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| A Galaxy is composed of gas and dust and stars, billions upon billions of stars, all attracted to each other by gravity. There are over a hundred billion galaxies in the universe. The Milky Way galaxy, a spiral galaxy, is home to our Sun and Earth. We are located on the outer part of one the Milky Way's spiral arms. There are about 20 galaxies in a local area of about several million light years around the Milky Way. A very similar galaxy to ours is M31, Andromeda, which can be seen, on clear nights, with the naked eye from Earth. |
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Globular
Cluster CG1 in M31
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Supernova
in M51
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M100
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| This group of four galaxies is known as the Hickson Compact Group 87 (HCG 87). The Wide-Field and Planetary Camera 2 on the Hubble Telescope (HST) provides a striking improvement in resolution over previous ground based imaging. In particular, this image reveals complex details on the dust lanes of the group's largest galaxy member (HCG 87a), which is actually disk-shaped, but tilted so that we see it nearly edge-on. Both 87a and its elliptically shaped nearest neighbor (87b) have active galactic nuclei which are believed to harbor black holes that are consuming gas. A third group member, the nearby spiral galaxy (87c), may be undergoing a burst of active star formation. Gas flows within galaxies can be intensified by the gravitational tidal fuel for both active nuclei and starburst phenomena. These three galaxies are so close to each other that gravitational forces disrupt their structure and alter their evolution. |
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