Anisotropic Compact Star Models Research Articles

Study on physical properties and maximum mass limit of Finch–Skea anisotropic model under Karmarkar condition in [formula omitted]-gravity

The primary objective of this work is to study the dynamical characteristics of an anisotropic compact star model with spherical symmetry. This investigation is conducted in the framework of modified f(Q) gravity. To simplify the calculations, we employ the Karmarkar condition and derive a differential equation that establishes a relationship between two crucial components of the spacetime namely eν and eλ. Additionally, we incorporate the well-known Finch–Skea structure as the component representing grr and subsequently find the resulting form of the component gtt from the relation of metric functions to formulate the precise solutions for the stellar structure. To assess the behavior of the anisotropic fluid and stability of the compact star, we use the observed values of mass and radius for the compact star model PSRJ0437−4715. The graphical analysis depicts that the stellar structure possesses physical viability and exhibits intriguing properties. Furthermore, we predicted the mass–radius relation along with the maximum mass limit of several objects for different parameter values by assuming two different surface densities. It is discovered that the compactness rises when density increases.

Impact of [formula omitted] gravity on anisotropic compact star model and stability analysis

The aim of this study is to explore the relativistic anisotropic configuration of a hybrid star in the proximity of strange quark matter and normal baryonic matter within the context of f(Q) theory of gravity. To associate pressure and density due to strange quark matter, the MIT bag model equation of state has been exploited. Here, for establishing the dynamical equations, the Krori–Barua ansatz and a linear form of f(Q) have been considered. We further utilize the Schwarzschild metric as an exterior geometry to find the unknown parameters. Furthermore, several physical properties such as energy density, pressure components, anisotropy, sound speeds, energy conditions, compactness factor, etc., have been analyzed through the graphical representation. Additionally, the variation of bag constant Bg and the measurement of the mass have been examined through contour plots. We further study the mass–radius (M−R) relation to determine the maximum permitted mass. According to our analysis, the maximum mass of a hybrid star rises to more than 2 M⊙ when ‘m’ is decreased. For instance, with m=0.2, the mass of the hybrid star is about 2.6M⊙, which is in the lower mass gap and corresponds to the mass of the lighter component of the GW190814 event. Finally, our investigation validates the stability of the suggested model. We came to the conclusion that f(Q) gravity theory can produce super massive hybrid stars and provide a plausible explanation of the M−R relation that satisfies the observable constraints.

Relativistic polytropic models of charged anisotropic compact objects

In this paper, we introduce new viable solutions to the Einstein-Maxwell field equations by incorporating the features of anisotropic matter distributions within the realm of the general theory of relativity (). To obtain these solutions, we employed the Finch-Skea spacetime, along with a generalized polytropic equation of state (). We constructed various models of generalized polytropes by assuming different values of the polytropic index, i.e., , and . Next, numerous physical characteristics of these considered models were studied via graphical analysis, and they were found to obey all the essential conditions for astrophysical compact objects. Furthermore, such outcomes of charged anisotropic compact star models could be reproduced in various other cases including linear, quadratic, and polytropic

Anisotropic compact stars in presence of electromagnetic field, quintessence field and cosmological constant in f(G) gravity

In this work, we have discussed the anisotropic compact stars in the framework of modified Gauss–Bonnet gravity, named by f(G) theory of gravity. We have found the equations of motion of stars with respect to spherically symmetric metric, describing interior geometry of the compact stellar object, anisotropic mode of the matter distribution in the presence of electromagnetic field and quintessence field. We have taken the metric coefficients in the form [Formula: see text] and [Formula: see text] as well as a particular form of [Formula: see text], where the powers and coefficients of r are constants. The unknown constants are evaluated by matching between interior and exterior Reissner–Nordström–de Sitter metric. We have analyzed some physical aspects like energy density, radial and tangential pressures, anisotropic parameter of matter distribution, energy conditions, mass-radius relation, compactness factor, surface redshift, and stability of our resulting solutions through graphical behavior by comparing to the observational data of different types of compact stars like 4U1820-30, Vela X-1 and SAXJ1808.4-3658. We conclude that all physical attributes maintain their experimental ranges which deliver our anisotropic compact star models are viable and also stable upto certain region in [Formula: see text] gravity theory.

Quintessence compact star models under embedded class one symmetry

In this article, we have investigated anisotropic compact star models threaded by quintessence matter contents in the background of embedded class one spacetime. The proposed models are characterized by parameterωq with in a range −1<ωq<−13and satisfying the equation of state pr=αρ. We have studied the essential physical features of the models in detail graphically as well as analytically. The stability status of the models is ascertained via different well defined criteria in general theory of relativity. The causality condition is well obeyed by our models. We have executed the extensive analysis of the models for the stars LMC X-4 and Vela X-1 having masses 1.04MΘ&1.77MΘ wheres as the radii are 8.301 km and 9.56 km respectively.

