A galaxy is a vast system of stars, stellar remnants, interstellar gas, dust, and dark matter bound together by gravity. It is derived from the Greek word "galaxias," meaning "milky," which is a reference to the Milky Way galaxy that contains the Solar System. Galaxies can range in size from dwarfs with less than a hundred million stars to supergiants with one hundred trillion stars, and they are categorized according to their visual morphology as elliptical, spiral, or irregular
. According to NASA, a galaxy is a huge collection of gas, dust, and billions of stars and their solar systems, all held together by gravity. The Milky Way, our galaxy, is a large disk-shaped barred-spiral galaxy containing about two hundred billion stars and has a total mass of about six hundred billion times the mass of the Sun
