Kozai mechanism

In celestial mechanics, the Kozai mechanism is a dynamical phenomenon affecting the orbit of a binary system perturbed by a distant third body under certain conditions. The mechanism is also named von Zeipel-Kozai-Lidov, Lidov–Kozai, Kozai–Lidov, or some combination of Kozai, Lidov, and/or von Zeipel. It also termed an effect, oscillations, cycles, or resonance. This effect causes the orbit's argument of pericenter to oscillate about a constant value, which in turn leads to a periodic exchange between its eccentricity and inclination. The process occurs on timescales much longer than the orbital periods. It can drive an initially near-circular orbit to arbitrarily high eccentricity, and flip an initially moderately inclined orbit between a prograde and a retrograde motion.

The effect has been found to be an important factor shaping the orbits of irregular satellites of the planets, trans-Neptunian objects, extrasolar planets, and multiple star systems.^[1]: v It hypothetically promotes black hole mergers.^[2] It was described in 1961 by Mikhail Lidov while analyzing the orbits of artificial and natural satellites of planets.^[3] In 1962, Yoshihide Kozai published this same result in application to the orbits of asteroids perturbed by Jupiter.^[4] The citations of the papers by Kozai and Lidov have risen sharply in the 21st century. As of 2017^[update], the mechanism is among the most studied astrophysical phenomena.^[1]: vi It was pointed out in 2019 by Takashi Ito and Katsuhito Ohtsuka that the Swedish astronomer Edvard Hugo von Zeipel had also studied this mechanism in 1909, and his name is sometimes now added.^[5]