The origin of molecular protostellar outflows

We study the geometry of the large scale magnetic field threading the centrifugally supported circumstellar disk that forms in the inner few hundred AU of a dynamically collapsing protostellar molecular cloud core. The disk is highly turbulent, therefore highly diffusive, thus unable by itself to sufficiently stretch and bend the large scale magnetic field so as to launch magnetically driven winds from its surface. However, when we take proper account of the fact that the magnetic field is already highly stretched and bent in the outside dynamically collapsing cloud core, we discover that this contributes to significant outward magnetic field bending around the outer edge of the inner protoplanetary disk too. We obtain the field geometry self-consistently under general simplifying approximations. We also show how this magnetic field geometry leads naturally to strong magneto-centrifugally driven outflows from the surface of the disk, with mass loss rates a significant fraction of the accretion rate onto the inner disk. Our simple picture describes naturally the origin of the molecular winds observed during the end stages of protostellar cloud collapse.