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.

Cracking in anisotropic polytropic models

2018 ◽  
Vol 33 (24) ◽  
pp. 1850139
Author(s):  
M. Sharif ◽  
Sobia Sadiq
Keyword(s):  
Distribution Function ◽  
Equation Of State ◽  
Anisotropic Fluid ◽  
Polytropic Index ◽  
Force Distribution ◽  
Spherically Symmetric ◽  
Field Equations ◽  
Polytropic Equation ◽  
Density Perturbations ◽  
Fluid Configuration

This paper is devoted to examine the cracking of spherically symmetric anisotropic fluid configuration for polytropic equation of state. For this purpose, we formulate the corresponding field equations as well as generalized Tolman–Oppenheimer–Volkoff equation. We introduce density perturbations in matter variables and then construct the force distribution function. In order to examine the occurrence of cracking/overturning, we consider two models corresponding to two values of the polytropic index. It is found that the first model exhibits overturning for the considered values of polytropic constant while the second model neither exhibits cracking nor overturning for larger values of polytropic constant.

Existence of dynamical wormholes in f(R) gravity

2020 ◽  
Vol 98 (5) ◽  
pp. 474-483
Author(s):  
Z. Yousaf ◽  
A. Ikram ◽  
M. Ilyas ◽  
M.Z. Bhatti
Keyword(s):  
Graphical Analysis ◽  
Energy Conditions ◽  
Anisotropic Fluid ◽  
Shape Functions ◽  
Field Equations ◽  
Ordinary Matter ◽  
Traversable Wormhole ◽  
Traversable Wormholes ◽  
Fluid Configuration

This paper explores spherically symmetrical dynamical traversable wormhole solutions for an anisotropic fluid configuration in the context of f(R) gravity. We construct the corresponding field equations and investigate the wormhole solutions by specifying the redshift and shape functions for three models of f(R) gravity. Graphical analysis shows that ordinary matter satisfies the null as well as weak energy conditions against the time and radial coordinates for each model. It is concluded that dynamical traversable wormholes are supported by this theory.

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 Study of generalized cylindrical polytropes with complexity factor

2021 ◽  
Vol 81 (9) ◽  
Author(s):  
Shiraz Khan ◽  
S. A. Mardan ◽  
M. A. Rehman
Keyword(s):  
Equation Of State ◽  
Energy Density ◽  
Differential Equations ◽  
Mass Density ◽  
Modify Form ◽  
Graphical Analysis ◽  
Fluid Distribution ◽  
Anisotropic Fluid ◽  
Polytropic Equation ◽  
Frame Work

AbstractIn this paper, complexity factor is used with generalized polytropic equation of state to develop two consistent systems of three differential equations and a general frame work is established for modify form of Lane-Emden equations. For this purpose anisotropic fluid distribution is considered in cylindrical static symmetry with two cases of generalized polytropic equation of state (i) mass density $$\mu _{o}$$ μ o and (ii) energy density $$\mu $$ μ . A graphical analysis will be carried out for the numerical solution of these systems of three differential equations.

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 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 Dark Energy Stars with Quadratic Equation of State

2019 ◽  
Author(s):  
Manuel Malaver ◽  
Hamed Kasmaei
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Energy Condition ◽  
Scalar Fields ◽  
Quadratic Equation ◽  
Accelerated Expansion ◽  
Fluid Distribution ◽  
Anisotropic Fluid ◽  
Field Equations ◽  
Quadratic Equation Of State

Recent astronomical observations with respect to measurements in distant supernovas, cosmic microwave background and weak gravitational lensing confirm that the Universe is undergoing a phase of accelerated expansion and it has been proposed that this cosmological behavior is caused by a hypothetical dark energy which has a strong negative pressure that allows explain the expanding universe. Several theoretical ideas and models related dark the energy includes the cosmological constant, quintessence, Chaplygin gas, braneworld and tachyonic scalar fields. In this paper, we have obtained new relativistic stellar configurations considering an anisotropic fluid distribution with a charge distribution which could represents a potential model of a dark energy star. In order to investigate the effect of a quadratic equation of state in this anisotropic model we specify particular forms for the gravitational potential that allow solving the Einstein-Maxwell field equations. For these new solutions we checked that the radial pressure, metric coefficients, energy density, anisotropy factor, charge density , mass function are well defined and are regular in the interior of the star. The solutions found can be used in the development of dark energy stars models satisfying all physical acceptability conditions but the causality condition and strong energy condition are violated. We expect that these models have multiple applications in astrophysics and cosmology.

