Determining the Hubble constant from gravitational wave observations of merging compact binaries

TL;DR

This paper discusses how combined gravitational wave and electromagnetic observations of neutron star mergers can precisely measure the Hubble constant independently of traditional methods, reducing systematic uncertainties.

Contribution

It demonstrates that multi-messenger observations of neutron star mergers can accurately determine the Hubble constant without relying on the cosmic distance ladder.

Findings

15 events yield 5% H_0 measurement precision

30 events constrain H_0 to better than 1%

Non-Gaussian posteriors improve overall measurement accuracy

Abstract

Recent observations have accumulated compelling evidence that some short gamma-ray bursts (SGRBs) are associated with the mergers of neutron star (NS) binaries. This would indicate that the SGRB event is associated with a gravitational-wave (GW) signal corresponding to the final inspiral of the compact binary. In addition, the radioactive decay of elements produced in NS binary mergers may result in transients visible in the optical and infrared with peak luminosities on hours-days timescales. Simultaneous observations of the inspiral GWs and signatures in the electromagnetic band may allow us to directly and independently determine both the luminosity distance and redshift to a binary. These standard sirens (the GW analog of standard candles) have the potential to provide an accurate measurement of the low-redshift Hubble flow. In addition, these systems are absolutely calibrated by general relativity, and therefore do not experience the same set of astrophysical systematics found in traditional standard candles, nor do the measurements rely on a distance ladder. We show that 15 observable GW and EM events should allow the Hubble constant to be measured with 5% precision using a network of detectors that includes advanced LIGO and Virgo. Measuring 30 beamed GW-SGRB events could constrain H_0 to better than 1%. When comparing to standard Gaussian likelihood analysis, we find that each event's non-Gaussian posterior in H_0 helps reduce the overall measurement errors in H_0 for an ensemble of NS binary mergers.