English: Whirlpool Galaxy (M51a) is an interacting grand-design spiral galaxy 23 million ly away in the constellation Canes Venatici - 40% the size of the Milky Way (76,000 ly) - Seyfert 2 active galactic nucleus contains a black hole partially occluded by dust - Pronounced spiral structure is believed to be the result of its companion galaxy (NGC 5195) having passed through the main disk 550 million years ago -
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