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NGC 7217 is an unbarred spiral galaxy in the constellation Pegasus. == Features == NGC 7217 is a gas-poor system〔 〕 whose main features are the presence of several rings of stars concentric to its nucleus: three main ones -being the outermost one the most prominent and the one that features most of the gas and star formation of this galaxy-,〔 plus several others inside the innermost one discovered with the help of the Hubble Space Telescope, a feature that suggests NGC 7217's central regions have suffered several starbursts,〔 〕 and a very large and massive spheroid that extends beyond its disk.〔 〕 Other noteworthy features this galaxy has are the presence of a number of stars rotating in the opposite direction around the galaxy's center to most of them〔 〕 and two distinct stellar populations: one of intermediate age on its innermost regions and a younger, metal-poor on its outermost ones.〔 〕 It has been suggested these features were caused by a merger with another galaxy〔 〕 and, in fact, computer simulations show that NGC 7217 could have been a large lenticular galaxy that merged with one or two smaller gas-rich ones of late Hubble type becoming the spiral galaxy we see today.;〔 however right now this galaxy is isolated in space, with no nearby major companions.〔 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 7217」の詳細全文を読む スポンサード リンク
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