This is an important step in the evolution and growth of many galaxies. Occasionally, galaxies slam into one another, merging their stars and dust together. The Milky Way lies within the cluster known as the Local Group, which only contains 50 galaxies. Some clusters are large, containing over a thousand galaxies while others are much smaller. Galaxies don't float through space in isolation but are bunched together in groups known as clusters. (Image credit: NASA, ESA, and the Hubble Heritage Team (STScI/AURA)) When galaxies collide Also known as the Southern Pinwheel, M83 is located 15 million light-years away in the constellation Hydra. The magentas and blues indicate star-forming regions. This Hubble Space Telescope image shows the full beauty of nearby spiral galaxy M83 in a mosaic of many photos stitched together. Collisions or close calls with other galaxies can also deform their shapes. The gravity of other galaxies has often affected them, stretching them out or warping them. They are neither round nor boast spiral arms, and their shapes lack specific definition. The remaining 3 percent of the galaxies in the universe are known as irregular galaxies. Although they make up a smaller portion of the visible galaxies, astronomers think that over half the galaxies in the universe are elliptical. Elliptical galaxies have less dust than their spiral counterparts, and so the star-making process has all but ended. Their appearance ranges from circular to very stretched out. The dust and gas in spiral galaxies are consistently fueling the formation of new stars.Įlliptical galaxies lack the spiral arms of their more flamboyant cousins. Some, known as "barred spirals," have a bar structure in their center, formed by dust and gas funneled into the center. The gas and dust in a spiral galaxy circles the center at speeds of hundreds of miles per second, creating their pinwheel shape. Known as spiral galaxies, these groups make up most of the galaxies that astronomers can see. Some, like the Milky Way, have arms spiraling outward around their center. Each type has different characteristics and a different history of evolution. Other galaxies may contain quasars - the most energetic bodies in the universe - at their core. Material circling the black hole may be accelerated outward by its jets. In some cases, a galaxy’s central black hole is extremely large or active, even in relatively small galaxies. Most galaxies have black holes at their centers that can produce a tremendous amount of energy, which astronomers can see over great distances.
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