THE STRUCTURE, EVOLUTION AND INSTABILITY OF A SELF-GRAVITATING GASEOUS DISK UNDER THE INFLUENCE OF PERIODIC FORCINGS

Spiral structure is the most distinguished feature common in all astrophysical disks. One of the ways the spirals can be generated is through an external periodic force in a mechanism known as the resonance excitation. We will use numerical simulations to demonstrate this process for galactic disks. A rotating bar potential or a potential due to spiral waves, both of stellar origin, acts as a periodic forcing to be imposed on a gaseous disk in a disk galaxy. We will show how the spiral density waves are generated, the mass of the disk is re-distributed, and the instability results. In other words, we show in simulations the structure, evolution and instability of the disk subject to such a periodic forcing. The instability which leads to turbulence and chaos of the disk can be identified to be of the types of Rayleigh’s shear instability and Toomre’s gravitational instability, or a combination of both. The results are generally shown in movies and some analyses are given. The work is in parts supported by a grant from National Science Council, Taiwan, NSC94-2752-M-001-002-PAE.