Orbital evolution of binary black holes in active galactic nucleus disks: a disk channel for binary black hole mergers?

Understand

We perform a series of high-resolution 2D hydrodynamical simulations of equal-mass binary black holes (BBHs) embedded in active galactic nucleus (AGN) accretion disks to study whether these binaries can be driven to merger by the surrounding gas.

• We find that the gravitational softening adopted for the BBH has a profound impact on this result.
• When the softening is less than ten percent of the binary separation, we show that, in agreement with recent simulations of isolated equal-mass binaries, prograde BBHs expand in time rather than contract.
• Eventually, however, the binary separation becomes large enough that the tidal force of the central AGN disrupts them.