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.

scholarly journals An Exact Model of an Anisotropic Relativistic Sphere

1995 ◽  
Vol 48 (4) ◽  
pp. 635 ◽  
Author(s):  
LK Patel ◽  
NP Mehta
Keyword(s):  
Exact Solution ◽  
General Relativity ◽  
Fluid Sphere ◽  
Anisotropic Fluid ◽  
Physical Parameters ◽  
Field Equations ◽  
Exterior Solution ◽  
Exact Model ◽  
Anisotropic Fluid Sphere

In this paper the field equations of general relativity are solved to obtain an exact solution for a static anisotropic fluid sphere. The solution is free from singularity and satisfies the necessary physical requirements. The physical 3-space of the solution is pseudo-spheroidal. The solution is matched at the boundary with the Schwarzschild exterior solution. Numerical estimates of various physical parameters are briefly discussed.

scholarly journals A new solution of embedding class I representing anisotropic fluid sphere in general relativity

2016 ◽  
Vol 25 (14) ◽  
pp. 1650099 ◽  
Author(s):  
Ksh. Newton Singh ◽  
Piyali Bhar ◽  
Neeraj Pant
Keyword(s):  
Graphical Representation ◽  
Compact Objects ◽  
Compact Stars ◽  
Anisotropic Fluid ◽  
Physical Parameters ◽  
Satisfactory Description ◽  
Anisotropic Fluid Sphere ◽  
Acceptable Model ◽  
Anisotropic Star ◽  
New Formula

In this paper, we are willing to develop a model of an anisotropic star by choosing a new [Formula: see text] metric potential. All the physical parameters like the matter density, radial and transverse pressure are regular inside the anisotropic star, with the speed of sound less than the speed of light. So the new solution obtained by us gives satisfactory description of realistic astrophysical compact stars. The model of this paper is compatible with observational data of compact objects like RX J1856-37, Her X-1, Vela X-12 and Cen X-3. A particular model of Her X-1 (Mass 0.98 [Formula: see text] and radius[Formula: see text]=[Formula: see text]6.7 km.) is studied in detail and found that it satisfies all the condition needed for physically acceptable model. Our model is described analytically as well as with the help of graphical representation.

scholarly journals Axially symmetric shear-free fluids in f(R,T) gravity

2017 ◽  
Vol 26 (11) ◽  
pp. 1750128 ◽  
Author(s):  
Ifra Noureen ◽  
M. Zubair
Keyword(s):  
Evolution Equation ◽  
Index Formula ◽  
Linear Perturbation ◽  
Physical Parameters ◽  
Axially Symmetric ◽  
Dynamical Equations ◽  
Free Condition ◽  
Instability Range ◽  
Metric Functions ◽  
Axial System

In this work, we have discussed the implications of shear-free condition on axially symmetric anisotropic gravitating objects in [Formula: see text] theory. Restricted axial symmetry ignoring rotation and reflection entries containing three independent metric functions is taken into account for establishment of instability range. Implementation of linear perturbation on constitutive modified dynamical equations yield evolution equation. This equation associates adiabatic index [Formula: see text] with material and dark source components of physical parameters defining stable and unstable regions in Newtonian (N) and post-Newtonian (pN) approximations. It is remarked that the axial system evolving under shear-free condition implicates high levels of stability in anisotropic environment.

Anisotropic strange quintessence stars in f(R,G) gravity

2020 ◽  
Vol 17 (14) ◽  
pp. 2050216
Author(s):  
M. Farasat Shamir ◽  
G. Mustafa ◽  
Mahroz Javed
Keyword(s):  
Compact Stars ◽  
Energy Conditions ◽  
Anisotropic Fluid ◽  
Physical Parameters ◽  
Dynamical Equations ◽  
Central Singularity ◽  
Compactness Factor ◽  
Celestial Bodies ◽  
Quintessence Field ◽  
Modified Formula

This paper is devoted to formulate a new model of quintessence anisotropic compact stars in the modified [Formula: see text] gravity. Dynamical equations in modified theory consisting of anisotropic fluid along with quintessence field have been evaluated by adopting analytical solution of Krori–Barua. In order to determine the unknown constraints of Krori–Barua metric observational data of different stars, [Formula: see text]-[Formula: see text], [Formula: see text], [Formula: see text]-[Formula: see text] has been taken into account. To solve the dynamical equations Starobinsky-like model, [Formula: see text] of modified gravity has been used. The outcome of the results depicts that all the examined celestial bodies are free from central singularity and are physically stable. Different physical parameters, such as energy density, energy conditions, evolution of quintessence and compactness factor, have been reviewed in detail.

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.

scholarly journals Supermassive black holes surrounded by dark matter modeled as anisotropic fluid: epicyclic oscillations and their fitting to observed QPOs

2021 ◽  
Vol 2021 (11) ◽  
pp. 059
Author(s):  
Z. Stuchlík ◽  
J. Vrba
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Dark Matter ◽  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
Supermassive Black Holes ◽  
Anisotropic Fluid ◽  
Physical Parameters ◽  
Black Hole Spacetimes ◽  
Test Particles

Abstract Recently introduced exact solution of the Einstein gravity coupled minimally to an anisotropic fluid representing dark matter can well represent supermassive black holes in galactic nuclei with realistic distribution of dark matter around the black hole, given by the Hernquist-like density distribution. For these fluid-hairy black hole spacetimes, properties of the gravitational radiation, quasinormal ringing, and optical phenomena were studied, giving interesting results. Here, using the range of physical parameters of these spacetimes allowing for their relevance in astrophysics, we study the epicyclic oscillatory motion of test particles in these spacetimes. The frequencies of the orbital and epicyclic motion are applied in the epicyclic resonance variant of the geodesic model of quasiperiodic oscillations (QPOs) observed in active galactic nuclei to demonstrate the possibility to solve the cases where the standard vacuum black hole spacetimes are not allowing for explanation of the observed data. We demonstrate that the geodesic model can explain the QPOs observed in most of the active galactic nuclei for the fluid-hairy black holes with reasonable halo parameters.

