O-type stars are among the most massive and hottest known, pounding their surroundings with intense ultraviolet light and powerful outflows called stellar winds. NASA's Swift and ESA's XMM-Newton X-ray observatories took part in a 2011 campaign to monitor the interaction of two O stars bound together in the same binary system: Cygnus OB2 #9.
Credit: NASA's Goddard Space Flight Center
