scholarly journals Model of Charged Anisotropic Strange Stars in Minimally Coupled f R Gravity

2021 ◽  
Vol 2021 ◽  
pp. 1-25
Author(s):  
H. Nazar ◽  
G. Abbas
Keyword(s):  
Energy Density ◽  
Graphical Representation ◽  
Radial Pressure ◽  
Mass Function ◽  
Compact Stars ◽  
Energy Conditions ◽  
Anisotropic Fluid ◽  
Field Equations ◽  
Strange Matter ◽  
New Family

In the present article, we have investigated a new family of nonsingular solutions of static relativistic compact sphere which incorporates the characteristics of anisotropic fluid and electromagnetic field in the context of minimally coupled f R theory of gravity. The strange matter MIT bag model equation of state (EoS) has been considered along with the usual forms of the Karori–Barua KB metric potentials. For this purpose, we derived the Einstein–Maxwell field equations in the assistance of strange matter EoS and KB type ansatz by employing the two viable and cosmologically well-consistent models of f R = R + γ R 2 and f R = R + γ R R + α R 2 . Thereafter, we have checked the physical acceptability of the proposed results such as pressure, energy density, energy conditions, TOV equation, stability conditions, mass function, compactness, and surface redshift by using graphical representation. Moreover, we have investigated that the energy density and radial pressure are nonsingular at the core or free from central singularity and always regular at every interior point of the compact sphere. The numerical values of such parameters along with the surface density, charge to radius ratio, and bag constant are computed for three well-known compact stars such as CS1 SAXJ 1808 . 4 − 3658 ( x ˜ = 7.07   km , CS2 VelaX − 1 x ˜ = 9.56   km , and CS3 4U1820 − 30 x ˜ = 10   km and are presented in Tables 1–6. Conclusively, we have noticed that our presented charged compact stellar object in the background of two well-known f R models obeys all the necessary conditions for the stable equilibrium position and which is also perfectly fit to compose the strange quark star object.

Charged anisotropic compact stars in Logarithmic-Corrected R2 gravity

2020 ◽  
Vol 35 (04) ◽  
pp. 2050013 ◽  
Author(s):  
M. Farasat Shamir ◽  
I. Fayyaz
Keyword(s):  
Energy Density ◽  
Electric Charge ◽  
Graphical Representation ◽  
Strong Electric Field ◽  
Compact Star ◽  
Compact Stars ◽  
Fluid Distribution ◽  
Anisotropic Fluid ◽  
Distribution Factor ◽  
Field Equations

We consider [Formula: see text] corrected model, i.e. [Formula: see text], where [Formula: see text] is the Ricci scalar and [Formula: see text], [Formula: see text] are arbitrary constant values, to investigate some of the interior configurations of static anisotropic spherical charged stellar structures. The existence of electric charge and a strong electric field confirms due to the higher values of pressure distribution and energy density of the matter inside the stars. Furthermore, for compact star configurations, we also consider the simplified MIT bag model equation of state (EoS) given by [Formula: see text], where [Formula: see text] is radial pressure, [Formula: see text] is energy density and [Formula: see text] is bag constant. This approach allows to find electric charge from the Einstein–Maxwell field equations. We have extensively discussed the behavior of the electric charge and anisotropic fluid distribution factor for five different values of [Formula: see text]. Interestingly, it is noticed during this study, for smaller values of [Formula: see text] we get intensity in electric charge. The Tolman–Oppenheimer–Volkoff equation (TOV), is modified in order to carry electric charge. In particular, we model the compact star candidates SAXJ 1808.4–3658 and Vela X-1 and give graphical representation of some important properties such as equilibrium condition, mass-radius ratio and surface redshift. In the end, our calculated solutions provide strong evidences for more realistic and viable charged stellar model.

Anisotropic compact stars model with generalized Bardeen–Hayward mass function

2021 ◽  
Vol 36 (26) ◽  
pp. 2150190
Author(s):  
Nayan Sarkar ◽  
Susmita Sarkar ◽  
Farook Rahaman ◽  
Ksh. Newton Singh
Keyword(s):  
Surface Density ◽  
Mass Function ◽  
Static Stability ◽  
Compact Stars ◽  
Energy Conditions ◽  
Causality Condition ◽  
Field Equations ◽  
Regular Black Hole ◽  
Bag Constant ◽  
Tov Equation

A new compact stars nonsingular model is presented with the generalized Bardeen–Hayward mass function. Generalized Bardeen–Hayward described the regular black hole, however, due to its regularity or nonsingular nature we were inspired to construct an anisotropic compact stars model. Along with the ansatz mass function, we coupled it with a linear equation of state (EoS) to find the solutions of field equations. Indeed, the new solutions are physically viable in all physical ground. The energy conditions and Tolman–Oppenheimer–Volkoff (TOV)-equation are well satisfied signifying that the mass distribution is physically possible and at equilibrium. Also, the static stability criterion, the causality condition and Abreu’s stability condition hold good and therefore configurations are physically static stable. The same condition is further supported by the condition that the adiabatic index, which is greater than the Newtonian limit, i.e. [Formula: see text]. It is also noticed that the bag constant [Formula: see text] is proportional to the surface density in our model.

