Evidence for colliding stellar winds in the Cyg OB2 #9 binary system was only found as the two stars neared the closest point on their 2.4-year orbit around each other. As the stars approach each other the fierce stellar winds slammed together at speeds of several million kilometres per hour, generating hot plasma at a million degrees which then shone brightly in X-rays. The emission falls away as the two stars move away from each other.

The animation begins by tracing the orbits of the two stars, before presenting X-ray data from ESA’s XMM-Newton and NASA’s Swift space telescopes during observing opportunities of Cyg OB2 #9 in 2011. The corresponding positions of the stars along their orbits are illustrated in the animation inset.

Credits: NASA Goddard Space Flight Center