A Hubble constant measurement from superluminal motion of the jet in GW170817
Abstract
The Hubble constant (H_{0}) measures the current expansion rate of the Universe, and plays a fundamental role in cosmology. Tremendous effort has been dedicated over the past decades to measure H_{0} (refs. ^{110}). Gravitational wave (GW) sources accompanied by electromagnetic (EM) counterparts offer an independent standard siren measurement of H_{0} (refs. ^{1113}), as demonstrated following the discovery of the neutron star merger, GW170817 (refs. ^{1416}). This measurement does not assume a cosmological model and is independent of a cosmic distance ladder. The first joint analysis of the GW signal from GW170817 and its EM localization led to a measurement of H_{0}=7 4_{8}^{+16}km s^{1}Mpc^{1} (median and symmetric 68% credible interval)^{13}. In this analysis, the degeneracy in the GW signal between the source distance and the observing angle dominated the H_{0} measurement uncertainty. Recently, tight constraints on the observing angle using high angular resolution imaging of the radio counterpart of GW170817 have been obtained^{17}. Here, we report an improved measurement H_{0}=70 .3_{5.0}^{+5.3}km s^{1}Mpc^{1} by using these new radio observations, combined with the previous GW and EM data. We estimate that 15 more GW170817like events, having radio images and light curve data, as compared with 50100 GW events without such data^{18,19}, will potentially resolve the tension between the Planck and Cepheidsupernova measurements.
 Publication:

Nature Astronomy
 Pub Date:
 July 2019
 DOI:
 10.1038/s4155001908201
 arXiv:
 arXiv:1806.10596
 Bibcode:
 2019NatAs...3..940H
 Keywords:

 Astrophysics  Cosmology and Nongalactic Astrophysics;
 Astrophysics  High Energy Astrophysical Phenomena;
 General Relativity and Quantum Cosmology
 EPrint:
 29 pages, 9 figures