters. For having a simplified form of the resulting field equations, we assume three different forms of EoS of the assumed matter contents. In each case, we find the numerical wormhole solutions and analyze their properties for the wormhole existence graphically. The graphical behavior of the energy condition bounds is also investigated in each case. It is found that a realistic wormhole solutions satisfying all the properties can be obtained in each case.

Charged perfect fluid gravitational collapse in f(R, T) gravity

2019 ◽  
Vol 34 (20) ◽  
pp. 1950153 ◽  
Author(s):  
G. Abbas ◽  
Riaz Ahmed
Keyword(s):  
Perfect Fluid ◽  
Gravitational Collapse ◽  
Coupling Parameter ◽  
Apparent Horizon ◽  
Momentum Tensor ◽  
Spherically Symmetric ◽  
Einstein Field Equations ◽  
Field Equations ◽  
Apparent Horizons ◽  
Spherically Symmetric Metric

We explore the problem of charged perfect fluid spherically symmetric gravitational collapse in f(R, T) gravity (R is Ricci scalar and T is the trace of energy–momentum tensor). We have taken the interior boundary of a star as spherically symmetric metric filled with the charged perfect fluid. In order to study charged perfect fluid collapse, we have investigated the exact solutions of the Maxwell–Einstein field equations solutions using the most simplified form for f(R, T) model f(R, T) = R + 2[Formula: see text]T, where [Formula: see text] is model parameter. This study involves the effects of charge as well as coupling parameter on collapse of a star. We studied the nature of trapped surfaces, apparent horizon and singularity structure in detail. It has been found that singularity is formed earlier than the apparent horizons, so the end state of gravitational collapse in this case is black hole.

scholarly journals A Smarr formula for charged black holes in nonlinear electrodynamics

2017 ◽  
Vol 32 (39) ◽  
pp. 1750219 ◽  
Author(s):  
Leonardo Balart ◽  
Sharmanthie Fernando
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
General Formula ◽  
Energy Momentum Tensor ◽  
Momentum Tensor ◽  
Nonlinear Electrodynamics ◽  
Spherically Symmetric ◽  
Charged Black Holes ◽  
Electrically Charged ◽  
Black Hole Solutions

It is well known that the Smarr formula does not hold for black holes in nonlinear electrodynamics. The main reason for this is the fact that the trace of the energy–momentum tensor for nonlinear electrodynamics does not vanish as it is for Maxwell’s electrodynamics. Starting from the Komar integral, we derived a new Smarr-type formula for spherically symmetric static electrically charged black hole solutions in nonlinear electrodynamics. We show that this general formula is in agreement with some that are obtained for black hole solutions with nonlinear electrodynamics.

scholarly journals A Note on the Transformability of Spherically Symmetric Metrics

1953 ◽  
Vol 9 (1) ◽  
pp. 13-16 ◽  
Author(s):  
Paul Kustaanheimo
Keyword(s):  
Spherically Symmetric ◽  
Symmetric Metrics ◽  
Spherically Symmetric Metric

SummaryIt is shown that every spherically symmetric metric can be transformed into the isotropic form. As illustration an example is given.

scholarly journals The theory of spherically symmetric thin shells in conformal gravity

2018 ◽  
Vol 27 (06) ◽  
pp. 1841012 ◽  
Author(s):  
Victor Berezin ◽  
Vyacheslav Dokuchaev ◽  
Yury Eroshenko
Keyword(s):  
General Relativity ◽  
Weyl Tensor ◽  
Delta Function ◽  
Einstein Gravity ◽  
Riemann Tensor ◽  
Momentum Tensor ◽  
Thin Shells ◽  
Spherically Symmetric ◽  
Gravitational Fields ◽  
Gravitational Theories

The spherically symmetric thin shells are the nearest generalizations of the point-like particles. Moreover, they serve as the simple sources of the gravitational fields both in General Relativity and much more complex quadratic gravity theories. We are interested in the special and physically important case when all the quadratic in curvature tensor (Riemann tensor) and its contractions (Ricci tensor and scalar curvature) terms are present in the form of the square of Weyl tensor. By definition, the energy–momentum tensor of the thin shell is proportional to Diracs delta-function. We constructed the theory of the spherically symmetric thin shells for three types of gravitational theories with the shell: (1) General Relativity; (2) Pure conformal (Weyl) gravity where the gravitational part of the total Lagrangian is just the square of the Weyl tensor; (3) Weyl–Einstein gravity. The results are compared with these in General Relativity (Israel equations). We considered in detail the shells immersed in the vacuum. Some peculiar properties of such shells are found. In particular, for the traceless ([Formula: see text] massless) shell, it is shown that their dynamics cannot be derived from the matching conditions and, thus, is completely arbitrary. On the contrary, in the case of the Weyl–Einstein gravity, the trajectory of the same type of shell is completely restored even without knowledge of the outside solution.

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