Study of stellar structures in f(R,T) gravity

2018 ◽  
Vol 27 (07) ◽  
pp. 1850065 ◽  
Author(s):  
M. Sharif ◽  
Aisha Siddiqa
Keyword(s):  
Equation Of State ◽  
Equilibrium Equation ◽  
Hydrostatic Equilibrium ◽  
Compact Objects ◽  
Energy Conditions ◽  
Model Parameters ◽  
Field Equations ◽  
Quark Stars ◽  
Mit Bag Model ◽  
Polytropic Equation

This paper is devoted to study the compact objects whose pressure and density are related through polytropic equation-of-state (EoS) and MIT bag model (for quark stars) in the background of [Formula: see text] gravity. We solve the field equations together with the hydrostatic equilibrium equation numerically for the model [Formula: see text] and discuss physical properties of the resulting solution. It is observed that for both types of stars (polytropic and quark stars), the effects of model parameters [Formula: see text] and [Formula: see text] remain the same. We also obtain that the energy conditions are satisfied and stellar configurations are stable for both EoS.

Study of some compact objects in R + 2βT gravity

2019 ◽  
Vol 28 (16) ◽  
pp. 2040005
Author(s):  
Arfa Waseem ◽  
M. Sharif
Keyword(s):  
Stellar System ◽  
Graphical Analysis ◽  
Compact Objects ◽  
Stellar Structure ◽  
Energy Conditions ◽  
Spherically Symmetric ◽  
Field Equations ◽  
Star Models ◽  
Mit Bag Model ◽  
Text Model

The aim of this work is to examine the nature as well as physical characteristics of anisotropic spherically symmetric stellar candidates in the context of [Formula: see text] gravity. We assume that the fluid components such as pressure and energy density are related through MIT bag model equation-of-state in the interior of stellar system. In order to analyze the structure formation of some specific star models, the field equations are constructed using Krori–Barua solution in which the unknown constants are evaluated by employing observed values of radii and masses of the considered stars. We check the consistency of [Formula: see text] model through the graphical analysis of energy conditions as well as stability of stellar structure. It is found that our considered stars show viable as well as stable behavior for this model.

scholarly journals Impact of generalized polytropic equation of state on charged anisotropic polytropes

2020 ◽  
Vol 80 (2) ◽  
Author(s):  
S. A. Mardan ◽  
M. Rehman ◽  
I. Noureen ◽  
R. N. Jamil
Keyword(s):  
Equation Of State ◽  
Speed Of Sound ◽  
Graphical Analysis ◽  
Maxwell Field ◽  
Anisotropic Fluid ◽  
Polytropic Index ◽  
Model Parameters ◽  
Field Equations ◽  
Polytropic Equation ◽  
Fluid Configuration

Abstract In this paper, generalized polytropic equation of state is used to get new classes of polytropic models from the solution of Einstein-Maxwell field equations for charged anisotropic fluid configuration. The models are developed for different values of polytropic index $$n=1,~\frac{1}{2},~2$$n=1,12,2. Masses and radii of eight different stars have been regained with the help of developed models. The speed of sound technique and graphical analysis of model parameters is used for the viability of developed models. The analysis of models indicates they are well behaved and physically viable.

scholarly journals Role of σR2 + γRμνTμν model on anisotropic polytropes

2018 ◽  
Vol 27 (16) ◽  
pp. 1950007
Author(s):  
M. Sharif ◽  
Arfa Waseem
Keyword(s):  
Energy Conditions ◽  
Model Parameters ◽  
Causality Condition ◽  
Field Equations ◽  
Tangential Pressure ◽  
Anisotropic Factor ◽  
Polytropic Equation ◽  
Chandrasekhar Limit ◽  
Surface Redshift

This paper analyzes the anisotropic stellar evolution governed by polytropic equation-of-state in the framework of [Formula: see text] gravity, where [Formula: see text]. We construct the field equations, hydrostatic equilibrium equation and trace equation to obtain their solutions numerically under the influence of [Formula: see text] gravity model, where [Formula: see text] and [Formula: see text] are arbitrary constants. We examine the dependence of various physical characteristics such as radial/tangential pressure, energy density, anisotropic factor, total mass and surface redshift for specific values of the model parameters. The physical acceptability of the considered model is discussed by verifying the validity of energy conditions, causality condition and adiabatic index. We also study the effects arising due to strong nonminimal matter-curvature coupling on anisotropic polytropes. It is found that the polytropic stars are stable and their maximum mass point lies within the required observational Chandrasekhar limit.

