COSMOLOGICAL ACCRETION DISK EMBEDDED IN BACKGROUND-RADIATION - INTERPLAY OF VISCOSITY AND RADIATION DRAG

The time-evolutionary properties of a standard alpha-type disk under t he influence of a strong radiation field (''beta drag'') is investigat ed. Viscous diffusion tends to transport angular momentum from the inn er portions outward, whereas Compton drag efficiently removes angular momentum at large radii. As a result, both effects reinforce each othe r, promoting a more rapid accretion, compared with those cases in the absence of either of the two processes. The effects of radiation drag can be understood by simple transformations of the radius and time; if the kinematic viscosity varies as nu proportional to tau(a) with a be ing a constant, and if the angular frequency is Omega proportional to tau(-3/2), for example, the surface density evolves as Sigma(tau',t') = e(4 beta t) f(tau',t') with tau' drop tau e(2 beta t) and t' drop (e (n beta t) -1)/(n beta), where f(tau,t) is the Sigma evolution without radiation drag, beta is the reciprocal of the drag timescale, and n = 4 -2a. As a consequence, the disk is exponentially contracting with t ime.