School of Physics CRA Seminar: Speaker Li Gongjie, Harvard-Smithsonian Center for Astrophysics

This talk presents a series of studies on the dynamics of high mass ratio multiples. I will first focus on the hierarchical three-body dynamics. The secular dynamical evolution of a hierarchical three body system, in which a distant third object orbits around a binary has been studied extensively, demonstrating that the inner orbit can undergo large eccentricity and inclination oscillations. It had been shown before that starting with a circular inner orbit, large mutual inclination (40 - 140 degree) can produce long timescale modulations that drive the eccentricity to extremely large values and can flip the orbit.

 I will demonstrate that starting with an almost coplanar configuration, for non-circular inner and outer orbits, the eccentricity of the inner orbit can still be excited to high values, and the orbit can flip by ~180 degree, rolling over its major axis. The ~180 degree flip is caused by octopole resonances, and the flip criterion and timescale are described by simple analytic expressions that depend on initial orbital parameters. This mechanism can produce counter-orbiting exo-planetary systems under tidal dissipation. It can also change the stellar distribution around binary black hole systems.

In addition, I will briefly summarize some of the non-hierarchical dynamical features
that can be found in planetary systems and stellar systems around supermassive black holes. These include the spin-orbit misalignment due to orbital precession (with application to exo-planetary system Kepler 56), the scattering encounters in clusters which sculpt the planetary system configuration, the obliquity (spin-orbit) variation of planets, and heating of stars around supermassive black holes by gravitational waves and by tides.