Narrow Results

This paper proposes a new framework to investigate the spherically symmetric of anisotropic stars with clouds of strings and quintessence field in Rastall gravity. We develop the field equations in a spherically symmetric space–time with a quintessence field and clouds of string. We utilize the mass and radius of Her X-1, Vela X-1, SMC X-1, SAX J1808 0.4-3658 and 4 U 1538-52, which are well mentioned in the literature. We applied the matching conditions by considering outer space calculated in Rastall gravity to evaluate the constants parameters. To check the stability and physical presence of compact models, we computed the most important features of quintessence stars in the presence of a cloud of strings. We explored characteristics including energy density, quintessence density, radial pressure, tangential pressure gradients, anisotropic factor, energy conditions, sound speeds, TOV forces, EoS components, mass function, compactification and redshift.

I report on recent work concerning the existence and stability of self-gravitating spheres with anisotropic pressure. After presenting new exact solutions, Chandrasekhar's variational formalism for radial perturbations is generalized to anisotropic objects and applied to investigate their stability. It is shown that anisotropy can not only support stars of mass M and radius R with 2M/R≥8/9 and arbitrarily large surface redshifts, but that stable configurations exist for values of the adiabatic index γ smaller than the corresponding isotropic value.

In this paper, we study the anisotropy of charged relativistic stars. We show that the structure of the star is changed by the electric field and this electric field destroys the isotropy of the star making the radial component of the energy–momentum tensor different from the angular ones. Charged compact stars have already been studied by Bekenstein [Phys. Rev. D4 (1971) 2185] and anisotropic stars were reviewed recently [Gen. Relativ. Gravit.34 (2002) 1793]. We present the solutions obtained in [Phys. Rev. D68 (2003) 084004] and re-solve the problem using the anisotropic formalism. We find that the results are different and this difference occurs due to the fact that the boundary condition of the anisotropic formalism is not correct, leading to an inconsistent physical situation.

In this paper, model of gravitational collapse of anisotropic compact stars in a new theory of $f(R)$ gravity has been developed. The author considers the modified gravity model of $f(R)=\xi R^4$ to investigate a physically acceptable model of gravitational collapse of anisotropic compact stars. First, the author presents a brief review of the development of field equations of gravitational collapse in $f(R)$ gravity for a particular interior metric for compact stars. Then analytical solutions for various physical quantities of collapsing anisotropic compact stars in $\xi R^4$ gravity have been developed. By analyzing plots of various physical parameters and conditions, it is shown that the model is physically acceptable for describing the gravitational collapse of anisotropic compact stars in $f(R)=\xi R^4$ gravity.

In this study, we have explored an anisotropic stellar configuration by applying the Karmarkar condition in the framework of $F(T,{𝒯})$ [where $T$ and ${𝒯}$ stand for torsion and trace of energy–momentum tensor (EMT)] gravity. We have developed field equations of $F(T,{𝒯})$ gravity for a spherically symmetric line element and considered a viable $F(T,{𝒯})$ model, i.e. $F(T,{𝒯})=\alpha T{(r)}^2+\beta {𝒯}(r)$ (where $\alpha$ and $\beta$ are arbitrary constants) for meaningful results. Following [S. K. Maurya, B. S. Ratanpal and M. Govender, Ann. Phys.382 (2017) 36], a spherically symmetric solution of embedding class I has been explored which resulted into a generalized compact stellar model. For the evaluation of unknown parameters, we use the matching conditions at the boundary by taking spherical space-time metric as interior and Schwarzschild space-time solution as exterior space-time metric. The viability of our proposed model is checked by exploring the nature of thermodynamical variables ($\rho$, $p_r$, $p_t$), anisotropy, energy condition, Tolman–Oppenheimer–Volkov (TOV) forces, Abreu condition, equation of state parameters and adiabatic index taking the observational data of different compact stars like PSR J1416-2230, 4U 1608-52, Cen X-3, EXO 1785-248 and SMC X-1. Our stellar model is found.

This paper examines the viable characteristics of anisotropic compact stars in $f(\Re ,T^2)$ theory ($\Re$ is the Ricci scalar and $T^2=T_{\alpha \beta }{T}^{\alpha \beta }$). In this perspective, we use Tolman–Kuchowicz solutions $(\mu =w{r}^2+2lnz$ and $\nu =ln(1+x{r}^2+y{r}^4))$ to examine the configurations of static spherically symmetric structures. The unknown constants are found by the first fundamental form of Darmois junction conditions. We analyze the behavior of fluid parameters in the interior of 4U 1538-52, PSRJ 1614-220, EXO 1785-248 and SAXJ 1808.4-3658 compact stars correspond to different models of this theory. Furthermore, the stability of the proposed compact stellar objects is examined through sound speed and adiabatic index methods. The satisfaction of requisite conditions ensures that stable compact objects exist in this framework.