Viscosity in Selfgravitating Accretion Disks

We show that the standard model for geometrically thin accretion disks (α-disks) leads to inconsistencies if selfgravity plays a role. This problem arises from the parametrization of viscosity in terms of local sound velocity and vertical disk scale height. A viscosity prescription based on turbulent flows at the critical effective Reynolds number allows for consistent models of thin selfgravitating disks, and recovers the α-disk solution as the limiting case of negligible selfgravity. We suggest that such selfgravitating disks may explain the observed spectra of protoplanetary disks and yield a natural explanation for the radial motions inferred from the observed metallicity gradients in disk galaxies. Subject headings: accretion, accretion disks — Galaxy: evolution — galaxies: evolution — hydrodynamics — stars: pre-main sequence — turbulence also at: Max-Planck-Institut für Radioastronomie, Bonn, Germany