Dr. Sumedha Biswas

Binary black hole (BBH) mergers are expected to be dark sirens, producing no detectable electromagnetic counterparts and therefore making it difficult to identify their host galaxies. However, a unique host association would be highly informative: it would allow us to directly probe the environments of BBH progenitors, distinguish BBH formation channels, and enable independent measurements of the Hubble constant. I investigate this using simulations of BBH mergers in nearby galaxies with future GW detector networks, including LIGO-India, Cosmic Explorer, and the Einstein Telescope. We compute 3D localization volumes using the Fisher Information Matrix approximation, and compare them to a suite of theoretical diagnostics, including galaxy stellar mass function thresholds weighted by BBH formation channels, metallicity constraints, and the probability of 3D chance alignment. We find that next-generation detector networks routinely localize BBH mergers to volumes smaller than these theoretical limits, implying that unique host-galaxy associations may be achievable out to ~1000 Mpc at a rate of ~100 events per year. This establishes a framework to directly connect BBH mergers to their progenitor environments and formation channels. I conclude by discussing extensions of this framework, including a broader parameter space, modeling galaxy catalogue incompleteness, and considering additional BBH formation channels, and what these developments imply for host identification in the 3G era. I also discuss how spectroscopic redshifts from the WEAVE survey can deliver precise H0 measurements from BBH dark sirens, providing an independent probe of the Hubble tension in the coming decade.