Gödel-type universe in f(R,G) gravity

2019 ◽  
Vol 16 (12) ◽  
pp. 1950188 ◽  
Author(s):  
M. Farasat Shamir ◽  
Saeeda Zia
Keyword(s):  
Equation Of State ◽  
Graphical Analysis ◽  
Gravity Models ◽  
Energy Conditions ◽  
Radial Coordinate ◽  
Model Parameters ◽  
Cylindrical Coordinates ◽  
Polytropic Equation ◽  
Expansion Of The Universe ◽  
The Universe

In the current study, we discuss Gödel-type universe in [Formula: see text] gravity. Analysis has been done by considering anisotropic and perfect fluid distributions. Energy conditions for two proposed [Formula: see text] gravity models have been studied for suitable values of model parameters. Furthermore, Tolman–Oppenheimer–Volkoff equation has been developed with cylindrical coordinates in [Formula: see text] gravity. The graphical analysis for both these models suggests that Tolman–Oppenheimer–Volkoff equation is obeyed in a specific interval for the radial coordinate [Formula: see text]. A polytropic equation of state has been discussed for two [Formula: see text] gravity models. By analyzing the energy conditions, it is concluded that Gödel-type universe with both [Formula: see text] gravity models supports the expansion of the universe for certain range of radial coordinates.

scholarly journals Mass-radius relation of compact objects

2019 ◽  
Vol 15 (S356) ◽  
pp. 383-384
Author(s):  
Seman Abaraya ◽  
Tolu Biressa
Keyword(s):  
Numerical Analysis ◽  
Equation Of State ◽  
Compact Objects ◽  
Mass Limit ◽  
Einstein Field Equations ◽  
Field Equations ◽  
Formation And Evolution ◽  
Active Research ◽  
Compact Sources ◽  
Astrophysical Research

AbstractCompact objects are of great interest in astrophysical research. There are active research interests in understanding better various aspects of formation and evolution of these objects. In this paper we addressed some problems related to the compact objects mass limit. We employed Einstein field equations (EFEs) to derive the equation of state (EoS). With the assumption of high densities and low temperature of compact sources, the derived equation of state is reduced to polytropic kind. Studying the polytropic equations we obtained similar physical implications, in agreement to previous works. Using the latest version of Mathematica-11 in our numerical analysis, we also obtained similar results except slight differences in accuracy.

scholarly journals Compact stars in f(ℛ,𝒢,𝒯 ) gravity

2021 ◽  
Vol 36 (24) ◽  
pp. 2150165
Author(s):  
M. Ilyas
Keyword(s):  
Test Particle ◽  
Gravitational Theory ◽  
Momentum Tensor ◽  
Conservation Equation ◽  
Compact Objects ◽  
Compact Stars ◽  
Energy Conditions ◽  
Field Equations ◽  
Physical Features ◽  
The Impact

This work is to introduce a new kind of modified gravitational theory, named as [Formula: see text] (also [Formula: see text]) gravity, where [Formula: see text] is the Ricci scalar, [Formula: see text] is Gauss–Bonnet invariant and [Formula: see text] is the trace of the energy–momentum tensor. With the help of different models in this gravity, we investigate some physical features of different relativistic compact stars. For this purpose, we develop the effectively modified field equations, conservation equation, and the equation of motion for test particle. Then, we check the impact of additional force (massive test particle followed by a nongeodesic line of geometry) on compact objects. Furthermore, we took three notable stars named as [Formula: see text], [Formula: see text] and [Formula: see text]. The physical behavior of the energy density, anisotropic pressures, different energy conditions, stability, anisotropy, and the equilibrium scenario of these strange compact stars are analyzed through various plots. Finally, we conclude that the energy conditions hold, and the core of these stars is so dense.

