What Is a Galaxy? | NASA Space Place – NASA Science for …
A galaxy is a gravitationally bound system of stars, stellar remnants, interstellar gas, dust, and dark matter. The word is derived from the Greek galaxias (γαλαξίας), literally "milky", a reference to the Milky Way. Galaxies range in size from dwarfs with just a few hundred million (10 ) stars to giants with one hundred trillion (10 ) stars, each orbiting its galaxy's center of mass.
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