This computer simulation shows the gas density around a colliding wind binary named WR 22. The star locations are marked by yellow dots, and decreasing gas density is indicated by the sequence of red, white and blue colours. In this simulation, a 26 solar mass O-type star orbits the hotter and more massive 72 solar mass Wolf-Rayet star WR 22. During closest approach, the more massive star's stellar wind is so intense that the collision region is forced back onto the O star. Such a collapse of the wind region does not occur with Cygnus OB2 #9, which makes it a well-behaved and important example of wind-wind interactions.

Credits: University of Liège/Australian National University/E. R. Parkin and E. Gosset.