Bipolar Flows, Molecular Gas Disks, and the Collapse and Accretion of Rotating Interstellar Clouds

The collapse of rotating interstellar clouds may lead naturally to the formation of flattened molecular gas disks embedded in an extended cloud conducive to the collimation of even an isotropic stellar wind into a bipolar flow. Rigorous numerical models of the collapse and accretion of rotating, axisymmetric, isothermal interstellar clouds are used to verify this hypothesis, for a variety of possible initial clouds. The calculations are relevant for highly evolved clouds containing pre-main-sequence (rather than protostellar) objects. The models demonstrate that in general, rotating interstellar clouds collapse to form a central protostellar core surrounded by a flattened molecular gas disk, perpendicular to an evacuated, bipolar region of remarkable extent and narrowness. An isotropic stellar wind should flow outward preferentially through the previously evacuated bipolar holes.