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Universe of the Hubble Space Telescope 2001 Calendar

Hickson compact group 87 or HCG 87 is a compact group of four galaxies bound together by their mutual gravitational attraction some 400 million light years distant toward the constellation Capricornus. Two of the galaxies­­galaxy 87a, the edge-on spiral galaxy at the bottom of the image, and galaxy 87b, the elliptical galaxy above and to the right of galaxy 87a­­contain active galactic nuclei, which are thought to harbor massive black holes. Another of the galaxies­­galaxy 87c, the spiral galaxy above 87a­­is undergoing a burst of intense star formation. Gravitational interaction between galaxies is thought to trigger star formation activity. Astronomers believe that the galaxies that make up HCG 87 will eventually merge to form a single bright elliptical galaxy.