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

Abstract: We thoroughly investigate the scenario where dark matter is admixed with the ordinary nuclear matter in a neutron star, focusing on the finite temperature Bose-Einstein condensate (BEC) as the dark matter candidate. These hybrid configurations yield masses and radii that match observed values of pulsar mass-radius observation and adhere to dimensionless tidal Love number constraints from the binary neutron star merger event GW170817. By analyzing possible, stable mass-radius configurations and the dimensionless tidal Love number constraints, we determine the dark matter content in a nuclear matter whose masses and radii comply with these astrophysical limits. We perform our analyses with three models for the ordinary nuclear matter equation of state (EoS), APR4, MPA1, and SLy. Our analyses suggest that if APR4 is the correct nuclear matter EoS governing neutron stars in the Universe, and the components of this event were indeed dark matter admixed neutron stars, then the most likely dark matter fractions in their cores are approximately 5.65% and 7.97%, respectively. In contrast, for the other two EoSs considered, the predicted dark matter fractions are significantly higher, exceeding 12%. We also consider finite temperature BEC stars. We find that temperature has negligible effect on the stability criteria or tidal properties of these dark matter admixed neutron stars.