A new estimation method for mass of an isolated neutron star using gravitational waves

TL;DR

This paper proposes a novel method to estimate the mass of an isolated neutron star by analyzing the gravitational wave phase shifts caused by the star's gravitational potential, demonstrating feasibility with simulations.

Contribution

It introduces a new approach utilizing phase shifts in continuous gravitational waves to measure neutron star mass, which has not been previously explored.

Findings

Mass can be estimated with about 20% accuracy at 1 kpc distance.

The method is effective for neutron stars with ellipticity of 10^{-6}.

Feasibility shown using Monte Carlo simulations with Einstein Telescope.

Abstract

We investigate a possibility of estimating mass of an isolated rapidly rotating neutron star (NS) from a continuous gravitational wave (GW) signal emitted by the NS. When the GW passes through the gravitational potential of the NS, the GW takes a slightly longer time to travel to an observer than it does in the absence of the NS. Such a time dilation effect holds also for photons and is often referred to as the gravitational time delay (or the Shapiro time delay). Correspondingly, the phase of the GW from the NS shifts due to the Coulomb type gravitational potential of the NS, and the resulting logarithmic phase shift depends on the mass, the spin frequency of the NS, and the distance to the NS. We show that the NS mass can, in principle, be obtained by making use of the phase shift difference between two modes of the continuous GW such as once and twice spin frequency modes induced by a freely precessing NS or a NS containing a pinned superfluid core. We estimate the measurement accuracy of the NS mass using Monte Carlo simulations and find that the mass of the NS with its ellipticity $10^{-6}$ at 1 kpc is typically measurable with an accuracy $20%$ using Einstein Telescope.