CRA Seminar: Rixin Li (Cornell)

Title: Hydrodynamical Evolution of Binary Black Holes Embedded in AGN Disks

Abstract: Stellar-mass binary black holes (BBHs) embedded in active galactic nucleus (AGN) disks are promising progenitors of black hole mergers detected in gravitational waves (GW) by LIGO-VIRGO-KAGRA. Current observed mergers show distinct properties that may only be explained by this AGN channel, with a few potentially associated electromagnetic counterparts identified. However, the hydrodynamical evolution of stellar-mass BBHs interacting with disk gas was poorly understood and lacked numerical studies. In this talk, I will present our high-resolution simulations of binaries in local disk models, with an extensive coverage of parameter space. We find that circular comparable-mass binaries contract, with an orbital decay rate of a few times the mass doubling rate. I will demonstrate that less massive and wider binaries embedded in disks with a non-isothermal equation of state and a low viscosity are easier to be hardened. In addition, our results suggest that the hardening time-scales of BBHs are much shorter than their migration time-scales in AGN disks. Finally, I will briefly describe recent progresses made in this topic and future prospects.