Nova formation. Artwork depicting three stages in the formation of a nova. A nova is a stellar event which causes the star to brighten dramatically as seen from Earth. They are thought to form in close binary star systems such as this. At top, the small, dense, hot white star draws matter to it from the larger orange star by gravitational attraction. This accumulates on the surface of the white star (centre), and is heated by compression and the heat of this star. Eventually, the surrounding layers of matter ignite on the surface of the small star, causing a massive release of energy (bottom frame) which outshines both stars. The process can then begin again in some systems.