The Eccentric Kozai-Lidov Effect and Its Applications

Abstract

The hierarchical triple-body approximation has useful applications to a variety of systems from planetary and stellar scales to supermassive black holes. In this approximation, the energy of each orbit is separately conserved, and therefore the two semimajor axes are constants. On timescales much larger than the orbital periods, the orbits exchange angular momentum, which leads to eccentricity and orientation (i.e., inclination) oscillations. The orbits' eccentricity can reach extreme values, leading to a nearly radial motion, which can further evolve into short orbit periods and merging binaries. Furthermore, the orbits' mutual inclinations may change dramatically from pure prograde to pure retrograde, leading to misalignment and a wide range of inclinations. This dynamical behavior is coined the “eccentric Kozai-Lidov mechanism.” The behavior of such a system is exciting, rich, and chaotic in nature. Furthermore, these dynamics are accessible from a large part of the triple-body parameter space and can be applied to a diverse range of astrophysical settings and used to gain insights into many puzzles.