Determining the Hubble Constant with AGN-assisted Black Hole Mergers

TL;DR

This paper proposes using black hole mergers within Active Galactic Nuclei disks as a new method to measure the Hubble constant with gravitational waves, potentially improving current measurement precision.

Contribution

It introduces the idea that AGN-assisted black hole mergers can serve as a sensitive new probe for determining the Hubble constant.

Findings

Black hole mergers in AGN disks can measure H_0 with 4-12% uncertainty in five years.

Identified host galaxies of 1-5% of mergers could significantly improve H_0 measurements.

This method could match or surpass the sensitivity of neutron star merger-based measurements.

Abstract

Gravitational waves from neutron star mergers have long been considered a promising way to measure the Hubble constant, $H_0$, which describes the local expansion rate of the universe. While black hole mergers are more abundantly observed, their expected lack of electromagnetic emission and poor gravitational-wave localization make them less well suited for measuring $H_0$. Black hole mergers within the disks of Active Galactic Nuclei (AGN) could be an exception. Accretion from the AGN disk may produce an electromagnetic signal, pointing observers to the host galaxy. Alternatively, the low number density of AGNs could help identify the host galaxy of $1-5\%$ of mergers. Here we show that black hole mergers in AGN disks may be a sensitive way to determine $H_0$ with gravitational waves. If $1\%$ ($10\%$) of LIGO's observations occur in AGN disks with identified host galaxies, we could measure $H_0$ with $12\%$ ($4\%$) uncertainty in five years, possibly comparable to the sensitivity of neutron star mergers and set to considerably improve current gravitational wave measurements.