Bipolar outflows

A stellar wind which eminates, by preference, the star's two polar regions rather than all other latitudes. Bipolar outflows often represent significant periods of mass loss in a star's life. They tend to occur during the protostar and pre-main sequence phase and, again, during the red giant phase just before the production of a planetary nebula. It is uncertain whether the bipolar flow is caused by a lack of material being ejected at other stellar latitudes or whether something, such as an accretion disc , blocks the material in the equatorial regions and only allows that which is ejected at the poles to escape. It has also been suggested that magnetic fields may constrain the outflowing material. The outflows carve out cavities in the surrounding interstellar medium and cause reflection nebulae to be produced.