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Superclusters are large groups of smaller galaxy clusters or galaxy groups and are among the largest known structures of the cosmos. The Milky Way is in the Local Group of galaxies, which in turn is in the Laniakea Supercluster.〔(Earth's new address: 'Solar System, Milky Way, Laniakea' / Nature )〕 This supercluster spans over 500 million light years, while the Local Group spans over 10 million light years.〔http://www.universetoday.com/30286/local-group/〕 The number of superclusters in the observable universe is estimated to 10 million.〔http://www.atlasoftheuniverse.com/universe.html〕 Galaxies are grouped into clusters instead of being dispersed randomly. Clusters of galaxies are grouped together to form superclusters. Typically, superclusters contain dozens of individual clusters throughout an area of space about 150 million lightyears across. Unlike clusters, superclusters are not bound together by gravity. They are all shifting away from each other due to the Hubble flow. Our galaxy falls within the Local Group, which is a poor and irregular cluster of galaxies. Poor clusters may contain only a few dozen galaxies as compared to rich clusters that can contain hundreds or even thousands. The Local Group is near the Local Supercluster (also known as the Virgo Supercluster) which has a diameter of 100 million lightyears. The Local Supercluster contains a total of about 1015 times the mass of the Sun. The biggest cluster in the local universe is called the Great Attractor. Its gravity is so strong that the Local Supercluster, including the Milky Way, is moving in a direction towards it at a rate of several hundred kilometers per second. The biggest supercluster outside of the local universe is the Perseus-Pegasus Filament. It contains the Perseus supercluster and it spans about a billion light years. From what we currently know, it is the largest structure in the universe. This supercluster was discovered by David Batuski and Jack Burns of New Mexico State University. ==Distribution: cosmic voids and sheets== Research has been done to try to understand the way in which superclusters are arranged in space. Maps are used to display the positions of 1.6 million galaxies. Three-dimensional maps are used to further understand the positions of these superclusters. In order to map them three-dimensionally, the position of the galaxy in the sky as well as the galaxy's redshift are used for calculation. The galaxy's redshift is used with the Hubble Law in order to determine its position in three-dimensional space. It was discovered from those maps that superclusters of galaxies are not spread uniformly across the universe but they seem to lie along filaments. Maps reveal huge voids where there are extremely few galaxies. Some dim galaxies or hydrogen clouds can be found in some voids, but most galaxies are found in sheets between the voids. The voids themselves are often spherical but the superclusters are not. They can range from being 100 million to 400 million lightyears in diameter.The pattern of sheets and voids contains information about how galaxy clusters formed in the early universe. There is a sponge analogy used often that compares a sponge to the pattern of clusters of galaxies in the universe – the holes are the voids and the other parts are the locations of the superclusters. 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「supercluster」の詳細全文を読む スポンサード リンク
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