STATISTICAL-MECHANICS OF GALAXIES

An analysis, aimed at clarifying the predictions of statistical mechanics for collisionless stellar systems, is presented. This is motivated by the recent success of maximum entropy-like principles applied to the structure of elliptical galaxies. It is argued that the strong divergence of trajectories in gravitational N-body systems leads to a very small mixing scale and to a non-degenerate distribution function. In addition, the physics of violent relaxation favours a well-mixed equilibrium independently of initial conditions. Under these circumstances, the statistical mechanical prediction can explain the universal structure of elliptical galaxies.