Black Hole and Neutron Star Binary Mergers in Triple Systems: II. Merger Eccentricity and Spin-Orbit Misalignment. (arXiv:1905.00427v1 [astro-ph.HE])
<a href="http://arxiv.org/find/astro-ph/1/au:+Liu_B/0/1/0/all/0/1">Bin Liu</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Lai_D/0/1/0/all/0/1">Dong Lai</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Wang_Y/0/1/0/all/0/1">Yi-Han Wang</a>
We study the dynamical signatures of black hole (BH) and neutron star (NS)
binary mergers via Lidov-Kozai oscillations induced by tertiary companions in
hierarchical triple systems. For each type of binaries (BH-BH and BH-NS), we
explore a wide range of binary/triple parameters that lead to binary mergers,
and determine the distributions of eccentricity ($e_mathrm{m}$) and spin-orbit
misalignment angle ($theta_rm {sl}^rm f$) when the binary enters the
LIGO/VIRGO band. We use the double-averaged (over both orbits) and
single-averaged (over the inner orbit) secular equations, as well as N-body
integration, to evolve systems with different hierarchy levels, including the
leading-order post-Newtonian effect, spin-orbit coupling and gravitational
radiation. We find that for merging BH-BH binaries with comparable masses,
about $7%$ have $e_mathrm{m}>0.1$ and $0.7%$ have $e_{rm m}>0.9$. The
majority of the mergers have significant eccentricities in the LISA band. The
BH spin evolution and $theta_rm {sl}^rm f$ are correlated with the orbital
evolution and $e_{rm m}$. Mergers with $e_{rm m} lesssim 10^{-3}$ have a
distribution of $theta_rm {sl}^rm f$ that peaks around $90^circ$ (and thus
favoring a projected binary spin parameter $chi_{rm eff}sim 0$), while
mergers with larger $e_{rm m}$ have a more isotropic spin-orbit misalignments.
For typical BH-NS binaries, strong octuple effects lead to more mergers with
non-negligible $e_mathrm{m}$ (with $sim 18%$ having $e_mathrm{m}>0.1$ and
$2.5%$ having $e_mathrm{m}>0.9$), and the final BH spin axis tends to be
randomly orientated. Measurements or constraints on eccentric mergers and
$theta_rm {sl}^rm f$ from LIGO/VIRGO and LISA would provide useful
diagnostics on the dynamical formation of merging BH or NS binaries in triples.
We study the dynamical signatures of black hole (BH) and neutron star (NS)
binary mergers via Lidov-Kozai oscillations induced by tertiary companions in
hierarchical triple systems. For each type of binaries (BH-BH and BH-NS), we
explore a wide range of binary/triple parameters that lead to binary mergers,
and determine the distributions of eccentricity ($e_mathrm{m}$) and spin-orbit
misalignment angle ($theta_rm {sl}^rm f$) when the binary enters the
LIGO/VIRGO band. We use the double-averaged (over both orbits) and
single-averaged (over the inner orbit) secular equations, as well as N-body
integration, to evolve systems with different hierarchy levels, including the
leading-order post-Newtonian effect, spin-orbit coupling and gravitational
radiation. We find that for merging BH-BH binaries with comparable masses,
about $7%$ have $e_mathrm{m}>0.1$ and $0.7%$ have $e_{rm m}>0.9$. The
majority of the mergers have significant eccentricities in the LISA band. The
BH spin evolution and $theta_rm {sl}^rm f$ are correlated with the orbital
evolution and $e_{rm m}$. Mergers with $e_{rm m} lesssim 10^{-3}$ have a
distribution of $theta_rm {sl}^rm f$ that peaks around $90^circ$ (and thus
favoring a projected binary spin parameter $chi_{rm eff}sim 0$), while
mergers with larger $e_{rm m}$ have a more isotropic spin-orbit misalignments.
For typical BH-NS binaries, strong octuple effects lead to more mergers with
non-negligible $e_mathrm{m}$ (with $sim 18%$ having $e_mathrm{m}>0.1$ and
$2.5%$ having $e_mathrm{m}>0.9$), and the final BH spin axis tends to be
randomly orientated. Measurements or constraints on eccentric mergers and
$theta_rm {sl}^rm f$ from LIGO/VIRGO and LISA would provide useful
diagnostics on the dynamical formation of merging BH or NS binaries in triples.
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