Caption, by Tom Chao at Space.com: Galaxy NGC 2403 displays its spiral arms which contain hot young stars, colored blue. Also the arms contain star-formation regions, identifiable by an extended red glow. Spiral arms stem from a wave-like pattern superimposing itself upon the rotation disk of stars, gas and dust that make up a disk galaxy. After freeing themselves from a star-forming region, new stars mingle with the older stars in the disk.
Photo credit: Canada-France-Hawaii Telescope Coelum.