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Galaxy NGC 3753: Two Spirals in One

Is this one galaxy or two? Analysis of has shown evidence that this seemingly single spiral galaxy is actually the result of the recent collision of two spiral galaxies. The slow motion collision took place over about 100 million years and induced a burst of star formation that has begun to subside. Galaxy NGC 3753 is the largest in a group of seven galaxies known as "Copeland's Septet" or Arp 230 (number 320 in Halton C. Arp's "Atlas of Peculiar Galaxies").