Speaker
Description
We study the dynamics of a binary system orbiting a rotating supermassive black hole (SMBH) and the resulting gravitational-wave signatures from such hierarchical three-body systems. To describe the motion in curved spacetime, we construct a local inertial frame using Fermi–Walker transport and treat the binary as a Newtonian system in this frame.
For a binary whose center of mass follows a circular orbit around a Kerr black hole, we find that von Zeipel–Lidov–Kozai (vZLK) oscillations appear when the initial inclination exceeds a critical angle. This mechanism is characterized by a periodic exchange between the eccentricity of the inner binary and the relative inclination. Because large eccentricity enhances gravitational-wave emission, this mechanism is important in gravitational-wave astronomy. Hard binaries show regular oscillations, while soft binaries exhibit irregular but stable behavior, sometimes accompanied by orbital flips.
We extend the analysis to spherical orbits in Kerr spacetime, where latitudinal libration significantly modifies the oscillations, shortening their period and increasing the maximum eccentricity. The SMBH spin can even reduce the oscillation timescale to the dynamical one. We then analyze typical properties of gravitational waves produced by these effects, especially the vZLK mechanism, which may be detectable by future space-based interferometers. We also discuss eccentric orbits, including binary scattering events.
| Research Area | Gravitational waves: black holes |
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