Bipolar outflow

Indeed, the bow shocks are thought to sweep up or "entrain" dense gas from the surrounding cloud to form the bipolar outflow.

The presence of a bipolar outflow shows that the central star is still accumulating material from the surrounding cloud via an accretion disk.

The outflow relieves the build-up of angular momentum as material spirals down onto the central star through the accretion disk.

[2][3] Large spectroscopic radial velocity monitoring campaigns have revealed the presence of high-velocity outflows or jets from post-AGB stars.

The presence of a magnetic field causes the eventual ejection and collimation of the matter, forming a bipolar outflow or jet.

Massive galactic molecular outflows may have the physical conditions such as high gas densities to form stars.

The Boomerang Nebula is an excellent example of a bipolar outflow. Image credit: NASA, STScI.
Infrared image of a bipolar outflow. The outflow is driven by a massive young star that was first identified as a radio source and catalogued " DR 21 ". The outflow itself is known as the DR21 outflow, or MHO 898/899. Image credit: Chris Davis, UKIRT/Joint Astronomy Centre