A variable star that shows a sudden and dramatic change in brightness, including flare
stars, novae, and some types of symbiotic stars. They are believed to be very close
binary systems consisting of an accreting white dwarf primary and an evolved late-type
secondary star that has filled its Roche lobe. For systems with an accretion disk,
it is believed that a thermal instability is the cause of repetitive outbursts observed
in cataclysmic variables called dwarf novae.
