Galaxy

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A galaxy is a huge collection of gas, dust, and billions of stars and their solar systems, all held together by gravity. Galaxies are formed when vast clouds of gas and dust collapse under their own gravitational pull, allowing stars to form. The word galaxy is derived from the Greek galaxias, literally "milky", a reference to the Milky Way. Galaxies range in size from dwarfs with just a few hundred million stars to giants with one hundred trillion stars, each orbiting its galaxy's center of mass. Most galaxies have a supermassive black hole at their center.

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