Violent Relaxation...
...sounds like a new form of extreme sports for the overly energetic, but it's actually a process of some importance in galaxy formation. The virial theorem relates the time average of the kinetic energy of a system of gravitationally bound particles to its potential energy: Tav = -(1/2)V. A system in which this kinetic energy is close to this average is called relaxed. Suppose one starts with an arrangement of, say 100, mass particles with random velocities and turns on gravity. Initially, there is no particular relation between the total kinetic energy and the potential energy (except they should be bound, so T +V One process that leads to relaxation is gravitational encounters between pairs of individual particles , which tends to equipartition kinetic energies. The time to relaxation in such encounters depends on the density and number of particles. For an open cluster of about 100 stars, relaxation times are roughly ten million years, while for for globular cluster of 1...