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