LONG BEACH, CALIFORNIA—Astronomers have identified the largest spiral galaxy known. Spanning well over half a million light-years, NGC 6872 (seen in white and pink in this image acquired with the European Very Large Telescope) is at least five times the size of our own Milky Way, astronomers reported here on Thursday at the 221st meeting of the American Astronomical Society. The galaxy's distorted shape is largely due to its interaction with a smaller companion, IC 4970, seen here just above the main galaxy's core. Both are about 210 million light-years away. New ultraviolet observations with NASA's Galaxy Evolution Explorer (the UV radiation is coded blue in this composite image) revealed a new, young galaxy at the tip of the northeastern arm (upper left), which is not visible in the optical image. This so-called tidal dwarf galaxy probably formed as a result of the encounter of the two larger systems. Studying interacting galaxies like these will shed light on the way new stars can be formed well outside a normal galactic environment, the researchers said.
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