Stability of generalized polytropic models

2019 ◽  
Vol 16 (04) ◽  
pp. 1950056
Author(s):  
I. Nazir ◽  
M. Azam
Keyword(s):  
Equation Of State ◽  
Local Density ◽  
Hydrostatic Equilibrium ◽  
Physical Parameters ◽  
Spherically Symmetric ◽  
Anisotropic Matter ◽  
Polytropic Equation ◽  
Density Perturbations ◽  
Radial Forces ◽  
The Stability

In this paper, we have investigated the stability of a spherically symmetric object with charged anisotropic matter by using the concept of cracking. The cracking is a very intuitive technique to check the stability which is based on the analysis of the radial forces that appear on the system due to perturbations taking it out of its equilibrium state. For this, we have applied and studied the effect of local density perturbations to the hydrostatic equilibrium equation and on all the physical parameters with generalized polytropic equation of state. It is found that some of the generalized polytropic models exhibit cracking.

Study of tilted cylindrical quark star

2020 ◽  
Vol 35 (14) ◽  
pp. 2050110
Author(s):  
M. Sharif ◽  
Sumaira Nazir
Keyword(s):  
Numerical Solution ◽  
Energy Conditions ◽  
Fluid Distribution ◽  
Quark Star ◽  
Field Equations ◽  
Dynamical Equations ◽  
Stellar Matter ◽  
Mit Bag Model ◽  
Pressure Anisotropy ◽  
Physical Features

In this paper, we study perfect, anisotropic and anisotropic dissipative cylindrical quark star for the tilted observer. To this end, the field equations and dynamical equations are formulated and assume MIT bag model to find a numerical solution of the field equations. The behavior of resulting model is investigated by plotting density, pressure, anisotropy and energy conditions. We check viability of the solutions through physical features related to stellar matter configuration. Finally, we discuss stability for all the cases of fluid distribution.

Study of conformally flat polytropes with tilted congruence

2018 ◽  
Vol 27 (07) ◽  
pp. 1850063 ◽  
Author(s):  
M. Sharif ◽  
Sobia Sadiq
Keyword(s):  
Equation Of State ◽  
Matter Content ◽  
Energy Conditions ◽  
Spherically Symmetric ◽  
Conformally Flat ◽  
Flat Condition ◽  
Polytropic Equation ◽  
Dissipative Fluid ◽  
Symmetric Spacetime ◽  
Fluid Configuration

This paper is aimed to study the modeling of spherically symmetric spacetime in the presence of anisotropic dissipative fluid configuration. This is accomplished for an observer moving relative to matter content using two cases of polytropic equation-of-state under conformally flat condition. We formulate the corresponding generalized Tolman–Oppenheimer–Volkoff equation, mass equation, as well as energy conditions for both cases. The conformally flat condition is imposed to find an expression for anisotropy which helps to study spherically symmetric polytropes. Finally, Tolman mass is used to analyze stability of the resulting models.

scholarly journals An analytical anisotropic compact stellar model of embedding class I

2021 ◽  
Vol 36 (05) ◽  
pp. 2150028
Author(s):  
Lipi Baskey ◽  
Shyam Das ◽  
Farook Rahaman
Keyword(s):  
Radial Pressure ◽  
Stellar Model ◽  
Compact Objects ◽  
Compact Stars ◽  
Model Parameters ◽  
Field Equations ◽  
Principal Stresses ◽  
Schwarzschild Solution ◽  
Spherical Fluid ◽  
Physical Profile

A class of solutions of Einstein field equations satisfying Karmarkar embedding condition is presented which could describe static, spherical fluid configurations, and could serve as models for compact stars. The fluid under consideration has unequal principal stresses i.e. fluid is locally anisotropic. A certain physically motivated geometry of metric potential has been chosen and codependency of the metric potentials outlines the formation of the model. The exterior spacetime is assumed as described by the exterior Schwarzschild solution. The smooth matching of the interior to the exterior Schwarzschild spacetime metric across the boundary and the condition that radial pressure is zero across the boundary lead us to determine the model parameters. Physical requirements and stability analysis of the model demanded for a physically realistic star are satisfied. The developed model has been investigated graphically by exploring data from some of the known compact objects. The mass-radius (M-R) relationship that shows the maximum mass admissible for observed pulsars for a given surface density has also been investigated. Moreover, the physical profile of the moment of inertia (I) thus obtained from the solutions is confirmed by the Bejger–Haensel concept.

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