Simulation of colliding wind binary
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. Because WR 22 possesses the stronger stellar wind, a bow shock and wake is formed by the O star as it orbits. The stellar orbits are eccentric, so the separation contracts and expands. Consequently, the conditions in the shocked gas around the O star changes; as the stars near closest approach, the gas cools so effectively that it becomes very clumpy. During closest approach, WR 22's stellar wind is so intense that the region where the winds collide is actually 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 system for exploring wind-wind interactions. Simulations like this are being applied to Cygnus OB2 #9 in support of the recent observational campaign to help unravel the properties of its wind-wind collision.