Nova. Artwork of a white dwarf star becoming a nova, as seen from a nearby Saturnlike planet. A nova is a star which suddenly increases in bright ness. White dwarfs are the dim remnants of small to medium sized stars which have run out of hydro gen fuel to power their nuclear reactions. If the white dwarf is in a binary system, it may capture hydrogenrich material from its companion star. This may begin a rapid nuclear reaction on the stars surface. The star typically becomes several thousand times brighter in a matter of hours or days, fading again over months or years. A nova also generally ejects a little of its mass to form a large, gaseous halo.