Physical aspects of anisotropic compact stars in gravity with off diagonal tetrad

This study addresses the formation of anisotropic compact star models in the background of gravity (where T and represent the torsion and trace of the energy momentum tensor, respectively). gravity is an extension of the theory, and it allows a general non-minimal coupling between T and . In this setup, we apply Krori and Barua's solution to the static spacetime with the components and . To develop viable solutions, we select a well-known model (where αand β are coupling parameters, and ϕ indicates the cosmological constant). We adopt the conventional matching of interior and exterior space time to evaluate the unknowns, which are employed in the stellar configuration. We present a comprehensive discussion on the stellar properties to elaborate the anisotropic nature of compact stars corresponding to well-known models: , , , , and . Via physical analysis, it is observed that the solution of compact spheres satisfy the acceptability criteria, and its models behave optimally and depict stability and consistency, in accordance with gravity.

Anisotropic compact star models in f(T) gravity with Tolman–Kuchowicz spacetime

The purpose of this work is to present stellar models for anisotropic matter distribution in the framework of [Formula: see text] gravity with torsion scalar [Formula: see text]. In this regard, we use the interior geometry of Tolman–Kuchowicz spacetime having the potential components of the form [Formula: see text] and [Formula: see text], where [Formula: see text], [Formula: see text], [Formula: see text] and [Formula: see text] are constants which have been evaluated with the aid of matching conditions on the surface of interior and exterior spacetimes. Off-diagonal tetrad is used to obtain the modified Field Equations (FEs). We use power law of [Formula: see text] gravity to get all the physical parameters such as principal stresses, density. We discuss anisotropy of the system and its effects on the system. The physical analysis is also presented by measuring speeds of sound, equilibrium conditions, energy conditions and redshift, etc. We choose some compact star models to present graphical description of the solution.

Analysis of physically realizable stellar models in embedded class one spacetime manifold

In this paper, we searched two new exact solutions of Einstein’s field equations for modeling of compact cold stars using embedded class one spacetime continuum. We find out the expressions for pressure, density, anisotropy, redshift, metric potentials and other physical variables in terms of algebraic and trigonometric expressions and observe that all variables show well-behaved trends inside the compact stellar configurations. The causality condition is well maintained by our stellar models, i.e. the radial velocity and transverse velocity are less than l. The stability of our models is assessed via different stability criteria. The Buchdahl condition holds good for our solution. Herrera’s cracking method is applied to check the stability of stellar models. We generate anisotropic compact star models, whose masses and radii are in close agreement with the observed values for compact stars 4U 1538-52, LMCX-4, PSRJ1614-2230. A comparative analysis of the proposed models is carried out based on two different solutions reported in the paper. The appropriate graphical analysis is provided to authenticate the viability of the models.

Generalized relativistic anisotropic compact star models by gravitational decoupling

In this work we have extended the Maurya-Gupta isotropic fluid solution to Einstein field equations to an aniso-tropic domain. To do so, we have employed the gravitational decoupling via the minimal geometric deformation approach. The present model is representing the strange star candidate LMC X-4. A mathematical, physical and graphical analysis, shown that the obtained model fulfills all the criteria to be an admissible solution of the Einstein field equations. Specifically, we have analyzed the regularity of the metric potentials and the effective density, radial and tangential pressures within the object, causality condition, energy conditions, equilibrium via Tolman–Oppenheimer–Volkoff equation and the stability of the model by means of the adiabatic index and the square of subliminal sound speeds.

A new generalised solution to generate anisotropic compact star models in the Karmarkar space-time manifold

In the present article a new generalised solution is obtained for anisotropic matter configuration using Karmarkar’s condition. The solution is used to model the interior structure of anisotropic relativistic objects as it satisfies all necessary physical conditions. The pressure, density and metric potentials are free from any singularities and exhibit well behaved nature inside the anisotropic fluid sphere. The TOV equation is well maintained within the stellar configuration and all energy conditions hold good. The causality condition is well satisfied for our stellar models and stability of compact star models is further verified via Herrera’s cracking method. Harrison-Zeldovich-Novikov criterion for stability is also satisfied by our model. The adiabatic index is greater than $\frac{4}{3}$ throughout the stellar interior and the compactification factor also lies within the Buchdahl limit i.e. $M/R \le 4/9$ . We investigate the models for two compact stars PSRJ0348+0432 and SAX J1808.4-3658 within the framework of the general theory of relativity. The estimated mass and radius are in close agreement with the observational data. we extensively study the solutions corresponding to compact star PSRJ0348+0432 for $ n = 0, 1, 2, 3, 4, 4.5$ and the detailed graphical analysis is provided to substantiate the viability of the compact star model. One specific feature of our solution is that for large values of n, i.e. for $ n > 5$ solution reduces to Finch and Skea type solution.

Charged anisotropic compact objects by gravitational decoupling

In the present article, we have constructed a static charged anisotropic compact star model of Einstein field equations for a spherically symmetric space-time geometry. Specifically, we have extended the charged isotropic Heintzmann solution to an anisotropic domain. To address this work, we have employed the gravitational decoupling through the so called minimal geometric deformation approach. The charged anisotropic model is representing the realistic compact objects such as RXJ1856-37 and SAX J1808.4-3658(SS2). We have reported our results in details for the compact star RXJ1856-37 on the ground of physical properties such as pressure, density, velocity of sound, energy conditions, stability conditions, Tolman–Oppenheimer–Volkoff equation and redshift etc.

