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.

scholarly journals Analysis of charged compact stars in modified gravity

2018 ◽  
Vol 27 (08) ◽  
pp. 1850082 ◽  
Author(s):  
M. Farasat Shamir ◽  
Saeeda Zia
Keyword(s):  
Modified Gravity ◽  
Compact Star ◽  
Compact Object ◽  
Relative Difference ◽  
Comprehensive Analysis ◽  
Compact Stars ◽  
Energy Conditions ◽  
Anisotropic Pressure ◽  
Field Equations ◽  
Stability Energy

Current study highlights the physical characteristics of charged anisotropic compact stars by exploring some exact solutions of modified field equations in [Formula: see text] gravity. A comprehensive analysis is performed from the obtained solutions regarding stability, energy conditions, regularity, sound velocity and compactness. These solutions can be referred to model the compact celestial entities. In particular, a compact star named, [Formula: see text] has been modeled which indicates that current solution fits and is in conformity to the observational data as well. A useful and interesting fact from this model arises that relative difference between two forces of anisotropic pressure and electromagnetic force may occur inside the aforementioned compact star. This is another mechanism which is essential for stability of the compact object and prevent stellar object to annihilate.

Anisotropic solution for compact star in 5D Einstein–Gauss–Bonnet gravity

2021 ◽  
Vol 36 (32) ◽  
Author(s):  
S. K. Maurya ◽  
Anirudh Pradhan ◽  
Ayan Banerjee ◽  
Francisco Tello-Ortiz ◽  
M. K. Jasim
Keyword(s):  
Compact Star ◽  
Compact Objects ◽  
Compact Stars ◽  
Stellar Structure ◽  
Energy Conditions ◽  
Field Equations ◽  
Anisotropic Solution ◽  
Bonnet Gravity ◽  
Spacetime Geometry ◽  
Equilibrium Configurations

In astronomy, the study of compact stellar remnants — white dwarfs, neutron stars, black holes — has attracted much attention for addressing fundamental principles of physics under extreme conditions in the core of compact objects. In a recent argument, Maurya et al. [Eur. Phys. J. C 77, 45 (2017)] have proposed an exact solution depending on a specific spacetime geometry. Here, we construct equilibrium configurations of compact stars for the same spacetime that make it interesting for modeling high density physical astronomical objects. All calculations are carried out within the framework of the five-dimensional Einstein–Gauss–Bonnet gravity. Our main interest is to explore the dependence of the physical properties of these compact stars depending on the Gauss–Bonnet coupling constant. The interior solutions have been matched to an exterior Boulware–Deser solution for [Formula: see text] spacetime. Our finding ensures that all energy conditions hold, and the speed of sound remains causal, everywhere inside the star. Moreover, we study the dynamical stability of stellar structure by taking into account the modified field equations using the theory of adiabatic radial oscillations developed by Chandrasekhar. Based on the observational data for radii and masses coming from different astronomical sources, we show that our model is compatible and physically relevant.

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.

Charged stellar structure in Tolman–Kuchowicz spacetime

2020 ◽  
Vol 17 (09) ◽  
pp. 2050140
Author(s):  
M. Farasat Shamir ◽  
I. Fayyaz
Keyword(s):  
Compact Star ◽  
Physical Stability ◽  
Stellar Model ◽  
Stellar Structure ◽  
Energy Conditions ◽  
Physical Parameters ◽  
Field Equations ◽  
Charged Fluid ◽  
Charged Fluid Sphere ◽  
Anisotropic Factor

In this paper, we have presented the Einstein–Maxwell equations which are described by the spherically symmetric spacetime in the presence of charge by exploiting the Tolman–Kuchowicz spacetime. The corresponding field equations are constructed and the form of charge distribution is chosen to be [Formula: see text], where [Formula: see text] is a constant quantity. We also find the values of unknown constants from junction conditions and discuss the behavior of effective energy density, effective radial and tangential pressure and anisotropic factor with two viable [Formula: see text] models. We examine the physical stability of charged stellar structure through energy conditions, causality and stability condition. We use modified form of TOV equation for anisotropic charged fluid sphere to analyze the equilibrium condition. In this work, we model the compact star candidate SAXJ 1808.4 – 3658 and study the compactness level and anisotropic behavior corresponding to the variation of physical parameters which are involved in [Formula: see text] models. Further, we evaluate some important properties such as mass-radius ratio compactness factor and surface redshift. It is depicted from this study that the obtained solutions provide strong evidences for more realistic and viable stellar model.

scholarly journals Constraining values of bag constant for strange star candidates

2019 ◽  
Vol 28 (13) ◽  
pp. 1941006 ◽  
Author(s):  
Abdul Aziz ◽  
Saibal Ray ◽  
Farook Rahaman ◽  
M. Khlopov ◽  
B. K. Guha
Keyword(s):  
Compact Star ◽  
A Priori ◽  
Stellar System ◽  
Mass Function ◽  
Strange Star ◽  
Compact Stars ◽  
Stellar Structure ◽  
Star Model ◽  
Field Equations ◽  
Bag Constant

We provide a strange star model under the framework of general relativity by using a general linear equation of state (EOS). The solution set thus obtained is employed on altogether 20 compact star candidates to constraint values of MIT bag model. No specific value of the bag constant ([Formula: see text]) a priori is assumed, rather possible range of values for bag constant is determined from observational data of the said set of compact stars. To do so, the Tolman–Oppenheimer–Volkoff (TOV) equation is solved by homotopy perturbation method (HPM) and hence we get a mass function for the stellar system. The solution to the Einstein field equations represents a nonsingular, causal and stable stellar structure which can be related to strange stars. Eventually, we get an interesting result on the range of the bag constant as [Formula: see text]. We have found the maximum surface redshift [Formula: see text] and shown that the central redshift ([Formula: see text]) cannot have value larger than [Formula: see text], where [Formula: see text]. Also, we provide a possible value of bag constant for neutron star with quark core using hadronic as well as quark EOS.

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.

scholarly journals Strange star with Krori–Barua potential in the presence of anisotropy

2021 ◽  
pp. 2150097
Author(s):  
Piyali Bhar
Keyword(s):  
General Theory ◽  
Compact Star ◽  
Vacuum Solution ◽  
Compact Stars ◽  
Theory Of Relativity ◽  
General Theory Of Relativity ◽  
Field Equations ◽  
Dimensional Spacetime ◽  
The Stability ◽  
Text Component

In this paper, a well-behaved new model of anisotropic compact star in (3+1)-dimensional spacetime has been investigated in the background of Einstein’s general theory of relativity. The model has been developed by choosing [Formula: see text] component as Krori–Barua (KB) ansatz [Krori and Barua in J. Phys. A, Math. Gen. 8 (1975) 508]. The field equations have been solved by a proper choice of the anisotropy factor which is physically reasonable and well behaved inside the stellar interior. Interior spacetime has been matched smoothly to the exterior Schwarzschild vacuum solution and it has also been depicted graphically. Model is free from all types of singularities and is in static equilibrium under different forces acting on the system. The stability of the model has been tested with the help of various conditions available in literature. The solution is compatible with observed masses and radii of a few compact stars like Vela X-1, 4U [Formula: see text], PSR J[Formula: see text], LMC X [Formula: see text], EXO [Formula: see text].

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.

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.

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