Angular Momentum Transport in Protostellar Disks

Abstract

Analyses of angular momentum transport in protoplanetary disks are important for the investigation of star formation as well as the origin of the solar system. During the formation stages, the disk dynamics are regulated by mixing of infalling material and disk gas. In the outermost regions of the disk, self, gravity may promote thegrowth of non axisymmetric perturbations and the associated tidal torque can provide an effective angular momentum transfer mechanism. After infall is switched off, convectively driven turbulence provides an effective angular momentum transfer which yields an evolutionary timescale of the order 10^5–6 y. Convection in protoplanetary disks may eventually be stabilized by surface heating. When the grains in the disk settle into the midplane region, the disk can neither generate its own energy through viscous dissipation nor reflect radiation from the central star. Consequently, the infrared excess vanishes and the young stellar objects become “naked T Tauri stars.” Protoplanetary formation modifies the structure and evolution of the disk when protogiant planets acquire sufficient mass to truncate the disk. In this case, a protoplanet’s tidal torque induces the opening of a gap in the vicinity of the protoplanet’s orbit. Gap formation also leads to the termination of protoplanetary growth by accretion. The condition for proto-Jupiter to acquire its present mass implies that the viscous evolution timescale for the disk to be comparable to the age of typical T Tauri stars with circumstellar protoplanetary disks.