Anisotropic compact star models in Karmarkar space time continuum

In the present article, we have explored some new anisotropic compact star models by using embedded class one space time metric. We proceed our calculations by assuming a particular form of $g_{rr}$ metric potential and solved for the other metric $g_{tt}$ using Karmarkar condition. The matter density, radial pressure, tangential pressure, mass function, surface red-shift, anisotropy are all well behaved inside the fluid sphere. The solution satisfies all energy conditions i.e. strong energy condition, null energy condition, dominant energy condition and weak energy condition. The solution also satisfies the causality condition and can represent stable stellar fluid system as the adiabatic index $\varGamma > 4/3$ and the stability factor $-1\leq v_{t}^{2}-v_{r}^{2}\leq 0$ holds good inside the fluid sphere. We have framed our solution for two compact stars PSR J1614-2230 and SAX J1808.4-3658, which are well-behaved in all respects. The mass and radius of the compact stars PSR J1614-2230 and SAXJ1808.4-3658, obtained from the models are very close to the observational data proposed by Gangopadhyay et al. (Mon. Not. R. Astron. Soc. 431:3216, 2013) and Bhattacharya (2001) respectively.

Analytical study of anisotropic compact star models

A simple classification is given of the anisotropic relativistic star models, resembling the one of charged isotropic solutions. On the ground of this database, and taking into account the conditions for physically realistic star models, a method is proposed for generating all such solutions. It is based on the energy density and the radial pressure as seeding functions. Numerous relations between the realistic conditions are found and the need for a graphic proof is reduced just to one pair of inequalities. This general formalism is illustrated with an example of a class of solutions with linear equation of state and simple energy density. It is found that the solutions depend on three free constants and concrete examples are given. Some other popular models are studied with the same method.

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

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].

A New Charged Anisotropic Compact Star Model in General Relativity

In the present article, we explore a new static, spherically symmetric charged anisotropic fluid model of compact star in curvature coordinates. We consider metric potential g44 of Durgapal’s fifth solution [1] with a specific choice of electric field intensity E and physically acceptable expression of anisotropy factor Δ , which involve parameters K (charge) and Δ (anisotropy) respectively. The solution so obtained is utilized to construct the model for superdense star like neutron star. We have analysed that corresponding to X=0.1, K=2.8, a=1.6 and by assuming surface density , the mass of the compact star comes out to be with radius 14.51 kms, which closely resembles to that of PSRJ0348 + 0432. The solution is well behaved for the values of K satisfying 1≤K5. Our model is described analytically as well as with the help of graphical representations. Our solution is well behaved and free from any central singularity. It also satisfies all the energy conditions as well as the causality condition thus reconfirming the stability of our model.

Well behaved anisotropic compact star models in general relativity

Anisotropic compact star models have been constructed by assuming a particular form of a metric function \(e^{\lambda}\). We solved the Einstein field equations for determining the metric function \(e^{\nu}\). For this purpose we have assumed a physically valid expression of radial pressure (\(p_{r}\)). The obtained anisotropic compact star model is representing the realistic compact objects such as PSR 1937 +21. We have done an extensive study about physical parameters for anisotropic models and found that these parameters are well behaved throughout inside the star. Along with these we have also determined the equation of state for compact star which gives the radial pressure is purely the function of density i.e. \(p_{r}=f(\rho)\).

Modelling of anisotropic compact stars of embedding class one

In the present article, we have constructed static anisotropic compact star models of Einstein field equations for the spherical symmetric metric of embedding class one. By assuming the particular form of metric function $\nu$, We have solved the Einstein field equations for anisotropic matter distribution. The anisotropic models are representing the realistic compact objects such as SAX J 1808.4-3658 (SS1), Her X - 1, Vela X-12, PSR J1614-2230 and Cen X - 3. We have reported our results in details for compact star Her X-1 on the ground of physical properties such as pressure, density, velocity of sound, energy conditions, TOV equation and red-shift etc. Along with these, we have also discussed about stability of the compact star models. Finally we made the comparison between our anisotropic stars with the realistic objects on the key aspects as central density, central pressure, compactness and surface red-shift.

Anisotropic generalization of Matese &amp; Whitman solution for compact star models in general relativity

We present a detailed investigation of the stability of anisotropic compact star models by introducing Matese and Whitman (Phys. Rev. D 11:1270, 1980) solution in general relativity. We have particularly looked into the detailed investigation of the measurements of basic physical parameters such as radial pressure, tangential pressure, energy density, red shift, sound velocity, masses and radii are affected by unknown effects such as loss, accretion and diffusion of mass. Those give insight into the characteristics of the compact astrophysical object with anisotropic matter distribution as well as the physical reality. The results obtained for the physical feature of compact stars such as, Her. X-1, RXJ 1856-37, SAX J1808.4-3658(SS2) and SAX J1808.4-3658(SS1) are compared to the recently observed massive compact object.