A Note on Hydrodynamic Viscosity and Selfgravitation in Accretion Disks

We propose a generalized accretion disk viscosity prescription based on hydrodynamically driven turbulence at the critical effective Reynolds number. This approach is con- sistent with recent re-analysis by Richard & Zahn (1999) of experimental results on turbulent Couette-Taylor flows. This new -viscosity formulation is applied to both selfgravitating and non-selfgravitating disks and is shown to yield the stan- dard -disk prescription in the case of shock dissipation limited, non-selfgravitating disks. A specific case of fully selfgravitat- ing -disks is analyzed. We suggest that such 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. The -mechanism may also account for the rapid mass transport required to power ul- tra luminous infrared galaxies.