Minimally deformed anisotropic stars by gravitational decoupling in Einstein–Gauss–Bonnet gravity

In this article, we develop a theoretical framework to study compact stars in Einstein gravity with the Gauss–Bonnet (GB) combination of quadratic curvature terms. We mainly analyzed the dependence of the physical properties of these compact stars on the Gauss–Bonnet coupling strength. This work is motivated by the relations that appear in the framework of the minimal geometric deformation approach to gravitational decoupling (MGD-decoupling), we establish an exact anisotropic version of the interior solution in Einstein–Gauss–Bonnet gravity. In fact, we specify a particular form for gravitational potentials in the MGD approach that helps us to determine the decoupling sector completely and ensure regularity in interior space-time. The interior solutions have been (smoothly) joined with the Boulware–Deser exterior solution for 5D space-time. In particular, two different solutions have been reported which comply with the physically acceptable criteria: one is the mimic constraint for the pressure and the other approach is the mimic constraint for density. We present our solution both analytically and graphically in detail.

Anisotropic stars via embedding approach in Brans–Dicke gravity

In the present article, the solution of the Einstein–Maxwell field equations in the presence of a massive scalar field under the Brans-Dicke (BD) gravity is obtained via embedding approach, which describes a charged anisotropic strange star model. The interior spacetime is described by a spherically symmetric static metric of embedding class I. This reduces the problem to a single-generating function of the metric potential which is chosen by appealing to physics based on regularity at each interior point of the stellar interior. The resulting model is subjected to rigorous physical checks based on stability, causality and regularity for particular object PSR J1903+327. We also show that our solutions describe compact objects such as PSR J1903+327; Cen X-3; EXO 1785-248 and LMC X-4 to an excellent approximation. Novel results of our investigation reveal that the scalar field leads to higher surface charge densities which in turn affects the compactness and upper and lower values imposed by the modified Buchdahl limit for charged stars. Our results also show that the electric field and scalar field which originate from entirely different sources couple to alter physical characteristics such as mass-radius relation and surface redshift of compact objects. This superposition of the electric and scalar fields is enhanced by an increase in the BD coupling constant, $$\omega _{BD}$$ ω BD .

Modelling of a compact anisotropic star as an anisotropic fluid sphere in f(T) gravity

In this article, the authors have discussed a new exact model of anisotropic stars in the f(T) theory of gravity. A parametric form of the metric functions has been implemented to solve the dynamical equations in f(T) theory with the anisotropic fluid. The novelty of the work is that the obtained solutions do not contain singularity but are potentially stable. The estimated values for mass and radius of the different strange stars, RX J 1856–37, Her X-1, and Vela X-12, have been utilized to find the values of unknown constants in Krori and Barua metrics. The physical parameters like anisotropy, stability, and redshift of the stars have been examined in detail.