The measurement of the Hubble–Lemaître constant (H0) from the cosmic microwave background and the Type IA supernovae are at odds with each other. One way to resolve this tension is to use an independent way to measure H0. This can be accomplished by using gravitational-wave (GW) observations. Previous works have shown that with the onset of the next generation of GW detector networks, it will be possible to constrain H0 to better than 2 per cent precision (which is enough to resolve the tension) with binary black hole systems that are extremely well localized in the sky, also called golden dark sirens. Bright sirens like binary neutron star systems can also help resolve the tension if both the GW and the following electromagnetic counterpart are detected. In this work, we show that neutron star-black hole (NSBH) mergers can act both as golden dark sirens as well as bright sirens, thus, assigning them the term grey sirens. We assess the potential of using NSBH mergers to measure H0 and find that the Voyager network might be able to resolve the tension in an observation span of 5 yr. The next generation networks, which include the Cosmic Explorer detectors and the Einstein Telescope will be able to measure H0 to sub-per cent level just by using NSBH mergers.
Gravitational waves from neutron star mergers have long been considered a promising way to measure the Hubble constant, H0, 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 H0. Black hole mergers within the discs of Active Galactic Nuclei (AGN) could be an exception. Accretion from the AGN disc 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 $1{\!-\!}5~{{\ \rm per\ cent}}$ of mergers. Here we show that black hole mergers in AGN discs may be a sensitive way to determine H0 with gravitational waves. If 1 per cent (10 per cent) of LIGO’s observations occur in AGN discs with identified host galaxies, we could measure H0 with 12 per cent (4 per cent) uncertainty in five years, possibly comparable to the sensitivity of neutron star mergers and set to considerably improve current gravitational wave measurements.
more » « less- PAR ID:
- 10514181
- Publisher / Repository:
- Oxford University Press
- Date Published:
- Journal Name:
- Monthly Notices of the Royal Astronomical Society
- Volume:
- 531
- Issue:
- 3
- ISSN:
- 0035-8711
- Format(s):
- Medium: X Size: p. 3679-3683
- Size(s):
- p. 3679-3683
- Sponsoring Org:
- National Science Foundation
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