  We examine whether massive binary black holes in spherically symmetric bulges
of galaxies can achieve coalescence through the emission of gravitational
radiation under the action of stellar dynamical processes alone. In particular,
we address the importance of the Brownian motion of a binary's center-of-mass
to its continued interaction with stellar orbits that allows it to keep
hardening: the restoring force holding the binary at the center decreases as it
depletes the central stellar density, causing the amplitude of wandering to
increase. We use an analytical model and N-body simulations to calculate the
time required to reach the gravitational-radiation dominated stage. We find
that a substantial fraction of all massive binaries in galaxies can coalesce
within a Hubble time.
