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Westerlund 2 is an obscured compact young star cluster (perhaps even a super star cluster) in the Milky Way, with an estimated age of about one or two million years. It contains some of the hottest, brightest, and most massive stars known. The cluster resides inside a stellar breeding ground known as Gum 29, located 20,000 light-years away in the constellation Carina.〔(【引用サイトリンク】url=http://hubblesite.org/newscenter/archive/releases/2015/12/ )〕 ==Cluster members== The cluster contains at least a dozen O stars, of which at least three are eclipsing binaries. All are hotter than 38,000K and more luminous than . Several Wolf–Rayet stars are found in the vicinity of Westerlund 2, although not in the central core. WR20a, a binary consisting of two WR stars, and the single stars WR20aa, WR20b, and WR20c are all thought to be members of the cluster, although possibly now runaway members. All five Wolf Rayets are extremely young massive objects with OIf */WN spectral types, amongst the most luminous stars in the galaxy. This composite spectral type indicates young very massive hydrogen-burning stars that are just starting to convect nitrogen and helium to the surface and develop denser stellar winds so that they show the emission lines of a Wolf-Rayet star. WR21a, itself a massive binary, lies in the same direction but is unlikely to be a member of Westerlund 2. Westerlund 2 also contains a large number of pre-main sequence stars with masses below . These stars constrain the age of the cluster to near 2 Myr. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Westerlund 2」の詳細全文を読む スポンサード リンク
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