Protostellar disk formation and early evolution

This contribution describes the formation of circumstellar disks and their earliest evolutionary phases when self-gravity in the disk plays a crucial role in eliciting the transport of mass and angular momentum. We first disc uss the formation of protostellar disks within the context of analytic infa ll-collapse solutions. We then discuss our efforts to understand the behavi or of the newly formed disks. Our specific approach consists of performing a detailed analysis of a simplified model disk which is susceptible to the growth of a spiral instability. Using a combination of numerical simulation and semi-analytic analysis, we show how the dramatic early phase of mass a nd angular momentum transport in the disk can be explained by a second-orde r nonlinear process involving self-interaction of a dominant two-armed spir al mode.