| 单词 | galaxy cluster |
| 释义 | galaxy cluster A group of galaxies containing many hundreds of members extending over a radius of up to a few megaparsecs (there also exist small groups of galaxies, such as the Local Group, with a few tens of members). The richest and most regular clusters, such as the Coma cluster , with thousands of members, are gravitationally bound systems; it is not certain whether other less regular and less concentrated clusters are also bound. As well as galaxies, the clusters contain hot intracluster gas , at temperatures between 107 and 108 K; this can be detected by its X-ray emission. On a scale larger than clusters there are also superclusters , with extents of the order of a hundred megaparsecs, containing about a hundred galaxies. It is not known whether superclusters are gravitationally bound. See also missing mass |
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