Evolution of Neutron Star Environment in the Galactic Halo : Implications for Dark Matter Accretion

Abstract

Neutron stars (NS) are one of the indirect detection probes for dark matter (DM). The presence of DM is known to affect the observable properties of NS. Theoretical calculations for various equations of state of a DM admixed NS lead to estimates of the DM mass in a NS of the order of $10^{-2} M_{\odot}$. On the other hand, simplistic estimates of the amount of DM that is accreted on to the NS in the Solar neighborhood, over its age, suggest that this number is of the order $10^{-14} M_{\odot}$. Various studies have addressed this non-agreement theoretically by explaining the mechanisms leading to higher fraction than expected from smooth spherically symmetric accretion. In this work, we attempt to assess the role of the dynamic DM environmental density in the Galactic halo to explain possible enhancement in DM accretion. We consider a high resolution N-body simulation and method of Voronoi tessellation to calculate local DM density around putative NS locations in a statistically representative sample of Milky Way analogues. We infer that the dynamics of substructure may enhance the DM mass in NS by about a factor 2 as compared to the baseline, spherically symmetric expectation. Environmental effects therefore cannot explain the orders of magnitude discrepancy between equation of state and accretion based estimates of DM admixed in NS.