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Astrophysics, High Energy Astrophysical Phenomena, astro-ph.HE,General Relativity and Quantum Cosmology, gr-qc
Abstract:
Kozai-Lidov (KL) oscillations can accelerate compact object mergers via
gravitational wave (GW) radiation by driving the inner binaries of hierarchical
triples to high eccentricities. We perform direct three-body integrations of
high mass ratio compact object triple systems using Fewbody including
post-Newtonian terms. We find that the inner binary undergoes rapid
eccentricity oscillations (REOs) on the timescale of the outer orbital period
which drive it to higher eccentricities than secular theory would otherwise
predict, resulting in substantially reduced merger times. For a uniform
distribution of tertiary eccentricity ($e_2$), ~40% of systems merge within
~1-2 eccentric KL timescales whereas secular theory predicts that only ~20% of
such systems merge that rapidly. This discrepancy becomes especially pronounced
at low $e_2$, with secular theory overpredicting the merger time by many orders
of magnitude. We show that a non-negligible fraction of systems have
eccentricity > 0.8 when they merge, in contrast to predictions from secular
theory. Our results are applicable to high mass ratio triple systems containing
black holes or neutron stars. In objects in which tidal effects are important,
such as white dwarfs, stars, and planets, REOs can reduce the tidal
circularization timescale by an order of magnitude and bring the components of
the inner binary into closer orbits than would be possible in the secular
approximation.
