What Drives Star Formation?

Abstract

Understanding star formation is one of the outstanding challenges of modern astrophysics. However, in spite of significant progress in recent years, there remain unanswered fundamental questions about the basic physics of star formation. In particular, what drives the star formation process? The prevailing view has been that self-gravitating clouds are supported against collapse by magnetic fields, with ambipolar diffusion reducing support in cores and hence driving star formation, e.g., [8]. The other extreme is that molecular clouds are intermittent phenomena in an interstellar medium dominated by turbulence, and the problem of cloud support for long time periods is irrelevant, e.g., [7]. Clouds form and disperse by the operation of compressible turbulence, with clumps sometimes becoming gravitationally bound. Turbulence then dissipates rapidly, and the cores collapse to form stars. Hence, there are two competing models for driving the star formation process. The issue of what drives star formation is far from settled, on either observational or theoretical grounds. In this contribution we discuss how observations of magnetic fields in molecular clouds can distinguish between and test these models.