ACCRETION FLOWS NEAR BLACK-HOLES MEDIATED BY RADIATIVE VISCOSITY

Angular momentum transport by photons is analyzed for thin and thick configurations of steady accretion flows near black holes. The radiative viscosity coefficient is derived accurately from kinetic theory for arbitrary photon spectra. Thin Keplerian disks cannot be supported by radiative viscosity. However, in a quasi-spherical accretion most of the initial angular momentum of the gas can be transported away by the photons it produces, allowing gas flow toward the central black hole. Nearly spherical accretion may therefore result from more general boundary conditions than usually assumed. Compton drag can also be effective in the outer optically thin part of the flow. The radiative transport of angular momentum may provide the needed accretion to fuel massive black holes in active galactic nuclei.