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NGC 6791
NGC 6791 is an open star cluster in the Lyra constellation.〔(【引用サイトリンク】 title =SIMBAD query result: NGC 6791 -- Open (galactic) Cluster )〕 It was discovered by Friedrich August Theodor Winnecke in 1853. At roughly 8 billion years old, and with an Iron to Hydrogen abundance ratio that is more than twice that of the Sun, it is one of the oldest and most metal-rich clusters in the Milky Way. This is contrary to the typical rule-of-thumb where older means more metal-poor. Compounded with the fact that it has an unusually high population of stars, ''NGC 6791'' is among the most studied clusters in the sky. ==Age studies== Among the dimmest stars in the cluster are groups of white dwarfs that are 6 billion years old and another group that appear to be 4 billion years old. The ages are out of sync with those of the cluster's normal stars, which are 8 billion years old. This seeming contradiction in age for this cluster has been studied and a solution proposed with age of about 8 billion years.
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「NGC 6791」の詳細全文を読む
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