scholarly journals Cosmological aspects of sound speed parameterizations in fractal universe

2019 ◽  
Vol 79 (11) ◽  
Author(s):  
Abdul Jawad ◽  
Sadaf Butt ◽  
Shamaila Rani ◽  
Khadija Asif
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Speed Of Sound ◽  
Cosmological Parameters ◽  
State Parameter ◽  
Graphical Analysis ◽  
Eos Parameter ◽  
Energy Models ◽  
Equation Of State Parameter ◽  
The Universe

AbstractIn the framework of fractal universe, the unified models of dark energy and dark matter are being presented with the background of homogenous and isotropic FLRW geometry. The aspects of fractal cosmology helps in better understanding of the universe in different dimensions. Relationship between the squared speed of the sound and the equation of state parameter is the key feature of these models. We have used constant as well as variable forms of speed of sound and express it as a function of equation of state parameter. By utilizing the four different forms of speed of sound, we construct the energy densities and pressures for these models and then various cosmological parameters like hubble parameter, EoS parameter, deceleration parameter and Om- diagnostic are investigated. Graphical analysis of these parameters show that in most of the cases EoS parameters and trajectories of Om-diagnostic corresponds to the quintessence like nature of the universe and the deceleration parameters represent accelerated and decelerated phase. In the end, we remark that cosmological analysis of these models indicates that these models correspond to different well known dark energy models.

scholarly journals Barotropic fluid compatible parametrizations of dark energy

2020 ◽  
Vol 80 (7) ◽  
Author(s):  
Dalibor Perković ◽  
Hrvoje Štefančić
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Speed Of Sound ◽  
Functional Form ◽  
State Parameter ◽  
Model Parameters ◽  
Barotropic Fluid ◽  
Energy Models ◽  
Equation Of State Parameter ◽  
Fundamental Requirement

Abstract Parametrizations of equation of state parameter as a function of the scale factor or redshift are frequently used in dark energy modeling. The question investigated in this paper is if parametrizations proposed in the literature are compatible with the dark energy being a barotropic fluid. The test of this compatibility is based on the functional form of the speed of sound squared, which for barotropic fluid dark energy follows directly from the function for the Equation of state parameter. The requirement that the speed of sound squared should be between 0 and speed of light squared provides constraints on model parameters using analytical and numerical methods. It is found that this fundamental requirement eliminates a large number of parametrizations as barotropic fluid dark energy models and puts strong constraints on parameters of other dark energy parametrizations.

DARK ENERGY WITH POLYTROPIC EQUATION-OF-STATE

2008 ◽  
Vol 23 (37) ◽  
pp. 3187-3198 ◽  
Author(s):  
UTPAL MUKHOPADHYAY ◽  
SAIBAL RAY ◽  
S. B. DUTTA CHOUDHURY
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Closed Form ◽  
State Parameter ◽  
Phantom Energy ◽  
Polytropic Index ◽  
Closed Form Solutions ◽  
Real Nature ◽  
Equation Of State Parameter ◽  
Polytropic Equation

Equation-of-state parameter plays a significant role for guessing the real nature of dark energy. Here polytropic equation-of-state p = ωρnis chosen for some of the kinematical Λ-models viz., [Formula: see text], [Formula: see text] and Λ ~ ρ. Although in dust cases (ω = 0) closed form solutions show no dependency on the polytropic index n, but in non-dust situations some new possibilities are opened up including phantom energy with supernegative (ω < -1) equation-of-state parameter.

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