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Abstract
The hierarchical galaxy formation picture suggests that super massive black holes
(MBHs) observed in galactic nuclei today have grown from coalescence of massive black
hole binaries (MBHB) after galaxy merging. Once the components of a MBHB become gravitationally
bound, strong three-body encounters between the MBHB and stars dominate its evolution
in a "dry" gas free environment, and change the MBHB's energy and angular momentum
(semi-major axis, eccentricity and orientation). Here we present high accuracy direct
N-body simulations of spherical and axisymmetric (rotating) galactic nuclei with order
a million stars and two massive black holes that are initially unbound. We analyze
the properties of the ejected stars due to slingshot effects from three-body encounters
with the MBHB in detail. Previous studies have investigated the eccentricity and energy
changes of MBHs using approximate models or Monte-Carlo three body scatterings. We
find general agreement with the average results of previous semi-analytic models for
spherical galactic nuclei, but our results show a large statistical variation. Our
new results show many more phase space details of how the process works, and also
show the influence of stellar system rotation on the process. We detect that the angle
between the orbital plane of the MBHBs and that of the stellar system (when it rotates)
influences the phase-space properties of the ejected stars. We also find that massive
MBHB tend to switch stars with counter-rotating orbits into co-rotating orbits during
their interactions.