LIGO Document P1800338-v6
- We present a multi--messenger measurement of the Hubble constant \( H_0 \) using the binary--black--hole merger GW170814 as a standard siren, combined with a photometric redshift catalog from the Dark Energy Survey (DES). The luminosity distance is obtained from the gravitational wave signal detected by the LIGO/Virgo Collaboration (LVC) on 2017 August 14, and the redshift information is provided by the DES Year 3 data. Black--hole mergers such as GW170814 are expected to lack bright electromagnetic emission to uniquely identify their host galaxies and build an object--by--object Hubble diagram. However, they are suitable for a statistical measurement, provided that a galaxy catalog of adequate depth and redshift completion is available. In this work, we establish the first Hubble parameter measurement using a black--hole merger. Our analysis results in \( H_0 = 75.2^{+39.5}_{-32.4}~{\rm km~s^{-1}~Mpc^{-1}} \), which is consistent with both SN Ia and CMB measurements of the Hubble constant. The quoted 68\% credible region comprises 60\% of the uniform prior range [20,140] \( {\rm km~s^{-1}~Mpc^{-1}} \). This result shows that even a single dark siren can provide a constraint on the Hubble constant, albeit a weak one. Future combinations of many sirens will lead to improved constraints. A multifold increase in the LVC event detection rate is expected in the coming years, and this bodes well since future combinations of many additional sirens will lead to improved constraints.
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