The Milky Way, like other galaxies in the Universe, harbours many young star clusters and associations that are home to hundreds of thousands of hot and massive young stars known as O and B stars. Cygnus OB2 contains more than 60 O-type stars and about a thousand B-type stars.
Deep observations of Cygnus OB2 using NASA's Chandra X-ray Observatory have detected the X-ray emission from the coronae of young stars in the cluster and have probed how these star factories form and evolve. Of the ~1,700 X-ray sources detected, about 1,450 were thought to be stars in the cluster.
The young stars detected ranged in age from one million to seven million years. The infrared data indicates that a low percentage of the stars have circumstellar disks of dust and gas; even fewer of the disks were found close to the OB stars. OB stars emit intense radiation that causes early destruction of circumstellar disks. There is also evidence that the older population of stars has lost its most massive members to supernovae. A total mass of about 30,000 times the mass of the sun is derived for Cygnus OB2; this is similar the most massive star forming regions in the Milky Way.
The composite image of Cygnus OB2 contains X-rays from Chandra (blue), infrared data from Spitzer (red), and optical data from the Isaac Newton Telescope (orange). The image is 11.8 arcmin across (16 light years).
X-ray: NASA/CXC/SAO/J.Drake et al,
Optical: Univ. of Hertfordshire/INT/IPHAS,