STABILITY OF SELF-GRAVITATING ASTROPHYSICAL DISKS

Criteria which guarantee the stability of self-gravitating gaseous and stellar disks toward any localized small perturbations are obtained. These criteria are formulated as inequalities of the form Q > Q(c) (se parately for gas and stars). The latter should be satisfied by the ''s tability parameter'' Q, which is equal, by definition, to unity on the stability boundary of radial perturbations. The critical value of the stability parameter Q(c) is appreciably greater than (although of the order of) unity, attesting to the great instability of nonaxially sym metric perturbations. It is shown that the stability criterion derived for gaseous disks is valid for disks rotating within a spheroidal com ponent (as in spiral galaxies) or in the field of a central mass (plan etary rings and accretion disks). Stellar disks are stabilized with si gnificantly greater difficulty. This is attributable mainly to the ani sotropy of the velocity distribution inherent to them, which is favora ble for instability. (C) 1997 American Institute of Physics.