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 consistent with recent re-analysis by \citeasnoun{RZa99} of experimental results on turbulent Couette-Taylor flows. This new beta -viscosity formulation is applied to both selfgravitating and non-selfgravitating disks and is shown to yield the standard alpha -disk prescription in the case of shock dissipation limited, non-selfgravitating disks. A specific case of fully selfgravitating beta -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 beta -mechanism may also account for the rapid mass transport required to power ultra luminous infrared galaxies.