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a binary star system in which one star periodically blocks the light from the other
a star cluster that has a loose, disorganized appearance and contains no more than a few thousands
a huge group of single stars, star systems, star clusters, dust, and gas bound together by gravity
a galaxy with a bulge in the middle and arms that spiral outward in a pinwheel pattern
a galaxy shaped like a round or flattened ball, generally containing only old stars
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