Effects of dark matter on the in-spiral properties of the binary neutron stars

Abstract

ABSTRACT Using the relativistic mean-field model, we calculate the properties of binary neutron star (BNS) in the in-spiral phase. Assuming the dark matter (DM) particles are accreted inside the neutron star (NS) due to its enormous gravitational field, the mass M, radius R, tidal deformability λ, and dimensionless tidal deformability Λ are calculated at different DM fractions. The value of M, R, λ, and Λ decreases with the increase of DM percentage inside the NS. The in-spiral phase properties of the BNS are explored within the post-Newtonian (PN) formalism, as it is suitable up to the last orbits in the in-spiral phase. We calculate the strain amplitude of the polarization waveform h+ and h×, (2,2) mode waveform h22, orbital phase Φ, frequency of the gravitational wave f, and PN parameter x with DM as an extra candidate inside the NS. The magnitude of f, Φ, and x are almost the same for all assumed forces; however, the in-spiral time duration in the last orbit is different. We find that the BNS with soft equation of state and a high fraction of DM sustains more time in their in-spiral phase. We suggest that one should take DM inside the NS when they modelling the in-spiral waveforms for the BNS systems.