Cataclysmic variable star system. Computer artwork showing atmospheric matter being drawn from one star (centre) by the powerful magnetic field of a white dwarf star at the centre of a neighbouring galaxy (upper left). Systems such as this produce novae, sudden and massive increases in the brightness of the system. This occurs as gas in the matter pulled from the donor star builds up and ignites on the surface of the white dwarf star. These novae events can recur regularly.