Pure Gravitational Wave Estimation of Hubble's Constant using Neutron Star-Black Hole Mergers

TL;DR

This paper introduces a novel method to estimate Hubble's constant solely from gravitational wave data of neutron star-black hole mergers, avoiding electromagnetic observations and expanding the redshift range.

Contribution

It presents a new purely gravitational wave-based approach to determine Hubble's constant using NSBH mergers, without relying on afterglow detection.

Findings

Initial estimate of H_0 = 86^{+55}_{-46} km/s/Mpc from two NSBH events.

Forecasted that 10 more NSBH events can achieve ~20% precision in H_0 measurement.

Method works within redshift z<0.25 with current GW sensitivity.

Abstract

Here we show how $H_0$ can be derived purely from the gravitational waves (GW) of neutron star-black hole (NSBH) mergers. This new method provides an estimate of $H_0$ spanning the redshift range, $z<0.25$ with current GW sensitivity and without the need for any afterglow detection. We utilise the inherently tight neutron star mass function together with the NSBH waveform amplitude and frequency to estimate distance and redshift respectively, thereby obtaining $H_0$ statistically. Our first estimate is $H_0 = 86^{+55}_{-46}$ km s$^{-1}$ Mpc$^{-1}$ for the secure NSBH events GW190426 and GW200115. We forecast that soon, with 10 more such NSBH events we can reach competitive precision of $\delta H_0/H_0 \lesssim 20\%$.