Formation and Heating of Molecular Cloud Cores

Abstract

We review the problem of the structure of molecular clouds and its relation to star formation. We discuss why magnetic fields represent the most reasonable candidate for supporting molecular clouds. This picture naturally leads to a theory for the origin of molecular cloud cores, and a conception of “bimodal star formation,” whereby the modes of formation of high-mass stars and low-mass stars are viewed as being fundamentally different on some mechanistic level. Of the two modes of star formation, we examine the low-mass mode in greater detail because of the greater completeness of the developed theory. In particular, we discuss why clumps of molecular gas with the properties of the Taurus complex can naturally be expected to quasistatically develop dense pockets through the slow slippage of ions and field relative to the neutral gas, and why the growing central concentration of each individual dense core can be expected eventually to collapse to form a low mass star plus nebular disk, and, perhaps, stellar or planetary companions. Finally, we examine the role of ambipolar diffusion in heating molecular cloud cores and thereby partially account for the thermal differences between the cores which form low and high mass stars.