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长城 (天文学).
长城(Galaxy Wall),或译为巨墙,是一个关于宇宙大尺度构造的天文学名词。1989年在天文学家玛格利特·盖勒(Margaret Geller)和约翰·修兹劳(John Huchra)试着标示约一万五千个星系(和地球所在的银河系一样层级的星系)的分布时,发现星系、星系团的分布,即使在大尺度下,也并不是以往所想像的均匀分布,反而连结成条状结构。两位天文学家当时所标示出来的那个天文学长城,离地球的银河系足足有两亿光年之遥。它有五亿光年长、三亿光年宽,并且有一千五百万光年那么厚。
在其他天文学家试着以其他的剖面绘制星系、星系团的分布图时,也发现了相同的疏密不均、具有密集与空洞处的情况,而且目前尚未发现比长城更大的宇宙构造。因此目前一般相信大尺度的宇宙结构为泡状,也就是宇宙空洞结构。
照这些剖面图看来,银河系和本星系群也位于星系团密集处,因此一般预料我们所在的银河系也位于某条长城上(参见巨引源)。然而“本”长城有多长、多宽、多厚,目前却不得而知,因为本长城延伸方向恰好在银河系的隐匿带上,被银河系中大量的宇宙尘和宇宙气体遮挡,以至于无法观测。
关于长城和泡状结构的起源,目前的假设之一和暗物质有关。就像太阳系形成过程中有些气体形成行星、有些则失败而散成小行星或彗星一样,那些泡状“空洞”中的质量可能大规模地形成暗物质而不是星系群,而只有在边缘、也就是泡壁之处的质量有机会大量地形成星系群。
外部链接
- 星系群分布、长城与空洞图:图可以参考,但是下方的图说可能有翻译错误,这张图的半径应该是500 millon也就是五亿光年才对。Local Group的翻译也应该是本星系群而不是本超星系团。
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