Precise peculiar velocities from gravitational waves accompanied by electromagnetic signals and cosmological applications

TL;DR

This paper introduces a new method to measure peculiar velocities using gravitational wave signals and electromagnetic counterparts, significantly improving precision and enabling cosmological tests like measuring the Hubble constant and growth rate of structure.

Contribution

The paper proposes a novel approach to determine peculiar velocities directly from gravitational wave and electromagnetic observations, reducing uncertainties compared to traditional methods.

Findings

Peculiar velocity uncertainties can be reduced to 10 km/s at 100 Mpc.

Using dozens of GW events, the Hubble constant can be measured with 0.5% precision.

The growth rate of structure can be determined with 0.6% accuracy.

Abstract

Peculiar velocities are a precious tool to study the large-scale distribution of matter in the local universe and test cosmological models. However, present measurements of peculiar velocities are based on empirical distance indicators, which introduce large error bars. Here we present a new method to measure the peculiar velocities, by directly estimating luminosity distances through waveform signals from inspiralling compact binaries and measuring redshifts from electromagnetic (EM) counterparts. In the future, with the distance uncertainty of GW events reducing to $0.1$ per cent by future GW detectors, the uncertainty of the peculiar velocity can be reduced to $10$ km/s at 100 mega parsecs. We find that dozens of GW events with EM counterparts can provide a Hubble constant $H_0$ uncertainty of $0.5\%$ and the growth rate of structure with a $0.6\%$ precision in the third-generation ground-base GW detectors, which can reconcile the $H_0$ tension and determine the origins for cosmic accelerated expansion.