Radiation-driven warping: The origin of warps and precession in accretion disks

A geometrically thin, optically thick, warped accretion disk with a central source of luminosity is subject to nonaxisymmetric forces due to radiation pressure; the resulting torque acts to modify the warp. In a recent paper, J.E. Pringle used a local analysis to show that initially planar accretion disks are unstable to warping that is driven by radiation torque. Here we extend this work with a global analysis of the stable and unstable modes. We confirm Pringle's conclusion that thin, centrally illuminated accretion disks are generically unstable to warping via this mechanism; we discuss the time evolution and likely steady state of such systems, and show specifically that this mechanism can explain the warping of the disk of water masers in NGC 4258 and the 164 day precession period of the accretion disk in SS 433. Radiation-driven warping and precession provide a robust mechanism for producing warped, precessing accretion disks in active galactic nuclei and X-ray binary systems.