A model for mass and momentum transfer at the boundary of outflows from young stellar objects

Numerous stars exhibit large scale mass outflows of various forms. The mass outflows from YSO's in particular exhibit a bipolar outflow geometry. These YSO's are often surrounded by dense circumstellar disks, with bipolar outflows exiting from the rotation axis of the disk. The outflows consist of a narrow, well confined optical jet, which subsequently expands to form large scale cavities within the ISM. At the outflow boundary, material diff"uses into the flow, with a resultant exchange of momentum. The mass and momentum exchange that takes place at the outflow boundary occurs within a viscous boundary and a diffusion boundary.