scholarly journals A new class of relativistic model of compact stars of embedding class I

2017 ◽  
Vol 26 (09) ◽  
pp. 1750090 ◽  
Author(s):  
Piyali Bhar ◽  
Ksh. Newton Singh ◽  
Tuhina Manna
Keyword(s):  
Compact Star ◽  
Mass Function ◽  
Static Stability ◽  
Compact Stars ◽  
Stable Region ◽  
Energy Conditions ◽  
Arbitrary Form ◽  
Star Model ◽  
Field Equations ◽  
Anisotropic Matter

In the present paper, we have constructed a new relativistic anisotropic compact star model having a spherically symmetric metric of embedding class one. Here we have assumed an arbitrary form of metric function [Formula: see text] and solved the Einstein’s relativistic field equations with the help of Karmarkar condition for an anisotropic matter distribution. The physical properties of our model such as pressure, density, mass function, surface red-shift, gravitational redshift are investigated and the stability of the stellar configuration is discussed in details. Our model is free from central singularities and satisfies all energy conditions. The model we present here satisfy the static stability criterion, i.e. [Formula: see text] for [Formula: see text][Formula: see text]g/cm3(stable region) and for [Formula: see text][Formula: see text]g/cm3, the region is unstable i.e. [Formula: see text].

Analysis of compact stars in logarithmic-corrected R2 gravity

2019 ◽  
Vol 35 (02) ◽  
pp. 1950354 ◽  
Author(s):  
M. Farasat Shamir ◽  
Iffat Fayyaz
Keyword(s):  
Graphical Representation ◽  
Stellar Model ◽  
Compact Stars ◽  
Energy Conditions ◽  
Einstein Field Equations ◽  
Field Equations ◽  
Logarithmic Corrections ◽  
Proposed Model ◽  
Physical Tests ◽  
Surface Redshift

We discuss the existence of compact stars in the context of [Formula: see text] gravity model, where additional logarithmic corrections are assumed. Here, [Formula: see text] is the Ricci scalar and [Formula: see text], [Formula: see text] are constant values. Further, the compact stars are considered to be anisotropic in nature, due to the spherical symmetry and high density. For this purpose, we derive the Einstein field equations by considering Krori–Barua spacetime. For our proposed model, the physical acceptability is verified by employing several physical tests like the energy conditions, Herrera cracking concept and stability condition. In addition to this, we also discuss some important properties such as mass–radius relation, surface redshift and the speed of sound are analyzed. Our results are compared with observational stellar mass data, namely, 4U 1820-30, Cen X-3, EXO 1785-248 and LMC X-4. The graphical representation of obtained solutions provide strong evidences for more realistic and viable stellar model.

GRAVITATIONAL COLLAPSE OF AN ANISOTROPIC FLUID WITH SELF-SIMILARITY OF THE SECOND KIND

2006 ◽  
Vol 15 (09) ◽  
pp. 1407-1417 ◽  
Author(s):  
C. F. C. BRANDT ◽  
R. CHAN ◽  
M. F. A. DA SILVA ◽  
JAIME F. VILLAS DA ROCHA
Keyword(s):  
Black Hole ◽  
Naked Singularity ◽  
Radial Pressure ◽  
The Self ◽  
Energy Conditions ◽  
Anisotropic Fluid ◽  
Einstein Field Equations ◽  
Field Equations ◽  
Self Similarity ◽  
Self Similar

We study the evolution of an anisotropic fluid with kinematic self-similarity of the second kind. We found a class of solution to the Einstein field equations by assuming an equation of state where the radial pressure of the fluid is proportional to its energy density (pr = ωρ) and that the fluid moves along time-like geodesics. The self-similarity requires ω = -1. The energy conditions, geometrical and physical properties of the solutions are studied. We have found that, depending on the self-similar parameter α, they may represent a black hole or a naked singularity.

scholarly journals Relativistic compact stars in Tolman spacetime via an anisotropic approach

2021 ◽  
Vol 81 (6) ◽  
Author(s):  
Piyali Bhar ◽  
Pramit Rej ◽  
P. Mafa Takisa ◽  
M. Zubair
Keyword(s):  
Graphical Representation ◽  
Dimensional Space ◽  
Compact Star ◽  
Compact Stars ◽  
Stellar Structure ◽  
Energy Conditions ◽  
Anisotropic Pressure ◽  
Model Parameters ◽  
Theory Of Relativity ◽  
Field Equations

AbstractIn this present work, we have obtained a singularity-free spherically symmetric stellar model with anisotropic pressure in the background of Einstein’s general theory of relativity. The Einstein’s field equations have been solved by exploiting Tolman ansatz [Richard C Tolman, Phys. Rev. 55:364, 1939] in $$(3+1)$$ ( 3 + 1 ) -dimensional space-time. Using observed values of mass and radius of the compact star PSR J1903+327, we have calculated the numerical values of all the constants from the boundary conditions. All the physical characteristics of the proposed model have been discussed both analytically and graphically. The new exact solution satisfies all the physical criteria for a realistic compact star. The matter variables are regular and well behaved throughout the stellar structure. Constraints on model parameters have been obtained. All the energy conditions are verified with the help of graphical representation. The stability condition of the present model has been described through different testings.

