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The Abell 520 galaxy cluster is an unusual structure resulting from a major merger. It has been popularly nicknamed The Train Wreck Cluster,〔(【引用サイトリンク】 ‘Cosmic train wreck’ stumps dark-matter physicists )〕〔(【引用サイトリンク】 Abell 520: Dark Matter Mystery Deepens in Cosmic "Train Wreck" )〕 due to its chaotic structure, and is classified as a Bautz-Morgan type III cluster.〔 It is at a co-moving radial distance of and subtends 25 arcminutes on the sky.〔 At one time, this cluster appeared to present a challenge to prevailing theories about dark matter, as well as most alternative theories of modified gravity, because its dark matter content appeared to be distributed in a way which was very different from the usual pattern, and which did not have a simple explanation based on dark matter that interacts only gravitationally. As a result, at one time it was believed that the distribution of the dark matter was the result of a novel mechanism associated with large scale filaments rather than galaxies. An analysis of the motions of 293 galaxies in the cluster field suggested that Abell 520 was a cluster forming at the crossing of three filaments of the large scale structure. However, more precise observations since this time have shown that the earlier observations were misleading, and that the distribution of dark matter and its ratio to normal matter are very similar to those in galaxies in general, making novel explanations unnecessary. ==See also== * Abell catalogue * Bullet Cluster * List of Abell clusters * List of galaxy clusters 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「Abell 520」の詳細全文を読む スポンサード リンク
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