Instability analysis of expansion-free sphere in f(𝒢) gravity

2017 ◽  
Vol 26 (09) ◽  
pp. 1750104
Author(s):  
M. Sharif ◽  
Ayesha Ikram
Keyword(s):  
Dynamical Instability ◽  
Anisotropic Fluid ◽  
Free Fluid ◽  
Perturbation Scheme ◽  
Field Equations ◽  
Dynamical Equations ◽  
First Order ◽  
Text Model ◽  
Metric Functions ◽  
Anisotropic Pressures

The aim of this paper is to study the dynamical instability of expansion-free spherically symmetric anisotropic fluid in the framework of [Formula: see text] gravity. We apply perturbation scheme of the first-order to the metric functions as well as matter variables and construct modified field equations for both static and perturbed configurations using power-law [Formula: see text] model. To discuss the instability dynamics, we use the contracted Bianchi identities to formulate the dynamical equations in both Newtonian and post-Newtonian regimes. It is found that the range of instability is independent of adiabatic index for expansion-free fluid but depends on anisotropic pressures, energy density and Gauss–Bonnet (GB) terms.

Anisotropic stellar filaments evolving under expansion-free condition in f(R,T) gravity

2018 ◽  
Vol 27 (04) ◽  
pp. 1850047 ◽  
Author(s):  
M. Zubair ◽  
Hina Azmat ◽  
Ifra Noureen
Keyword(s):  
Momentum Tensor ◽  
Index Formula ◽  
Dynamical Instability ◽  
Perturbation Scheme ◽  
Field Equations ◽  
Free Condition ◽  
Cylindrically Symmetric ◽  
Expansion Condition ◽  
Text Model

In this paper, we have analyzed the role of a viable [Formula: see text] model, i.e. [Formula: see text], while exploring the unstable regions of cylindrically symmetric gravitational source, where, [Formula: see text] and [Formula: see text] correspond to the Ricci invariant and trace of energy momentum tensor, respectively. The matter distribution is considered to be anisotropic and gravitating system evolves under zero expansion condition. The collapse equation of cylindrical star has been obtained by applying perturbation scheme on modified field equations and conservation equations. Dynamical instability has been discussed in N and pN regimes, stability constraints have also been developed. We found that adiabatic index [Formula: see text] is meaningless for the discussion of stability of gravitating sources carrying expansion-free condition, and stability variations are determined by physical properties of the fluid.

Impact of f(R,T) gravity in evolution of charged viscous fluids

2021 ◽  
Vol 30 (04) ◽  
pp. 2150027
Author(s):  
I. Noureen ◽  
Usman-ul-Haq ◽  
S. A. Mardan
Keyword(s):  
Stability Analysis ◽  
Energy Momentum Tensor ◽  
Momentum Tensor ◽  
Viscous Fluids ◽  
Fluid Distribution ◽  
Perturbation Scheme ◽  
Field Equations ◽  
Dynamical Equations ◽  
Stability Of Stars ◽  
The Stability

In this work, the evolution of spherically symmetric charged anisotropic viscous fluids is discussed in framework of [Formula: see text] gravity. In order to conduct the analysis, modified Einstein Maxwell field equations are constructed. Nonzero divergence of modified energy momentum tensor is taken that implicates dynamical equations. The perturbation scheme is applied to dynamical equations for stability analysis. The stability analysis is carried out in Newtonian and post-Newtonian limits. It is observed that charge, fluid distribution, electromagnetic field, viscosity and mass of the celestial objects greatly affect the collapsing process as well as stability of stars.

scholarly journals Modelling of a compact anisotropic star as an anisotropic fluid sphere in f(T) gravity

2018 ◽  
Vol 96 (12) ◽  
pp. 1295-1303 ◽  
Author(s):  
D. Momeni ◽  
G. Abbas ◽  
S. Qaisar ◽  
Zaid Zaz ◽  
R. Myrzakulov
Keyword(s):  
Anisotropic Fluid ◽  
Physical Parameters ◽  
Parametric Form ◽  
Dynamical Equations ◽  
Strange Stars ◽  
Exact Model ◽  
Anisotropic Fluid Sphere ◽  
Metric Functions ◽  
Anisotropic Stars ◽  
Anisotropic Star

In this article, the authors have discussed a new exact model of anisotropic stars in the f(T) theory of gravity. A parametric form of the metric functions has been implemented to solve the dynamical equations in f(T) theory with the anisotropic fluid. The novelty of the work is that the obtained solutions do not contain singularity but are potentially stable. The estimated values for mass and radius of the different strange stars, RX J 1856–37, Her X-1, and Vela X-12, have been utilized to find the values of unknown constants in Krori and Barua metrics. The physical parameters like anisotropy, stability, and redshift of the stars have been examined in detail.

