Finch–Skea compact stellar configurations in Rastall gravity: structure, stability, and physical admissibility

Abstract

We construct static, anisotropic compact-star configurations in Rastall gravity using the Finch–Skea metric ansatz and investigate how the Rastall coupling modifies the structure and stability of ultra-dense matter. We systematically analyze the dependence of the energy density, pressures, anisotropy, compactness, and gravitational redshift on the Rastall parameter, with the general relativity (GR) limit recovered when the coupling vanishes. The resulting mass–radius and moment of inertia–mass relations show that the Rastall modification can increase both the maximum mass and the corresponding moment of inertia relative to the GR configurations. We further compare the predicted maximum mass and moment of inertia with the observational constraints for neutron-star candidates, including PSR J0437–4715, PSR J2222–0137, and PSR J0348+0432, and examine the extent to which the model accommodates the corresponding astrophysically inferred properties. The physical admissibility of the configurations is assessed through the standard energy conditions, causality, the adiabatic-index criterion, the generalized Tolman–Oppenheimer–Volkoff equilibrium equation, and the Herrera cracking condition. Our results indicate that the Rastall coupling provides a systematic modification of the maximum mass, compactness, and rotational properties of anisotropic compact stars while preserving the required physical and stability conditions over the parameter range considered. These results demonstrate that Rastall gravity can provide a viable modified-gravity framework for exploring the structure of ultra-dense compact objects beyond general relativity.