Effects from dark matter halos on x-ray pulsar pulse profiles

Neutron stars (NSs) can capture dark matter (DM) particles because of their deep gravitational potential and high density. The accumulated DM can affect the properties of NSs. In this work we use a general relativistic two-fluid formalism to solve the structure of DM-admixed NSs (DANSs) and the surrounding spacetime. Specifically, we pay attention to the situation where those DANSs possess DM halos. Due to the gravitational effect of the DM halo, the pulse profile of an x-ray pulsar is changed. Our study finds a universal relation between the peak flux deviation of the pulse profile and ${M}_{\mathrm{halo}}/{R}_{\mathrm{BM}}$, which is the ratio of the DM halo mass, ${M}_{\mathrm{halo}}$, to the baryonic matter (BM) core radius, ${R}_{\mathrm{BM}}$. Our results show that, when ${M}_{\mathrm{halo}}/{R}_{\mathrm{BM}}=0.292$ and the DM particle mass ${m}_{f}=0.3\text{ }\text{ }\mathrm{GeV}$, the maximum deviation of the profile can be larger than 100%, which has implications in x-ray pulsar observation.