  Supermassive black hole binaries (SMBHBs) are productions of the hierarchical
galaxy formation model. There are many close connections between central SMBH
and its host galaxy because the former plays very important roles on the
formation and evolution of a galaxy. For this reason, the evolution of SMBHBs
in merging galaxies is an essential problem. Since there are many discussions
about SMBHB evolution in gas rich environment, we focus on the quiescent
galaxy, using tidal disruption as a diagnostic tool. Our study is based on a
series of numerical large particle number direct N-body simulations for dry
major mergers. According to the simulation results, the evolution can be
divided into three phases. In phase I, the tidal disruption rate for two well
separated SMBHs in merging system has similar level to single SMBH in isolate
galaxy. After two SMBHs getting close enough to form a bound binary in phase
II, the disruption rate can be enhanced for ~ 2 order of magnitudes within a
short time. This "boosted" disruption stage finishes after the SMBHB evolving
to compact binary system in phase III, corresponding to a drop back of
disruption rate to a level of a few times higher than that in Phase I. How to
correctly extrapolate our N-body simulation results to reality, and
implications of our results to observations, are discussed too.
