What is Westerlund 2?
[[File:ESO-The Gum 29 Nebula-phot-37-08-fullres.jpg|thumb|right|270px|The vast stellar nursery [[Gum 29]]. At its centre lies the cluster of young stars Westerlund 2. One object at the bottom of the cluster is a system of two of most massive stars known to astronomers.]] [[Image:Westerlund-2-Cluster-NASA.jpg|right|thumb|270px|Westerlund 2 in X-rays]] '''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 year]]s 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.<ref>Binary stars so close that they eclipse as one passes the other.</ref> There are many very young pre-main sequence stars and two [[Wolf–Rayet star]]s. The core of the cluster contains several examples of rare very hot stars.<ref>Rauw G. ''et al'' 2007. Early-type stars in the core of the young open cluster Westerlund2. ''ArXiv''. [https://arxiv.org/abs/astro-ph/0612622]</ref> 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.<ref>Rauw G. ''et al'' 2004. WR20a: a massive cornerstone binary system comprising two extreme early-type stars. A&A Letters. [https://arxiv.org/abs/astro-ph/0404551] </ref> 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 == {{reflist}} [[Category:Super star clusters]]