Stellar dynamics

Stellar dynamics studies how gravity governs the motions and interactions of stars in systems such as galaxies, star clusters, and multiple-star systems.

N-body problem: The problem of predicting the motions of multiple bodies interacting through forces such as gravity. Stellar systems are gravitational many-body systems whose trajectories the N-body problem seeks to describe.
Phase space: A space whose coordinates represent the positions and momenta of a physical system. A star’s phase-space coordinates encode both its location and motion.
Galactic dynamics: The study of the motions and gravitational evolution of stars and other matter within galaxies. It applies stellar-dynamical methods to the structure and evolution of entire galaxies.
Stellar evolution: The physical changes a star undergoes over its lifetime, driven chiefly by its internal structure and nuclear reactions. It follows changes inside individual stars, unlike dynamics, which follows motion and gravitational interactions.
Virial theorem: A relation connecting time-averaged kinetic and potential energies in a bound system. It links stellar speeds to a system’s gravitational binding and helps estimate masses.
Distribution function (astrophysics): A function giving the density of stars in position and velocity space. It represents an entire stellar population rather than tracking each star separately.
Star cluster: A group of stars bound together by their mutual gravity. Clusters expose the effects of repeated stellar encounters and long-term gravitational evolution.
Celestial mechanics: The study of the motions of celestial bodies under gravity, especially in planetary and satellite systems. It is the broader gravitational-motion field from which stellar dynamics takes its methods and problems.
Two-body problem: The problem of determining the motion of two bodies interacting through a central force. It supplies the orbital baseline before additional stars perturb a system.
Gravitational potential: A scalar field whose spatial gradient determines the gravitational acceleration. It summarizes the gravitational field that drives stellar orbits.

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