Effects of mirror dark matter on neutron stars

TL;DR

This paper explores how mirror dark matter, if present in neutron stars, alters their mass-radius relation and critical mass for collapse, with potential observational signatures and implications for neutron star formation.

Contribution

It introduces a generalized hydrostatic model for neutron stars with multiple fluids and demonstrates how mirror baryons significantly affect their structure and evolution.

Findings

Mirror baryons modify the neutron star mass-radius relation.

Presence of mirror baryons lowers the critical mass for core collapse.

Neutron stars with mirror dark matter could be more compact and have lower masses.

Abstract

If dark matter is made of mirror baryons, they are present in all gravitationally bound structures. Here we investigate some effects of mirror dark matter on neutron stars and discuss possible observational consequences. The general-relativistic hydrostatic equations are generalized to spherical objects with multiple fluids that interact by gravity. We use the minimal parity-symmetric extension of the standard model, which implies that the microphysics is the same in the two sectors. We find that the mass-radius relation is significantly modified in the presence of a few percent mirror baryons. This effect mimics that of other exotica, e.g., quark matter. In contrast to the common view that the neutron-star equilibrium sequence is unique, we show that it depends on the relative number of mirror baryons to ordinary baryons. It is therefore history dependent. The critical mass for core collapse, i.e., the process by which neutron stars are created, is modified in the presence of mirror baryons. We calculate the modified Chandrasekhar mass and fit it with a polynomial. A few percent mirror baryons is sufficient to lower the critical mass for core collapse by ~0.1 M_sun. This could allow for the formation of extraordinary compact neutron stars with low mass.