Galactic Dynamics
First published: 2008
Brief summary
Scholarpedia overview of orbital motion, resonances and waves in galaxies.
Article
Galactic dynamics examines the motion of stars, gas and dark matter under their collective gravitational field. Because a galaxy contains very many bodies, its evolution is usually described with statistical distribution functions and a smooth gravitational potential rather than by following every individual encounter.
Stars follow orbits determined by the galaxy’s mass distribution. In nearly symmetric systems, conserved quantities such as energy and angular momentum help classify those orbits, while departures from symmetry produce more complicated regular or chaotic trajectories.
Spiral arms, bars and other patterns can be treated as organised disturbances in the stellar and gaseous disc. Resonances occur where combinations of orbital frequencies match the rotation rate of a pattern, allowing exchanges of energy and angular momentum.
These processes influence the shape, stability and secular evolution of galaxies. Dynamical models are used to infer unseen mass, interpret rotation curves and stellar velocities, and study how bars, spiral structure, interactions and mergers redistribute matter over time.
Source details and credits
- Source / publisher: Scholarpedia
- Source type: Reference article
- URL type: WWW
- Credits: Scholarpedia
- URL: http://www.scholarpedia.org/article/Galactic_dynamics