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

TL;DR

This study investigates how dark matter accreted inside neutron stars affects their physical properties and the gravitational wave signals during binary neutron star in-spiral, highlighting the importance of including dark matter in waveform modeling.

Contribution

It introduces a model incorporating dark matter inside neutron stars and analyzes its impact on in-spiral gravitational wave properties using relativistic mean-field and post-Newtonian formalisms.

Findings

Mass, radius, and deformability decrease with more dark matter.

In-spiral duration is longer for neutron stars with high dark matter fractions.

Dark matter presence influences gravitational wave frequency and phase evolution.

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 $\lambda$ and dimensionless tidal deformability $\Lambda$ are calculated at different DM fractions. The value of $M$, $R$, $\lambda$ and $\Lambda$ 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 $h_\times$, (2,2) mode waveform $h_{22}$, orbital phase $\Phi$, frequency of the gravitational wave $f$ and PN parameter $x$ with DM as an extra candidate inside the NS. The magnitude of $f$, $\Phi$ 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.