STUDY OF DARK-MATTER ADMIXED NEUTRON STARS USING THE EQUATION OF STATE FROM THE ROTATIONAL CURVES OF GALAXIES

ABSTRACT In this work, we employ the dark matter equations of state (DMEOSs) obtained from the rotational curves of galaxies as well as the fermionic DMEOS with to study the structure of dark-matter admixed neutron stars (DMANSs). Applying the equation of state in the Skyrme framework for the neutron matter (NM), we calculate the mass-radius relation for different DMANSs with various DMEOSs and central pressure of dark matter (DM) to NM ratios. Our results show that for some DMEOSs, the mass-radius relations are in agreement with new observations, e.g., EXO 1745-248, 4U 1608-52, and 4U 1820-30, which are inconsistent with normal neutron stars. We conclude that both DMEOSs and central pressure ratios of DM to NM affect the slope of the mass-radius relation of DMANSs. This is because of the interaction between DM and NM, which leads to gravitationally or self-bound DMANSs. We study the radius of the NM sphere as well as the radius of the DM halo for different DMANSs. The results confirm that, in some cases, a NM sphere with a small radius is surrounded by a halo of DM with a larger radius. Our calculations verify that, due to the different degrees of DM domination in DMANSs, with a value of the visible radius of a star two possible DMANSs with different masses can exist. The gravitational redshift is also calculated for DMANSs with different DMEOSs and central pressure ratios. The results explain that the existence of DM in a DMANS leads to higher values of gravitational redshift of the star.