Relativistic Modelling of Stable Anisotropic Super-Dense Star

Canadian Journal of Physics, 2018

Inithis article, authorsihave discussed theinew exactimodel of anisotropicistar in f (T) theory ofigravity. The parametric form of imetric functions has ibeen implementedito solveithe dynamicaliequations in f (T) theoryiwith theianisotropic fluid. Theinovelty of theiwork isithat the obtainedisolutions doinot containisingularity butipotentially stable. Theiestimated valuesifor mass andiradius of theidifferent strangeistars RX J 1856-37, Her X-1, and Vela X-12 haveibeen utilizedito figure theivalues of unknowniconstants in Kroriiand Baruaimetric. The physicaliparameters likeianisotropy, stabilityiand redshiftiof theistars have beeniexamined inidetail.

In this paper, an anisotropic relativistic fluid sphere with variable density, which decreases along the radius and is maximum at the centre, is discussed. Spherically symmetric static space-time with spheroidal physical 3-space is considered. The source is an anisotropic fluid. The solution is an anisotropic generalization of the solution discussed by Vaidya and Tikekar [1]. The physical three space constant time has spheroidal solution. The line element of the solution can be expressed in the form Patel and Desai [2]. The material density is always positive. The solution efficiently matches with Schwarzschild exterior solution across the boundary. It is shown that the model is physically reasonable by studying the numerical estimates of various parameters. The density vs radial pressure relation in the interior is discussed numerically. An anisotropy effect on the redshift is also studied numerically.

The European Physical Journal C

We present an algorithm to generalize a plethora of well-known solutions to Einstein field equations describing spherically symmetric relativistic fluid spheres by relaxing the pressure isotropy condition on the system. By suitably fixing the model parameters in our formulation, we generate closed-form solutions which may be treated as an anisotropic generalization of a large class of solutions describing isotropic fluid spheres. From the resultant solutions, a particular solution is taken up to show its physical acceptability. Making use of the current estimate of mass and radius of a known pulsar, the effects of anisotropic stress on the gross physical behaviour of a relativistic compact star is also highlighted.

The European Physical Journal C, 2015

In this work some families of relativistic anisotropic charged fluid spheres have been obtained by solving the Einstein-Maxwell field equations with a preferred form of one of the metric potentials, and suitable forms of electric charge distribution and pressure anisotropy functions. The resulting equation of state (EOS) of the matter distribution has been obtained. Physical analysis shows that the relativistic stellar structure for the matter distribution considered in this work may reasonably model an electrically charged compact star whose energy density associated with the electric fields is on the same order of magnitude as the energy density of fluid matter itself (e.g., electrically charged bare strange stars). Furthermore these models permit a simple method of systematically fixing bounds on the maximum possible mass of cold compact electrically charged self-bound stars. It has been demonstrated, numerically, that the maximum compactness and mass increase in the presence of an electric field and anisotropic pressures. Based on the analytic models developed in this present work, the values of some relevant physical quantities have been calculated by assuming the estimated masses and radii of some well-known potential strange star candidates like

The European Physical Journal C, 2016

In this article we obtain a new anisotropic solution for Einstein's field equations of embedding class one metric. The solution represents realistic objects such as Her X-1 and RXJ 1856-37. We perform a detailed investigation of both objects by solving numerically the Einstein field equations with anisotropic pressure. The physical features of the parameters depend on the anisotropic factor i.e. if the anisotropy is zero everywhere inside the star then the density and pressures will become zero and the metric turns out to be flat. We report our results and compare with the above mentioned two compact objects as regards a number of key aspects: the central density, the surface density onset and the critical scaling behaviour, the effective mass and radius ratio, the anisotropization with isotropic initial conditions, adiabatic index and red shift. Along with this we have also made a comparison between the classical limit and theoretical model treatment of the compact objects. Finally we discuss the implications of our findings for the stability condition in a relativistic compact star.

