Galaxy types. Artwork of nine of the common types of galaxy. Galaxies are huge groups of stars under mutual gravitational attraction. At centre is a spiral galaxy with a dense nucleus and faint arms. Along the top, from left to right are: the Andromeda galaxy, a side-on spiral galaxy; a flattened elliptical galaxy, and a tight spiral galaxy with dense arms close to the nucleus. The Sombrero galaxy (centre right), is a spiral with a prominent dust lane. From right to left along the bottom are: a barred spiral, with arms extending from a central bar; a loose spiral with fragmented arms, and an edge-on spiral with a small nucleus. A spherical galaxy is at centre left.