Possible Implications of Asymmetric Fermionic Dark Matter for Neutron Stars

TL;DR

This paper explores how asymmetric fermionic dark matter could influence neutron star properties, showing that mixed stars with dark fermions can surpass the mass limits of ordinary neutron stars under certain conditions.

Contribution

It introduces a combined Newtonian and relativistic analysis of mixed neutron stars with dark fermions, highlighting potential mass increases due to dark matter inclusion.

Findings

Mixed neutron stars can reach higher masses than pure neutron stars.

Dark fermion mass less than baryon mass enables larger maximum star mass.

Results apply to various dark matter models, including mirror matter and self-interacting fermions.

Abstract

We consider the implications of fermionic asymmetric dark matter for a "mixed neutron star" composed of ordinary baryons and dark fermions. We find examples, where for a certain range of dark fermion mass -- when it is less than that of ordinary baryons -- such systems can reach higher masses than the maximal values allowed for ordinary ("pure") neutron stars. This is shown both within a simplified, heuristic Newtonian analytic framework with non-interacting particles and via a general relativistic numerical calculation, under certain assumptions for the dark matter equation of state. Our work applies to various dark fermion models such as mirror matter models and to other models where the dark fermions have self interactions.