Impact of Dark Matter On the Properties of Static and Rotating Neutron Star

Abstract

This research explores the combined effects of dark matter (DM) and rotation on the structural and dynamical properties of neutron stars (NSs). Utilizing a self-interacting dark matter model inspired by the neutron decay anomaly, the study integrates DM within the relativistic mean-field (RMF) framework, modeling static and rotating NSs to observe the impact of varying DM interaction strengths and angular velocities. The HartleThorne formalism is employed to model rotating stars, examining key properties, including mass, radius, central energy density, and eccentricity, across a range of DM and rotation conditions. Results reveal that DM significantly influences the neutron star’s equation of state (EOS), generally softening it and reducing the star’s mass and radius. In contrast, rotational effects increase mass and radius due to centrifugal forces. Higher DM fractions reduce the NS’s eccentricity, indicating less deformation from rotation compared to DM-free stars. Additionally, variations in the DM interaction strength alter the star’s massshedding limit, with low DM fractions allowing higher rotational speeds before mass-shedding occurs, thus supporting larger mass and radii under rotation. For fixed DM fractions, high angular velocities lead to positive deviations in mass and radius from the baseline (DM-free) values, indicating enhanced deformation, while low angular velocities result in reduced mass and radius due to DM’s influence. By comparing DM-admixed and DM-free models, the study also examines the relative deviations in maximum rotational mass and equatorial radius, showing that both DM and rotation substantially modify these properties. The findings underscore the interplay between DM content and rotation in defining NS characteristics, offering insights for interpreting observations of highly dense, rotating astrophysical objects. The results align well with current observational constraints, including NICER and XMM-Newton data, providing an avenue for future studies on DM’s role in the behavior of ultra-dense matter within NSs.