Rotating neutron stars in the first-order post-Newtonian approximation

Abstract

We study models of uniformly and differentially rotating neutron stars in the framework of the first-order post-Newtonian approximation in general relativity as established by Chandrasekhar. In particular, we adopt the polytropic equation of state in order to derive the appropriate hydrodynamic equations and a rotation law based on the generalized Clement’s model. To compute equilibrium configurations at the mass-shedding limit, i.e. at critical angular velocity (equivalently, Keplerian angular velocity), we develop an iterative numerical method, belonging to the category of the well-known “self-consistent field methods”, with two perturbation parameters: the “rotation parameter” ῡ and the “gravitation or relativity parameter” σ̄. These two parameters represent the effects of rotation and gravity on the configuration. We investigate the validity and the limits of our method by comparing our results with respective results of other computational methods and public domain codes. As it turns out, our method can derive satisfactory results for general-relativistic polytropic configurations at critical rotation.