  In this note we discuss the main results of a study of a massive binary with
unequal mass ratio, q, embedded in an accretion disk, with its orbital rotation
being opposed to that of the disk. When the mass ratio is sufficiently large, a
gap opens in the disk, but the mechanism of gap formation is very different
from the prograde case. Inward migration occurs on a timescale of t_ev ~
M_p/(dot M), where M_p is the mass of the less massive component (the
perturber), and dot M is the accretion rate. When q<< 1, the accretion takes
place mostly onto the more massive component, with the accretion rate onto the
perturber being smaller than, or of order of, q^(1/3)M. However, this rate
increases when supermassive binary black holes are considered and gravitational
wave emission is important. We estimate a typical duration of time for which
the accretion onto the perturber and gravitational waves could be detected.
