Origin of the cartwheel galaxy: Disk instability?

The linear theory and N-body simulations are used to present a new, alternative model of the galaxy A0035-324 (the "Cartwheel"), which is the most striking example of the relatively small class of ring galaxies. The model is based on the gravitational Jeans-type instability of both axisymmetric (radial) and nonaxisymmetric (spiral) small-amplitude gravity perturbations (e.g., those produced by spontaneous disturbances) of a dynamically cold subsystem (identified as the gaseous component) of an isolated disk galaxy. The simplified model of a galaxy is used in which stars (and a dark matter, if it exists at all) do not participate in the disk collective oscillations and just form a background charge. In the theory presented here, a case for both purely radial solutions and purely spiral solutions to the equations of motion of an infinitesimally thin gaseous disk is made, which is associated with both a radial density wave and a dominant spiral density wave which propagate outwards creating a rough ring and a number of spiral arms. Through three-dimensional numerical simulation of a collisionless set of many particles, I associate these gravitationally unstable axisymmetric waves and nonaxisymmetric waves with growing clumps of matter which take on the appearance of a ring and spokes of mass blobs.