  We use a hybrid N-body program to study the evolution of massive black hole
binaries in the centers of galaxies, mainly to understand the factors affecting
the binary eccentricity, the response of the galaxy to the binary merger, and
the effect of loss-cone depletion on the merger time. The scattering
experiments from paper I showed that the merger time is not sensitive to the
eccentricity growth unless a binary forms with at least a moderate
eccentricity. We find here that the eccentricity can become large under some
conditions if a binary forms in a galaxy with a flat core or with a radial bias
in its velocity distribution, especially if the dynamical friction is enhanced
by resonances as suggested by Rauch and Tremaine (1996). But the necessary
conditions all seem unlikely, and our prediction from paper I remains
unchanged: in most cases the eccentricity will start and remain small. As a
binary hardens it ejects stars from the center of a galaxy, which may explain
why large elliptical galaxies have weaker density cusps than smaller galaxies.
If so, the central velocity distributions in those galaxies should have strong
tangential anisotropies. The wandering of a binary from the center of a galaxy
mitigates the problems associated with loss-cone depletion and helps the binary
merge.
