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NGC 404
NGC 404 is a field galaxy〔 〕 located about 10 million light years away in the constellation Andromeda. It was discovered by William Herschel in 1784, and is visible through small telescopes.〔(Mirach's Ghost (NGC 404) ), ''The Internet Encyclopedia of Science'', David Darling. Accessed on line August 15, 2008.〕 NGC 404 lies just beyond the Local Group and does not appear gravitationally bound to it. It is notable for being within 7 arc-minutes of second magnitude star Mirach, making it a difficult target to observe or photograph and granting it the nickname "Mirach's Ghost".〔〔
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== Physical characteristics ==
NGC 404 is a very isolated dwarf lenticular galaxy, a bit more luminous and smaller than the Small Magellanic Cloud and unlike many other early-type galaxies is very rich in neutral hydrogen, most of it concentrated on a pair of large rings around it. It also has star formation both on its center and on its outermost regions, albeit at a low level
Both the outer gas disk and its star formation are assumed to have been triggered by one or several mergers with smaller galaxies roughly 1 billion years ago〔 and it has been proposed NGC 404 is a former spiral galaxy that was transformed into a lenticular one by that event〔
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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