Electromagnetic effects on the stability of anisotropic cylinder

2020 ◽  
Vol 35 (15) ◽  
pp. 2050124
Author(s):  
M. Sharif ◽  
Qanitah Ama-Tul-Mughani
Keyword(s):  
Radial Pressure ◽  
Baryon Number ◽  
Dynamical Instability ◽  
Perturbation Scheme ◽  
Dynamical Equations ◽  
Anisotropic Cylinder ◽  
Cylindrically Symmetric ◽  
Radial Perturbation ◽  
The Stability ◽  
Gaseous Star

This paper is devoted to analyzing the stability of charged anisotropic cylinder using the radial perturbation scheme. For this purpose, we consider the non-static cylindrically symmetric self-gravitating system and apply both Eulerian as well as Lagrangian approaches to establish a linearized perturbed form of dynamical equations. The conservation of baryon number is used to evaluate perturbed radial pressure in terms of an adiabatic index. A variational principle is developed to find a characteristic frequency which helps to examine the combined effect of charge and anisotropy on the stability of gaseous star. It is found that dynamical instability can be prevented until the radius of cylinder exceeds the limit [Formula: see text] and anisotropy increases the instability up to the limiting value of [Formula: see text]. Finally, we conclude that the system becomes more stable by increasing the definite amount of charge gradually.

scholarly journals f(T) Corrected Instability of Cylindrical Collapsing Object with Harrison-Wheeler Equation of State

2018 ◽  
Vol 2018 ◽  
pp. 1-11 ◽  
Author(s):  
Abdul Jawad ◽  
M. Azam
Keyword(s):  
Heat Conduction ◽  
Equation Of State ◽  
Teleparallel Gravity ◽  
Dynamical Instability ◽  
Heat Conducting ◽  
Matter Distribution ◽  
First Order ◽  
Cylindrical Object ◽  
Isotropic Pressure ◽  
Metric Functions

We study the dynamical instability of a collapsing object in the framework of generalized teleparallel gravity. We assume a cylindrical object with a specific matter distribution. This distribution contains energy density and isotropic pressure component with heat conduction. We take oscillating states scheme up to first order to check the instable behavior of the object. We construct a general collapse equation for underlying case with nondiagonal tetrad depending on the matter, metric functions, heat conducting term, and torsional terms. The Harrison-Wheeler equation of state which contains adiabatic index is used to explore the dynamical instability ranges for Newtonian and post-Newtonian constraints. These ranges depend on perturbed part of metric coefficients, matter parts, and torsion.

Dynamics of shearing viscous fluids in f(R,T) gravity

2017 ◽  
Vol 27 (01) ◽  
pp. 1750181 ◽  
Author(s):  
Hina Azmat ◽  
M. Zubair ◽  
Ifra Noureen
Keyword(s):  
Cylindrical Symmetry ◽  
Dynamical Analysis ◽  
Index Formula ◽  
Anisotropic Fluid ◽  
Perturbation Approach ◽  
Field Equations ◽  
Dynamical Equations ◽  
Cylindrical System ◽  
Pressure Anisotropy ◽  
The Stability

In this paper, we have analyzed the dynamical stability of shearing viscous anisotropic fluid with cylindrical symmetry in [Formula: see text] theory. We have chosen two viable [Formula: see text] models for dynamical analysis, and explored their nature and role for stable stellar configuration. Modified field equations and corresponding dynamical equations have been constructed, perturbation approach is adopted to deal with complexity of these equations. With the help of perturbed dynamical equations, the evolution equation has been established to analyze the role of shear viscosity and pressure anisotropy on dynamics of cylindrical system. The adiabatic index [Formula: see text] is used to investigate the instabilities appearing in Newtonian (N) and post-Newtonian (pN) approximations. Some conditions are found for material variables that are required to meet the stability criterion. We compare the outcomes of our analysis with the results of various models available in literature to reach at more comprehensive conclusion.

