Spherical N-Body Collapse

Left: Four snapshots from an N-body collapse similar to the movie shown before. (a) As before, an initially uniform density sparse sphere with small random velocities collapses. (b) Inhomogeneities grow so the initial collapse has a rather chaotic minimum size. (c) Rebound ejects some stars while the rest remain centrally concentrated. (d) The final distribution resembles a deVaucauleurs law. Right: The initial and final density distributions. Constant density becomes roughly de Vaucouleurs law.
Left: Distribution of star energies. Initially (dashed) a narrow spike of weakly bound stars (low velocities in a large region). At first collapse (grey) the spread in energy is largest, with some very bound stars. The final distribution (solid) has some unbound stars (E > 0). Right: Anisotropy parameter shows isotropic velocities at the center, becoming increasingly radially anisotropic with increasing radius. The orbits of the outermost stars are purely radial.
Original paper: van Albada 1982 [o-link].