A galaxy is a system of stars, stellar remnants, interstellar gas, dust, and dark matter bound toget

A galaxy is a system of stars, stellar remnants, interstellar gas, dust, and dark matter bound together by gravity.^[1][2] The word is derived from the Greek galaxias (γαλαξίας), meaning 'milky', a reference to the Milky Way galaxy that contains the Solar System. Galaxies, averaging an estimated 100 million stars,^[3] range in size from dwarfs with less than a thousand stars^[4] to the largest galaxies known—supergiants with one hundred trillion stars, each orbiting its galaxy's center of mass. Most of the mass in a typical galaxy is in the form of dark matter, with only a few percent of that mass visible in the form of stars and nebulae. Supermassive black holes are a common feature at the centers of galaxies.