Abstract

On 17th August 2017, the Advanced LIGO and Virgo interferometers observed gravitational waves from the inspiral and merger of a binary neutron star system for the first time. An optical counterpart to the event was observed the following night, which allowed the unique identification of the host galaxy of the event and hence a determination of its redshift. The combination of a measurement of luminosity distance from the gravitational wave signal with the electromagnetic redshift measurement allowed the local expansion rate of the Universe, the Hubble constant, to be estimated. The final result, H0 = 70 +12/-8 km/s/Mpc, is consistent with current electromagnetic measurements, albeit not competitive with their precision. However, such standard siren measurements of cosmological parameters are largely independent of existing techniques and hence will provide a powerful verification of these other results. In this talk I will provide details of the first gravitational wave Hubble constant measurement and then discuss prospects for improving this result over the next two decades, using further binary neutron star mergers with counterparts, using statistical cross-correlation of gravitational wave events with galaxy catalogues in the absence of counterparts and using sources observed with other planned gravitational wave detectors.