Stellar dynamics

Summary

Stellar dynamics studies the motion of stars, or other point masses, under their mutual gravity in systems such as star clusters, galaxies and galaxy clusters. These systems contain from thousands to hundreds of billions of stars, so they are described statistically. The description uses a distribution function in phase space. It obeys the Vlasov equation, also called the collisionless Boltzmann equation, coupled with Poisson's equation. Close encounters between individual stars are rare and act slowly, so on short time scales a stellar system behaves as a collisionless fluid. The field connects celestial mechanics with kinetic theory and supplies the models used to measure masses of galaxies and dark matter halos.