Massive black hole binary plane reorientation in rotating stellar
  systems
  We study the evolution of the orientation of the orbital plane of massive
black hole binaries (BHBs) in rotating stellar systems in which the total
angular momentum of the stellar cusp is misaligned with respect to that of the
binary. We compare results from direct summation N-body simulations with
predictions from a simple theoretical model. We find that the same encounters
between cusp stars and the BHB that are responsible for the hardening and
eccentricity evolution of the binary, lead to a reorientation of the binary
orbital plane. In particular, binaries whose angular momentum is initially
misaligned with respect to that of the stellar cusp tend to realign their
orbital planes with the angular momentum of the cusp on a timescale of a few
hardening times. This is due to angular momentum exchange between stars and the
BHB during close encounters, and may have important implications for the
relative orientation of host galaxies and radio jets.
