Numerical modelling of binary black hole dynamics in Active Galactic Nuclei discs

Binary black holes (BBHs) embedded in active galactic nuclei (AGN) discs are potential progenitors of black hole mergers detected via gravitational waves (GW) by LIGO consortium. Mergers within AGN discs where binary is embedded in a high-density environment, are the only GW channel where an electromagnetic (EM) counterpart must occur (whether it is detectable or not). We present a series of high-resolution simulations investigating the orbital dynamics of BBHs within AGN discs , focusing on how mass ratio, orbital orientation, and magnetic field configuration impact their dynamics and any affect on emissions due to these. Special attention is given to mass accretion rates and angular momentum exchange, as these processes play a crucial role in determining the long-term evolution and eventual merger timescales of BBHs. Two main simulation sets were conducted: one for prograde binaries, where the BBH orbit aligns with the disc’s rotation, which reveals inward orbital migration driven by angular momentum transfer; and the other for retrograde binaries, which are oppositely aligned, demonstrating higher angular momentum loss rates. Under the progarde set we also cover non-unity mass ratios and check its dependence on torque and variability. Our findings show that there is preferential accretion on the small component of the binary. We also perform a suite of viscous hydrodynamical simulations of equal-mass binaries. We find that viscosity significantly increases the accretion rates of prograde circular binaries. Furthermore, the role of different magnetic field configurations in modulating torque and BBH evolution is also examined.