 Accretion-disk self-gravity

Accretion-disk self-gravity is the contribution of the disk's own matter to its gravitational field. A low total disk mass can still matter for local vertical confinement or the growth of density disturbances. The Toomre parameter compares gravity with pressure and rotation, but instability does not guarantee fragmentation: heating by gravitationally driven motions can balance cooling. Local numerical experiments distinguish that regulated state from breakup when cooling is sufficiently rapid.^[ref]