# Standard Siren Cosmology with Gravitational Waves from Binary Black Hole Mergers in Active Galaxy Nuclei

**Authors:** Clecio R. Bom, Antonella Palmese  
**arXiv:** [2307.01330](https://arxiv.org/abs/2307.01330)  
**Date:** 2023-07-03  
**Summary page:** https://www.summarizepaper.com/en/arxiv-id/2307.01330v1/

## Key points

- Detection of gravitational waves (GW) with an electromagnetic counterpart opens up new possibilities for cosmological analyses
- Measurement of the Hubble Constant ($H_0$) through the standard siren method is now feasible
- Binary Black Hole (BBH) mergers detected by LVK often occur in Active Galactic Nuclei (AGN) disks
- Combining GW and AGN data could lead to promising cosmological analyses
- Researchers have developed a method that considers background flaring AGNs without requiring unique host galaxy identification
- Precision in constraining $H_0$ ranges from approximately 3.5% to 7% using about 2 years or 160 events of LVK data at design sensitivity, depending on the fraction of BBHs inducing flares
- With a more restrictive prior on $\Omega_{\rm m}$ and assuming at least 20% of BBHs produce detectable flares, precision in $H_0$ can reach 3% after 2 years of LVK data at design sensitivity
- Even without time-critical follow-up observations, a precision of approximately 5-10% in $H_0$ can be achieved with complete AGN catalogs and just one year of LVK run
- Incorporating information from flaring AGNs improves the precision of $H_0$ measurements and enhances our understanding of cosmology and BBH mergers

## Summary

The detection of gravitational waves (GW) with an electromagnetic counterpart has opened up new possibilities for cosmological analyses. In particular, the measurement of the Hubble Constant ($H_0$) through the standard siren method has become feasible. Recent studies have shown that a significant fraction (approximately 20-80%) of Binary Black Hole (BBH) mergers detected by LIGO/Virgo/KAGRA (LVK) occur in Active Galactic Nuclei (AGN) disks. This association between BBH mergers and flaring AGNs suggests that combining GW and AGN data could lead to promising cosmological analyses. To explore this potential, researchers have developed a method that takes into account the presence of background flaring AGNs without requiring a unique host galaxy identification. They applied this method to realistic GW simulations. Depending on the fraction of LVK BBHs that induce flares, the researchers expect to constrain $H_0$ with a precision ranging from approximately 3.5% to 7% (or 2.5% to 5%) using about 2 years or 160 events (or 1 year or 500 events) of LVK data at design sensitivity, assuming systematic BBH follow-up searches are conducted. By imposing a more restrictive prior on $\Omega_{\rm m}$ and assuming that at least 20% of BBHs produce detectable flares, they anticipate reaching a precision of 3% (or 2%) in $H_0$ after 2 (or 1) year(s) of LVK data at design sensitivity. Furthermore, the researchers demonstrate that even without time-critical follow-up observations, it is possible to achieve a precision of approximately 5-10% in $H_0$ with complete AGN catalogs and just one year of LVK run. Overall, these findings suggest that incorporating information from flaring AGNs in standard siren analyses can significantly improve the precision of $H_0$ measurements. This approach has the potential to enhance our understanding of cosmology and the nature of BBH mergers, paving the way for more accurate and comprehensive cosmological studies using GW and AGN data.