Bose-Einstein Condensate Dark Matter in the Core of Neutron Stars: Implications for Gravitational-wave Observations

TL;DR

This paper explores how a finite-temperature Bose-Einstein condensate dark matter component within neutron stars affects their structure and gravitational wave signals, providing insights into dark matter's role in dense astrophysical objects.

Contribution

It introduces a relativistic two-fluid model for neutron stars with BEC dark matter, analyzing its impact on mass, radius, and tidal deformability, and compares predictions with gravitational wave data.

Findings

Dark matter reduces maximum neutron star mass and radius.

Presence of dark matter alters tidal deformability and mass-$ ext{Lambda}$ relations.

Moderate temperature effects are negligible for stability and tidal properties.

Abstract

We investigate neutron stars admixed with dark matter (DM) in the form of a finite-temperature Bos-Einstein condensate (BEC) within a general relativistic two-fluid framework in which the nuclear and dark components interact only gravitationally. Using realistic nuclear matter equations of state (EOS), APR4, MPA1, and SLy, we construct equilibrium configurations and compute mas-radius relations, tidal Love numbers, and dimensionless tidal deformabilities. We quantify how the presence of a BEC dark component modifies the mas-$\Lambda$ relation relevant for gravitational wave observations, finding that increasing the DM mass fraction generically reduces the maximum mass, radius, and tidal deformability of neutron stars. By comparing theoretical mass-$\Lambda$ curves with EOS-insensitive posteriors from GW170817, we evaluate, in a conditional sense, the dark matter fractions that would align a given nuclear EOS with the observed tidal constraints; for example, under the assumption that APR4 describes nuclear matter and that the GW170817 components were dark-matter admixed neutron stars, our study favors dark matter fractions of order a few percent, whereas stiffer EOSs require larger fractions to achieve comparable agreement. This interpretation assumes that inspiral waveforms are adequately characterized by tidal deformability and should therefore be regarded as structural rather than a direct detection of dark matter. We also examine finite-temperature effects in the BEC sector and find that, for moderate dark matter fractions, temperature has a negligible impact on the stability and tidal properties of admixed configurations. Our results demonstrate how even modest DM admixtures can influence neutron star structure and tidal observables, highlighting the importance of considering non-standard matter components in multimessenger constraints on dense matter.