Adam Frank, University of Rochester

Topic: "Star Formation Feedback: Do Stars Practice Birth Control?"  (Video)

ABSTRACT:  The link between turbulence and feedback in star formatting environments and protostellar jets remains controversial. Star forming clouds are highly inefficient with only 10% to 30% of cloud  becoming stars.  In this talk I will present a general overview of how stars may control their own formation  efficiency by feeding energy back into the cloud which created them.

To explore issues of turbulence and feedback from young stars I first present a series of numerical simulations tracking the evolution of transient protostellar jets driven into a turbulent medium. Our simulations show both the effect of turbulence on outflow structures and, conversely, the effect of outflows on the ambient turbulence. We demonstrate how turbulence will lead to strong modifications in jet morphology. More importantly, we demonstrate that individual transient outflows have the capacity to reenergize decaying turbulence. We then explore direct driving of turbulence in molecular clouds by multiple protostellar outflows. Using 3-D numerical simulations we focus on the hydrodynamics of multiple outflows interacting within a parsec scale volume and investigate the extent to which overlapping transient outflows injecting directed energy and momentum can be converted into random turbulent motions. We show that turbulence can readily be sustained by these interactions and show that it is possible to broadly characterize an effective driving scale of the outflows.

We compare the velocity spectrum obtained in our studies to that of isotropically forced hydrodynamic turbulence finding that in outflow driven turbulence a power law is indeed achieved. However we find a steeper spectrum is obtained in outflow driven turbulence models than in isotropically forced simulations. We discuss possible physical mechanisms responsible for these results as well and their implications for turbulence in molecular clouds where outflows will act in concert with other processes such as gravitational collapse.