Westerlund 2

Westerlund 2  is a massive young super star cluster. It is about one or two million years old, and partly obscured with gas. It contains some of the hottest, brightest, and most massive stars known. The cluster is 20,000 light years away in the Milky Way galaxy.

The cluster contains a dozen of O-type main sequence stars, of which at least three are eclipsing binaries.Binary stars so close that they eclipse as one passes the other. There are many very young pre-main sequence stars and two Wolf–Rayet stars.

The core of the cluster contains several examples of rare very hot stars.Rauw G. et al 2007.  Early-type stars in the core of the young open cluster Westerlund2. ArXiv.   Just outside the cluster a massive eclipsing binary WR20a is found at 30 arcseconds (about 1.1 pc in projection), the bright yellow spot just on the lower right side of the cluster center.Rauw G. et al 2004.  WR20a: a massive cornerstone binary system comprising two extreme early-type stars. A&A Letters.  

As its name indicates, the Westerlund 2 cluster was discovered by Bengt Westerlund in the sixties, but its stellar content was assessed only in later years. 

 References 

Category:Super star clusters