Origin of Bipolar Flows
The strong wind blowing from young stars is not completely understood. One idea
is that it is caused by the matter drawing a magnetic field inward as it falls into the
accretion disk. The escaping wind is partially blocked by the accretion disk around the equator
of the forming star and so escapes along the polar axis, thus producing bipolar outflows from
the young star.
However, this simple picture cannot explain the evidence for the rather
narrow width of the outflow observed in some cases. Presumably
the full mechanism is more complex, perhaps
involving the effect of magnetic fields to focus the ejected material.