N-DIMENSIONAL GRAVITATIONAL COLLAPSE WITH DARK ENERGY

2008 ◽  
Vol 17 (08) ◽  
pp. 1295-1309
Author(s):  
R. S. GONÇALVES ◽  
JAIME F. VILLAS DA ROCHA
Keyword(s):  
Dark Energy ◽  
Radial Pressure ◽  
The Self ◽  
Energy Conditions ◽  
Anisotropic Fluid ◽  
Einstein Field Equations ◽  
Field Equations ◽  
Self Similarity ◽  
Naked Singularities ◽  
Self Similar

We study the evolution of an N-dimensional anisotropic fluid with kinematic self-similarity of the second kind and find a class of solutions to the Einstein field equations by assuming an equation of state where the radial pressure of the fluid is proportional to its energy density (pr= ωρ) and that the fluid moves along timelike geodesics. As in the four-dimensional case, the self-similarity requires ω = -1. The energy conditions and geometrical and physical properties of the solutions are studied. We find that, depending on the self-similar parameter α, they may represent black holes or naked singularities. We also study the presence of dark energy in some models, and find that their existence gives rise to some constraints on the dimensions of the space–times.

scholarly journals ON THE BLACK HOLE INTERIOR SPACETIME

2009 ◽  
Vol 24 (08n09) ◽  
pp. 1593-1597 ◽  
Author(s):  
HRISTU CULETU
Keyword(s):  
Black Hole ◽  
Energy Density ◽  
Cosmological Constant ◽  
Bulk Viscosity ◽  
Radial Pressure ◽  
Time Dependent ◽  
Energy Conditions ◽  
Anisotropic Fluid ◽  
Viscosity Coefficients ◽  
Black Hole Interior

A spacetime endowed with an anisotropic fluid is proposed for the interior of a black hole. The geometry has an instantaneous Minkowski form and is a solution of Einstein's equations with a stress tensor on the r.h.s. obeying all the energy conditions. The interior fluid is compressible, with time dependent shear and bulk viscosity coefficients. The energy density ρ and the "radial" pressure p are proportional to 1/t2, with no pressures on θ- and ϕ- directions. The model leads to a time dependent cosmological constant.

Quintessence compact stars with Vaidya–Tikekar type grr for anisotropic fluid

2020 ◽  
Vol 98 (9) ◽  
pp. 869-876
Author(s):  
G. Abbas ◽  
M.R. Shahzad
Keyword(s):  
Killing Vector ◽  
Graphical Analysis ◽  
Compact Stars ◽  
Energy Conditions ◽  
Anisotropic Fluid ◽  
Conformal Killing ◽  
Field Equations ◽  
Anisotropic Matter ◽  
Quintessence Field ◽  
Analytical Expressions

The present study provides a new solution to the Einstein field equations for anisotropic matter configuration in static and spherically symmetric space–time. By taking benefit from the conformal Killing vector (CKV) technique and quintessence field specified by a parameter ωq as –1 < ωq < –1/3, we generate an exact solution to the field equations. For this investigation, we have used a specific form of metric potential taken fromVaidya–Tikekar (J. Astrophys. Astron. 3, 325 (1982)) geometry. To canvass the physical plausibility of the presented solution, we explored some analytical expressions such as energy conditions, the TOV equation, stability analysis, and equation of state parameters. We present graphical analysis of the necessary analytical expressions that revealed that our solution satisfies the necessary physical conditions.

f(T) gravity and static wormhole solutions

2014 ◽  
Vol 29 (27) ◽  
pp. 1450137 ◽  
Author(s):  
Muhammad Sharif ◽  
Shamaila Rani
Keyword(s):  
Equation Of State ◽  
Energy Density ◽  
Radial Pressure ◽  
Energy Conditions ◽  
Spherically Symmetric ◽  
Shape Functions ◽  
Field Equations ◽  
Torsion Scalar ◽  
Transverse Pressure

In this paper, we study static spherically symmetric wormhole solutions in the framework of f(T) gravity, where T represents torsion scalar. We consider non-diagonal tetrad and anisotropic distribution of the fluid. We construct expressions for matter components such as energy density, radial pressure and transverse pressure from the field equations. Taking into account a particular equation of state (EoS) in terms of traceless fluid, we discuss the behavior of energy conditions for wormhole solutions with well-known f(T) and shape functions. We conclude that physically acceptable static wormhole solutions are obtained for both these functions.

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