  Gravity is scale free. Thus gravity may form similar structures in
self-gravitating systems on different scales. Indeed, observations of the
interstellar medium, spiral disks and cosmic structures, reveal similar
characteristics. The structures in these systems are very lumpy and
inhomogeneous. Moreover some of these structures do not seem to be of random
nature, but obey certain power laws.
  Models of slightly dissipative self-gravitating disks show how such
inhomogeneous structures can be maintained on the kpc-scale. The basic physical
processes in these models are self-gravity, dissipation and differential
rotation. In order to explore the structures resulting from these processes,
local simulations of self-gravitating disks are performed in 2D and 3D. We
observe persistent patterns, formed by transient structures, whose intensity
and morphological characteristic depend on the dissipation rate.
