Gas pile-up, gap overflow, and Type 1.5 migration in circumbinary disks: application to supermassive black hole binaries

Understand

We study the interaction of a supermassive black hole (SMBH) binary and a standard radiatively efficient thin accretion disk.

• We examine steady-state configurations of the disk and migrating SMBH system, self-consistently accounting for tidal and viscous torques and heating, radiative diffusion limited cooling, gas and radiation pressure, and the decay of the binary's orbit.
• We obtain a "phase diagram" of the system as a function of binary parameters, showing regimes in which both the disk structure and migration have a different character.
• Although massive binaries can create a central gap in the disk at large radii, the tidal barrier of the secondary causes a significant pile-up of gas outside of its orbit, which can lead to the closing of the gap.