Numerical models for stationary superfluid neutron stars in general relativity with realistic equations of state

TL;DR

This paper develops a comprehensive numerical model for rotating superfluid neutron stars in general relativity, incorporating realistic microphysics and entrainment effects, to better understand their structure and properties.

Contribution

It introduces a novel fully relativistic framework for modeling superfluid neutron stars with realistic equations of state and entrainment, extending previous formalisms.

Findings

Accurate equilibrium configurations for superfluid neutron stars were obtained.

Entrainment significantly affects density profiles and moments of inertia.

Results agree with Fermi liquid theory in the small velocity limit.

Abstract

We present a numerical model for uniformly rotating superfluid neutron stars, for the first time with realistic microphysics including entrainment, in a fully general relativistic framework. We compute stationary and axisymmetric configurations of neutron stars composed of two fluids, namely superfluid neutrons and charged particles (protons and electrons), rotating with different rates around a common axis. Both fluids are coupled by entrainment, a non-dissipative interaction which in case of a non-vanishing relative velocity between the fluids, causes the fluid momenta being not aligned with the respective fluid velocities. We extend the formalism by Comer and Joynt (2003) in order to calculate the equation of state (EoS) and entrainment parameters for an arbitrary relative velocity. The resulting entrainment matrix fulfills all necessary sum rules and in the limit of small relative velocity our results agree with Fermi liquid theory ones, derived to lowest order in the velocity. This formalism is applied to two new nuclear equations of state which are implemented in the numerical model. We are able to obtain precise equilibrium configurations. Resulting density profiles and moments of inertia are discussed employing both EoSs, showing the impact of entrainment and the dependence on the EoS.