scholarly journals Mimicking static anisotropic fluid spheres in general relativity

2016 ◽  
Vol 25 (02) ◽  
pp. 1650019 ◽  
Author(s):  
Petarpa Boonserm ◽  
Tritos Ngampitipan ◽  
Matt Visser
Keyword(s):  
Electromagnetic Field ◽  
Scalar Field ◽  
Charge Density ◽  
Perfect Fluid ◽  
Radial Pressure ◽  
Energy Conditions ◽  
Fluid Sphere ◽  
Anisotropic Fluid ◽  
Spherically Symmetric ◽  
Anisotropic Fluid Sphere

We argue that an arbitrary general relativistic static anisotropic fluid sphere, (static and spherically symmetric but with transverse pressure not equal to radial pressure), can nevertheless be successfully mimicked by suitable linear combinations of theoretically attractive and quite simple classical matter: a classical (charged) isotropic perfect fluid, a classical electromagnetic field and a classical (minimally coupled) scalar field. While the most general decomposition is not unique, a preferred minimal decomposition can be constructed that is unique. We show how the classical energy conditions for the anisotropic fluid sphere can be related to energy conditions for the isotropic perfect fluid, electromagnetic field, and scalar field components of the model. Furthermore, we show how this decomposition relates to the distribution of both electric charge density and scalar charge density throughout the model. The generalized TOV equation implies that the perfect fluid component in this model is automatically in internal equilibrium, with pressure forces, electric forces, and scalar forces balancing the gravitational pseudo-force. Consequently, we can build theoretically attractive matter models that can be used to mimic almost any static spherically symmetric spacetime.

Embedded class solutions of an anisotropic object in Rastall gravity

2020 ◽  
Vol 35 (21) ◽  
pp. 2050109
Author(s):  
G. Mustafa ◽  
Tie-Cheng Xia
Keyword(s):  
Current Model ◽  
Compact Model ◽  
Physical Parameters ◽  
Equilibrium Stability ◽  
Field Equations ◽  
Energy Bounds ◽  
Extended Field ◽  
Metric Functions ◽  
Metric Function ◽  
Tov Equation

In this current work, we explore an anisotropic compact model with radius 9.1 km and mass 2.01 [Formula: see text] in the regime of Karmarkar condition in Rastall theory. To solve the extended field equations for the Rastall framework we have employed the Karmarkar condition. We investigate a comparative discussion to show the physical acceptance of Karmarkar condition in Rastall theory. Our obtained solutions, i.e. metric functions, density function and both the pressure components have well-behaved nature. The energy bounds and the equilibrium stability in the background of modified TOV equation (for Rastall proposal) are also discussed in this study. The parameter [Formula: see text] from [Formula: see text] metric function has some important role in this current model. All the calculated properties have different natures for [Formula: see text] to [Formula: see text]. In this current study we also discuss some physical parameters of this current model to check the validity of the model. In the end, it is concluded that our model is acceptable physically and geometrically.

scholarly journals Bianchi type-V cosmology with magnetized anisotropic dark energy

2017 ◽  
Vol 95 (3) ◽  
pp. 274-282
Author(s):  
M. Farasat Shamir ◽  
Asad Ali
Keyword(s):  
Magnetic Field ◽  
Dark Energy ◽  
Bianchi Type ◽  
Anisotropic Fluid ◽  
Physical Parameters ◽  
Anisotropic Universe ◽  
Field Equations ◽  
Constant Deceleration Parameter ◽  
Type V ◽  
Bianchi Type V

We study anisotropic universe in the presence of magnetized dark energy. Bianchi type-V cosmological model is considered for this purpose. The energy–momentum tensor consists of anisotropic fluid with uniform magnetic field of energy density ρB. Exact solutions to the field equations are obtained without using conventional assumptions like constant deceleration parameter. In particular, a general solution is obtained that further provides different classes of solutions. Only three cases have been discussed for the present analysis: linear, quadratic, and exponential. Graphical analyses of the solutions are done for all the three classes. The behavior of the model using some important physical parameters is discussed in the presence of magnetic field.

EXACT MODELS FOR ANISOTROPIC RELATIVISTIC STARS

2002 ◽  
Vol 11 (02) ◽  
pp. 207-221 ◽  
Author(s):  
M. K. MAK ◽  
PETER N. DOBSON ◽  
T. HARKO
Keyword(s):  
Energy Density ◽  
Density Ratio ◽  
Anisotropy Parameter ◽  
Integral Form ◽  
Radial Pressure ◽  
Physical Parameters ◽  
Field Equations ◽  
Gravitational Field Equations ◽  
Anisotropic Star ◽  
Decreasing Functions

We present a class of exact solutions of the Einstein gravitational field equations describing spherically symmetric and static anisotropic stellar type configurations. The solution is represented in a closed integral form. The energy density and both radial and tangential pressure are finite and positive inside the anisotropic star. The energy density, radial pressure, pressure-density ratio and the adiabatic speed of sound are monotonically decreasing functions. Several stellar models with the anisotropy coefficient proportional to r2 are discussed, the values of the basic physical parameters of the star (radius, mass and red shift) and bound on anisotropy parameter is obtained.

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