"spiral galaxy." YourDictionary, n.d. Web. 11 October 2018. <http://www.yourdictionary.com/spiral-galaxy>.
spiral galaxy. (n.d.). Retrieved October 11th, 2018, from http://www.yourdictionary.com/spiral-galaxy
A galaxy consisting of a rotating flattened disk with a central bulge made up mostly of old stars, from which extend two or more spiral arms made up mostly of younger stars and large amounts of interstellar gas and dust.