Stability of Neutron-Dark Matter Mixed Stars and Hybrid Stars

TL;DR

This paper establishes the equivalence of two methods for analyzing the stability of mixed neutron-dark matter stars, revealing a stability boundary and stable configurations that can inform astrophysical observations and dark matter constraints.

Contribution

It proves the equivalence of two stability determination methods for multi-fluid stars and characterizes the stability boundary for dark matter admixed neutron stars.

Findings

Stable mixed star configurations form a surface in parameter space.

Existence of twin stars with identical mass and radius but different structures.

A distinct stability boundary from single-fluid models.

Abstract

Concerning the stability of two-fluid star models, we prove the rigorous equivalence of two independent determining methods for mixed stars, after a brief review of the hybrid star case. Our derivations apply to general multi-fluid cases, and here we take dark matter admixed neutron star models for example, demonstrating a stability boundary distinct from the single-fluid case. Stable configurations form a surface in the three-dimensional parameter space of (either) central pressure, mass, and radius, which yields a group containing stable mixed stars. This group includes twin stars with identical masses and radii but different interior structures. These results can help interpret compact star observations and constrain dark matter properties through astrophysics.