 Stellar dynamics

Stellar dynamics treats stars as gravitating bodies whose collective motions reveal and reshape their environment. In a collisionless stellar system, stars mainly follow the smooth collective gravitational potential; in a sufficiently dense star cluster, accumulated gravitational encounters produce two-body relaxation. These encounters need not involve physical contact between stars. Observers combine astrometry with radial velocities to constrain orbits and infer unseen mass. The stellar orbits at the Galactic centre provide a particularly direct example: following a short-period star around Sagittarius A* measures the compact central mass, rather than estimating it from the light emitted by its surroundings.^[ref]

Stellar dynamics is a branch of astrophysics that deals with the study of the motions, interactions, and behaviors of stars within galaxies and star clusters. This field combines principles of mechanics, gravity, and statistical methods to understand how stars move and influence one another under the gravitational forces present in these systems.