BINARY-DISK INTERACTION: GAP-OPENING CRITERIA

We study the interaction of an equal mass binary with an isothermal circumbinary disk motivated by the evidence of the formation of massive black hole binaries surrounded by gas, after a major merger of gas-rich galaxies. We focus on the torques that the binary produces on the disk and how the exchange of angular momentum can drive the gap formation on it. We propose that the angular momentum exchange between the binary and the disk is through the gravitational interaction of the binary and a (tidally formed) global non-axisymmetric perturbation in the disk. Using this interaction, we derive an analytic criterion for the gap formation in the disk that can be expressed either via the characteristic velocities of the binary-disk system or in terms of the structural parameters h/a and M(