Study of Dark-Matter Admixed Neutron Stars using the Equation of State from the Rotational Curves of Galaxies

Z. Rezaei

Published 2016-12-08Version 1

In this work, we employ the dark matter equations of state (DMEOSs) obtained from the rotation curves of galaxies as well as the fermionic DMEOS with m = 1.0 GeV to study the structure of dark matter admixed neutron stars (DMANSs). Applying the equation of state in the Skyrme framework for the neutron matter, we calculate the mass-radius relation for different DMANSs with various DMEOSs and central pressure of dark matter to neutron matter ratios. Our results show that for some DMEOSs, the mass-radius relations are in agreement with the new observations, e.g. EXO 1745-248, 4U 1608-52, and 4U 1820-30, which are inconsistent with the normal neutron stars. We conclude that both DMEOS and central pressure ratio of dark matter to neutron matter affect the slope of the mass-radius relation of DMANS. This is because of the interaction between dark matter and neutron matter which leads to gravitationally or self bound DMANSs. We study the radius of the neutron matter sphere as well as the radius of the dark matter halo for different DMANSs. The results confirm that in some cases, the neutron matter sphere with a small radius is surrounded by a halo of dark matter having a larger radius. Our calculations verify that due to the different degrees of dark matter domination in DMANSs, with a value of the visible radius of star two possible DMANSs with different masses can be exist. The gravitational redshift is also calculated for DMANSs with different DMEOSs and central pressure ratios. The results explain that the existence of dark matter in the DMANS leads to higher values for the gravitational redshift of the star.