Dark matter admixed neutron stars

TL;DR

This paper investigates how dark matter, modeled as either a free Fermi gas or mirror dark matter, affects the structure and stability of neutron stars by solving multi-fluid TOV equations and analyzing oscillation modes.

Contribution

It provides a comprehensive stability analysis of dark matter admixed neutron stars using two different methods and explores their oscillation frequencies across parameter space.

Findings

Dark matter influences neutron star mass and radius.

Stable configurations are identified across parameter space.

Radial oscillation frequencies are computed for various models.

Abstract

Neutron stars could contain a mixture of ordinary nuclear matter and dark matter, such that dark matter could influence observable properties of the star, such as its mass and radius. We study these dark matter admixed neutron stars for two choices of dark matter: a free Fermi gas and mirror dark matter. In addition to solving the multi-fluid Tolman-Oppenheimer-Volkoff equations for static solutions and presenting mass-radius diagrams, we focus on two computations that are lacking in the literature. The first is a rigorous determination of stability over the whole of parameter space, which we do using two different methods. The first method is based on harmonic time-dependent perturbations to the static solutions and on solving for the radial oscillation frequency. The second method, which is less well-known, conveniently makes use of unperturbed, static solutions only. The second computation is of the radial oscillation frequency, for fundamental modes, over large swaths of parameter space.