Scientists have combined X-ray data (shown in purple) from NASA's Chandra X-ray Observatory and optical data (shown in white and blue) from the Hubble Space Telescope, the Very Large Telescope, and the Sloan Digital Sky Survey to produce this image of Abell 383, a galaxy cluster 2.3 billion light years away. Abell 383 is 4.84 million light years across and is in the region of the sky marked by the constellation Eridanus. Scientists are studying galaxy clusters -- the largest gravitationally-bound objects in the universe -- in the hopes of better understanding dark matter, whose mass is thought to be five to six times greater than the mass of all the universe's light-emitting matter but is not well understood.

Below, recent Pictures of the Day:

Image: NASA.

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