On The Importance Of Outflows For Molecular Clouds and Star Formation

Abstract

Energetic molecular outflows, stellar winds and jets appear to be a common consequence of the formation of stars whose masses are comparable to or greater than that of the sun. The large masses and energies of molecular outflows, in particular, suggest that such activity plays an important, if not fundamental, role in the formation and evolution of a star. Molecular outflows may also have a profound effect on the structure and evolution of molecular clouds. In this contribution I will briefly review the current observational perceptions of the natures of outflows, giant molecular clouds (GMCs), and star formation. In particular, I will describe a recent attempt to obtain an unbiased census of the level of outflow activity in a single GMC: the Mon OBI cloud. CO observations of this GMC indicate extensive outflow activity within its boundaries. One outflow was found for every 3000 M® of molecular gas. At this level of activity it would take fewer than 200 generations of outflows to accelerate the entire mass of the GMC to supersonic velocities, suggesting that outflows may be the source of supersonic turbulence and gravitational support for this cloud, and perhaps other GMCs. The utility of infrared energy distributions for understanding the nature and evolution of young stellar objects will also be discussed. I will describe recent observations that suggest that outflows are initiated by objects in the earliest observable stages of stellar development. Theoretical calculations whose synthesis with these observations leads to a physically coherent and plausible model for the formation and early evolution of low mass stars will be reviewed. In this picture outflows are the critical agent which produces the transition from protostellar to early stellar evolution.