Generalmente le galassie non sono sole. A causa della mutua attrazione gravitazionale formano gruppi e ammassi composti da poche decine fino a centinaia di galassie. All'interno degli ammassi gli scontri e le fusioni fra galassie non sono affatto rari, con quelle di massa maggiore che attraggono, distorcono e poi inglobano quelle più piccole. La stessa Via Lattea mostra al suo interno o nelle immediate vicinanze ciò che resta di galassie più piccole divorate nel corso dei miliardi di anni della sua storia evolutiva. The process of merging (merging ) and growth is a major factor determining the evolution of galaxies. According to some theoretical models, for example, giant elliptical galaxies are formed through the merger of spiral galaxies. In fact, the center of clusters, there where the density is greater and more galactic frequnti are fighting, it is often dominated by giant elliptical. Instead, it is rare to find isolated galaxies. There is, however successful the Hubble Space Telescope, which took over the giant elliptical galaxy ESO 306-17 at about 500 million light years. In the image the galaxy appears surrounded by a number of other galaxies, however, are at greater distances and are only prospectively nearby. In fact, ESO 306-17 appears completely isolated in space, it is immersed in a sea of \u200b\u200bintergalactic gas. More detailed images of the galaxy show that many globular clusters may be remnants of smaller galaxies, "cannibalized" by ESO 306-17 in the course of its history.
Credit: NASA, ESA and Michael West (ESO)
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