Dynamical evolution of massive black holes in galactic-scale N-body
  simulations - introducing the regularized tree code "rVINE"
  We present a hybrid code combining the OpenMP-parallel tree code VINE with an
algorithmic chain regularization scheme. The new code, called "rVINE", aims to
significantly improve the accuracy of close encounters of massive bodies with
supermassive black holes in galaxy-scale numerical simulations. We demonstrate
the capabilities of the code by studying two test problems, the sinking of a
single massive black hole to the centre of a gas-free galaxy due to dynamical
friction and the hardening of a supermassive black hole binary due to close
stellar encounters. We show that results obtained with rVINE compare well with
NBODY7 for problems with particle numbers that can be simulated with NBODY7. In
particular, in both NBODY7 and rVINE we find a clear N-dependence of the binary
hardening rate, a low binary eccentricity and moderate eccentricity evolution,
as well as the conversion of the galaxy's inner density profile from a cusp to
a a core via the ejection of stars at high velocity. The much larger number of
particles that can be handled by rVINE will open up exciting opportunities to
model stellar dynamics close to SMBHs much more accurately in a realistic
galactic context. This will help to remedy the inherent limitations of commonly
used tree solvers to follow the correct dynamical evolution of black holes in
galaxy scale simulations.
