CCA Colloquium: Saavik Ford

Title: AGN disks have things in them–and those things are important

Abstract: Active Galactic Nuclei (AGN) have usually been modeled and conceptualized solely in terms of their gas content. However, given the existence of Nuclear Star Clusters (NSCs) it is reasonable to expect stars and stellar remnants will also exist in AGN disks. Their presence leads to several important consequences, notably the AGN-driven channel for mergers of compact objects, detectable with ground-based GW observatories like LIGO-Virgo. I will discuss the mechanisms and open questions of the AGN channel, including the successful predictions of the channel to date. In addition, because mergers of binary black holes in AGN disks occur in the presence of gas, there is the possibility of naturally generating detectable EM counterparts to these mergers. I will discuss the public candidate counterpart and future directions for further searches. Finally, the existence of GW-EM sources provides an independent way of measuring the Hubble Constant, H_0. With sufficient numbers of confirmed AGN GW-EM counterparts, BBH may provide the tightest constraints on the measurement of H_0, and can resolve the tension between SNe- and CMB-based measurements.

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