The flow of material in two opposing directions away from a central source, usually a star. Most young stars go through a violent phase of ejecting material. In some, jets are seen moving away from the star at speeds of many hundreds of kilometres per second. The ejected material sweeps up the surrounding molecular gas into two moving lobes of gas, forming a bipolar molecular outflow. Old stars that have evolved off the main sequence also eject material, and this may produce a bipolar outflow which we observe as a bipolar planetary nebula.
Subjects: Astronomy and Astrophysics.