Numerical Experiments with a Disk of Stars

The evolution of an initially balanced rotating disk of stars with an initial velocity dispersion given by Toomre's local criterion is investigated by means of a computer model for isolated disks of stars. It is found that the disk is unstable against very large-scale modes. After about two rotations the central portion of the disk tends to assume a bar-shaped structure. A stable axisymmetric disk with a velocity dispersion much larger than that given by Toomre's criterion is generated. The final mass distribution for the disk gives a high-density central core and a disk population of stars that is closely approximated by an exponential variation.