Collisionless system.

Click to see animation (24 Mb .mov file).

The movie gives a good feel for the internal motions within a self-gravitating collisionless system, such as a globular cluster or elliptical galaxy. Each star follows a smooth orbit defined by the gravitational field of all the others. There are no collisions -- either direct, or large angle deflections. The movie adopts a slowly rotating viewing frame, which confuses your ability to judge the rotation (if any) of the star cluster. The N-body calculation and movie were made by John Dubinsky (U Toronto).