Dynamical variables and evolution of the universe

2017 ◽  
Vol 26 (04) ◽  
pp. 1750029 ◽  
Author(s):  
M. Zaeem-ul-Haq Bhatti ◽  
Z. Yousaf
Keyword(s):  
Dust Cloud ◽  
Charged Dust ◽  
Matter Distribution ◽  
Field Equations ◽  
Riemann Curvature Tensor ◽  
Dynamical Equations ◽  
Curvature Invariants ◽  
Imperfect Fluid ◽  
Text Model ◽  
The Universe

One of the striking feature of inhomogeneous matter distribution under the effects of fourth-order gravity and electromagnetic field have been discussed in this manuscript. We have considered a compact spherical celestial star undergoing expansion due to the presence of higher curvature invariants of [Formula: see text] gravity and imperfect fluid. We have explored the dynamical equations and field equations in [Formula: see text] gravity. An explicit expression have been found for Weyl tensor and material variables under the dark dynamical effects. Using a viable [Formula: see text] model, some dynamical variables have been explored from splitting the Riemann curvature tensor. These dark dynamical variables are also studied for charged dust cloud with and without the constraint of constant Ricci scalar.

scholarly journals Models of Anisotropic Self-Gravitating Source in Einstein-Gauss-Bonnet Gravity

2018 ◽  
Vol 2018 ◽  
pp. 1-12 ◽  
Author(s):  
G. Abbas ◽  
M. Tahir
Keyword(s):  
Surface Condition ◽  
Energy Conditions ◽  
Anisotropic Fluid ◽  
Field Equations ◽  
Spherical Source ◽  
Bonnet Gravity ◽  
Trapped Surface ◽  
Metric Functions ◽  
Definition Of ◽  
Metric Function

In this paper, we have studied gravitational collapse and expansion of nonstatic anisotropic fluid in 5D Einstein-Gauss-Bonnet gravity. For this purpose, the field equations have been modeled and evaluated for the given source and geometry. The two metric functions have been expressed in terms of parametric form of third metric function. We have examined the range of parameter β (appearing in the form of metric functions) for which Θ, the expansion scalar, becoming positive/negative leads to expansion/collapse of the source. The trapped surface condition has been explored by using definition of Misner-Sharp mass and auxiliary solutions. The auxiliary solutions of the field equations involve a single function that generates two types of anisotropic solutions. Each solution can be represented in term of arbitrary function of time; this function has been chosen arbitrarily to fit the different astrophysical time profiles. The existing solutions forecast gravitational expansion and collapse depending on the choice of initial data. In this case, wall to wall collapse of spherical source has been investigated. The dynamics of the spherical source have been observed graphically with the effects of Gauss-Bonnet coupling term α in the case of collapse and expansion. The energy conditions are satisfied for the specific values of parameters in both solutions; this implies that the solutions are physically acceptable.

scholarly journals Dissipative cylindrical collapse of a charged anisotropic fluid in f(R) gravity

2017 ◽  
Vol 95 (12) ◽  
pp. 1278-1284
Author(s):  
M. Farasat Shamir ◽  
M. Atif Fayyaz
Keyword(s):  
General Relativity ◽  
Heat Flow ◽  
Field Strength ◽  
Anisotropic Fluid ◽  
Perturbation Scheme ◽  
Dynamical Equations ◽  
Curvature Term ◽  
Physical Variables ◽  
Limiting Case ◽  
Cylindrical Collapse

This paper is devoted to investigating the cylindrical collapse of an anisotropic fluid in f(R) gravity. For this purpose, the viscous charged anisotropic fluid dissipating energy with heat flow and shear is assumed. We use the perturbation scheme to develop the dynamical equations for the variables that ultimately lead to the disturbance of the physical variables and the Starobinksy-like f(R) model chosen. The evolution of the matter variables is discussed with the help of these equations. It can be concluded that the range of dynamic instabilities depends on the field strength, density distribution, pressure, and the curvature term of the f(R) model. We find that our results of Newtonian and post-Newtonian regimes reduce asymptotically to general relativity solutions in the limiting case.

scholarly journals Cylindrically Symmetric, Asymptotically Flat, Petrov Type D Spacetime with a Naked Curvature Singularity and Matter Collapse

2017 ◽  
Vol 2017 ◽  
pp. 1-6 ◽  
Author(s):  
Faizuddin Ahmed
Keyword(s):  
Cosmic Time ◽  
Petrov Type ◽  
Energy Conditions ◽  
Anisotropic Fluid ◽  
Curvature Singularity ◽  
Field Equations ◽  
Asymptotically Flat ◽  
Type D ◽  
Cylindrically Symmetric ◽  
Petrov Type D

We present a cylindrically symmetric, Petrov type D, nonexpanding, shear-free, and vorticity-free solution of Einstein’s field equations. The spacetime is asymptotically flat radially and regular everywhere except on the symmetry axis where it possesses a naked curvature singularity. The energy-momentum tensor of the spacetime is that for an anisotropic fluid which satisfies the different energy conditions. This spacetime is used to generate a rotating spacetime which admits closed timelike curves and may represent a Cosmic Time Machine.

Sign in / Sign up

Export Citation Format

Share Document