Interpreting Mass and Radius Measurements of Neutron Stars with Dark Matter Halos

TL;DR

This paper investigates how dark matter halos around neutron stars influence X-ray observations, potentially affecting mass and radius measurements and offering new insights into dark matter properties.

Contribution

It introduces a numerical simulation of dark matter admixed neutron stars with halos, analyzing their impact on X-ray pulse profiles and implications for interpreting observational data.

Findings

Dark matter halos cause significant deviations in X-ray flux profiles.

Different dark matter models produce distinct halo structures affecting observations.

Misinterpretation of neutron star properties can occur if dark halos are not considered.

Abstract

The high densities of neutron stars (NSs) could provide astrophysical locations for dark matter (DM) to accumulate. Depending on the DM model, these DM admixed NSs (DANSs) could have significantly different properties than pure baryonic NSs, accessible through X-ray observations of rotation-powered pulsars. We adopt the two-fluid formalism in general relativity to numerically simulate stable configurations of DANSs, assuming a fermionic equation of state (EOS) for the DM with repulsive self-interaction. The distribution of DM in the DANS as a halo affects the path of X-rays emitted from hot spots on the visible baryonic surface causing notable changes in the pulse profile observed by telescopes such as NICER, compared to pure baryonic NSs. We explore how various DM models affect the DM mass distribution, leading to different types of dark halos. We quantify the deviation in observed X-ray flux from stars with each of these halos. We identify the pitfalls in interpreting mass and radius measurements of NSs inferred from electromagnetic radiation and constraining the baryonic matter EOS, if these dark halos exist.