Static and slowly rotating neutron stars in scalar-tensor theory with self-interacting massive scalar field

Decoupled Embedding Class-One Strange Stars in Self-Interacting Brans–Dicke Gravity

This work aims to extend two isotropic solutions to the anisotropic domain by decoupling the field equations in self-interacting Brans–Dicke theory. The extended solutions are obtained by incorporating an additional source in the isotropic fluid distribution. We deform the radial metric potential to disintegrate the system of field equations into two sets such that each set corresponds to only one source (either isotropic or additional). The system related to the anisotropic source is solved by employing the MIT bag model as an equation of state. Further, we develop two isotropic solutions by plugging well-behaved radial metric potentials in Karmarkar’s embedding condition. The junction conditions at the surface of the star are imposed to specify the unknown constants appearing in the solution. We examine different physical characteristics of the constructed quark star models by using the mass and radius of PSR J1903+327. It is concluded that, in the presence of a massive scalar field, both stellar structures are well-behaved, viable and stable for smaller values of the decoupling parameter.

Structure of Neutron Stars in Massive Scalar-Tensor Gravity

We compute families of spherically symmetric neutron-star models in two-derivative scalar-tensor theories of gravity with a massive scalar field. The numerical approach we present allows us to compute the resulting spacetimes out to infinite radius using a relaxation algorithm on a compactified grid. We discuss the structure of the weakly and strongly scalarized branches of neutron-star models thus obtained and their dependence on the linear and quadratic coupling parameters α0, β0 between the scalar and tensor sectors of the theory, as well as the scalar mass μ. For highly negative values of β0, we encounter configurations resembling a “gravitational atom”, consisting of a highly compact baryon star surrounded by a scalar cloud. A stability analysis based on binding-energy calculations suggests that these configurations are unstable and we expect them to migrate to models with radially decreasing baryon density and scalar field strength.

Quark Stars in Massive Brans–Dicke Gravity with Tolman–Kuchowicz Spacetime

In this paper, we construct anisotropic model representing salient features of strange stars in the framework of massive Brans–Dicke gravity. We formulate the field equations for Tolman–Kuchowicz ansatz by incorporating the MIT bag model. Junction conditions are applied on the boundary of the stellar model to evaluate the unknown constants in terms of mass and radius of the star. The radius of the strange star candidate PSR J1614-2230 is predicted by assuming maximum anisotropy at the surface of the star for different values of the coupling parameter, mass of the scalar field and bag constant. We examine various properties as well as the viability and stability of the anisotropic sphere. We conclude that the astrophysical model agrees with the essential criteria of a physically realistic model for higher values of the coupling parameter as well as mass of the scalar field.