Gaseous Disks of Spiral Galaxies: Arms and Rings
  An improved linear stability theory of small-amplitude oscillations of a self-gravitating, infinitesimally thin gaseous disk of spiral galaxies has been developed. It was shown that in the differentially rotating disks for nonaxisymmetric perturbations Toomre's modified hydrodynamical simulations to test the validity of the modified local criterion. 
Edward Liverts (1,2), Evgeny Griv (2), Michael Gedalin (2) David   Eichler (2), and Chi Yuan (3) ((1) Department of Theoreti...