Possible Supermassive Dark Object Composed of Light Fermionic Gas with an Embedded Neutron Star Core

Abstract

The structure of dark matter admixed neutron stars (DANSs) are investigated, adopting a non-annihilating self-interacting fermionic dark matter (DM) model, with a particular focus on the case of the light DM particle mass $m_D\in [10^{-10},1]$ GeV. The DANSs become DM-dominated configurations when $m_D<10^{-1}$ GeV, where a compact neutron star core becomes embedded within an extremely large DM halo. It is found that the maximum mass of DANSs is inversely proportional to $m_D$, approximately as $0.627(GeV/m_{\mathrm{D}}{)}^2{\mathrm{M}}_{\odot }$, which implies that extremely large masses can be achieved for small $m_{\mathrm{D}}$. For $m_D\sim 5\times 10^{-4}$ GeV, the calculated mass and size of the DM halo can be comparable to those of supermassive black holes such as Sgr A*. Our findings hint at a scenario where neutron stars might serve as strong gravitational seeds for such supermassive dark objects.