Slowly rotating superfluid neutron stars with isospin dependent entrainment in a two-fluid model

TL;DR

This paper models slowly rotating superfluid neutron stars using a relativistic two-fluid approach, incorporating isospin-dependent entrainment effects via a relativistic mean field theory, and examines how these influence stellar properties like mass and rotation limits.

Contribution

It introduces a detailed relativistic two-fluid model with isospin-dependent entrainment for superfluid neutron stars, including the effects of $ ho$ mesons on global properties.

Findings

Entrainment affects the mass and shape of neutron stars.

The Kepler limit is modified by isospin-dependent entrainment.

Including $ ho$ mesons alters the star's rotational properties.

Abstract

We investigate the slowly rotating general relativistic superfluid neutron stars including the entrainment effect in a two-fluid model, where one fluid represents the superfluid neutrons and the other is the charge-neutral fluid called the proton fluid, made of protons and electrons. The equation of state and the entrainment effect between the superfluid neutrons and the proton fluid are computed using a relativistic mean field (RMF) model where baryon-baryon interaction is mediated by the exchange of $\sigma$, $\omega$, and $\rho$ mesons and scalar self interactions are also included. The equations governing rotating neutron stars in the slow rotation approximation are second order in rotational velocities of neutron and proton fluids. We explore the effects of the isospin dependent entrainment and the relative rotation between two fluids on the global properties of rotating superfluid neutron stars such as mass, shape, and the mass shedding (Kepler) limit within the RMF model with different parameter sets. It is observed that for the global properties of rotating superfluid neutron stars in particular, the Kepler limit is modified compared with the case that does not include the contribution of $\rho$ mesons in the entrainment effect.