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Astro Seminar

Gravitational-wave standard siren probes of cosmology

Speaker: Jonathan Gair (MPG)
Date: Wednesday 24 February 2021
Time: 14:00
Venue: Zoom

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, was consistent with current electromagnetic measurements, albeit not competitive with their precision. This result has since been enhanced by folding in statistical information from dark standard sirens, i.e., gravitational wave events without counterparts, and is expected to rapidly improve with the order of magnitude increase in events expected for near future detectors. Such standard siren measurements of cosmological parameters will suffer from a completely different set of systematic uncertainties to existing electromagnetic measurements and thus could offer a potential resolution of existing tensions in current cosmological measurements. In this talk I will describe the first gravitational wave Hubble constant measurements, discuss prospects for improving this result over the next two decades and describe some of the potential sources of systematic error that could limit the accuracy of the final result.