2014

In this work some families of relativistic anisotropic charged fluid spheres have been obtained by solving Einstein-Maxwell field equations with the preferred form of one of the metric potentials, a suitable forms of electric charge distribution and pressure anisotropy functions. The resulting equation of state (EOS) of the matter distribution has been obtained. Physical analysis shows that the relativistic stellar structure for matter distribution obtained in this work may reasonably model an electrically charged compact star whose energy density associated with the electric fields is on the same order of magnitude as the energy density of fluid matter itself (e.g. electrically charged bare strange stars). These models permit a simple method of systematically fixing bounds on the maximum possible mass of cold compact electrically charged self-bound stars. It has been demonstrated numerically that the maximum compactness and mass increase in the presence of electric field and anisotropic pressures. Based on the analytic model developed in this present work, the values of the relevant physical quantities have been calculated by assuming the estimated masses and radii of some well known potential strange star candidates like PSR

We present a class of exact solutions of Einstein's gravitational field equations describing spherically symmetric and static anisotropic stellar type configurations. The solutions are obtained by assuming a particular form of the anisotropy factor. The energy density and both radial and tangential pressures are finite and positive inside the anisotropic star. Numerical results show that the basic physical parameters (mass and radius) of the model can describe realistic astrophysical objects like neutron stars.

European physical journal. C, Particles and fields, 2024

We report here a new exact solution of the Einstein field equations that describes a static spherically symmetric, anisotropic compact stellar fluid sphere. A generalized metric form corresponding to the g rr component and a specific anisotropic profile generates the model. The new class of generalized solutions reduces to Finch-Skea, Vaidya Tikekar and Schwarzschild interior solutions for specific choices of the model parameters. The model parameters have been determined from the continuity of the interior and exterior metrics at the surface of the star and setting the radial pressure at the boundary to zero. Recent observed measurements from some pulsars as sources have been utilized to validate our model.

University of North Bengal, 2021

In this paper, we have derived a class of analytical solutions of Einstein fi eld equations for a spherically symmetric anisotropic matter distribution. By choosing one of the metric potentials grr to be Krori-Barua metric type and a specific choice of anisotropy we obtain the other metric function. The interior solutions thus obtained has been utilized to construct a potentially stable model that could describe compact stellar objects. The exterior vacuum region has been assigned with the Schwarzschild spacetime metric. Across the boundary of the compact star where the radial pressure drops to zero, the interior metric has been matched smoothly wit h the exterior metric to fix t he model parameters associated with t he solutions. All the regularity conditions, energy conditions and all other physical requirements demanded for a realistic compact system has been shown to satisfy graphically with this model corresponding to the pulsars 4U1820-30 (Mass= l.58M0 and radius= 9.1 km) [1] and Gen X-3 (Mass= l.49M0 and radius= 10.136 km)[2]. The stability of the model is also discussed using some of the known stability criterion namely TOV equation, adiabatic index, Buchdahl condition and Herrera's cracking concept etc. The wide applicability of our developed model has been justified with the numerical values of current observational data set from various other known compact stars to a high degree of accuracy.

The European Physical Journal C, 80(5): 371, 2020

In this work, a spherically symmetric and static relativistic anisotropic fluid sphere solution of the Einstein field equations is provided. To build this particular model, we have imposed metric potential e 2λ(r) and an equation of state. Specifically, the so-called modified generalized Chap-lygin equation of state with ω = 1 and depending on two parameters, namely, A and B. These ingredients close the problem, at least mathematically. However, to check the feasibility of the model, a complete physical analysis has been performed. Thus, we analyze the obtained geometry and the main physical observables, such as the density ρ, the radial p r , and tangential p t pressures as well as the anisotropy factor . Besides, the stability of the system has been checked by means of the velocities of the pressure waves and the rel-ativistic adiabatic index. It is found that the configuration is stable in considering the adiabatic index criteria and is under hydrostatic balance. Finally, to mimic a realistic compact object, we have imposed the radius to be R = 9.5 [km]. With this information and taking different values of the parameter A the total mass of the object has been determined. The resulting numerical values for the principal variables of the model established that the structure could represent a quark (strange) star mixed with dark energy.