Cataclysmic variable binary star system, artwork. A red dwarf star (left) is seen in mutual orbit with a white dwarf star (lower right). An accretion disc (blue) of material, gravitationally pulled from the red dwarf star, can be seen around the white dwarf star. Systems such as this produce novae, sudden and massive increases in the brightness of the system. This occurs as gas in the accretion disc builds up and ignites on the surface of the white dwarf star. These novae events can recur regularly. The red dwarf star is shown with dark patches, called sunspots, on its surface. A white dwarf star is a collapsed star with an intense gravitational field.