A
nova (plural or
novas) is a
cataclysmic nuclear explosion on a
white dwarf, which causes a sudden brightening of the star. Novae are not to be confused with other brightening phenomena such as
supernovae or
luminous red novae. Novae are thought to occur on the surface of a white dwarf in a
binary system when they are sufficiently near to one another, allowing material (mostly
hydrogen) to be pulled from the companion star's surface onto the white dwarf. The nova is the result of the rapid fusion of the
accreted hydrogen on the surface of the star, commencing a runaway
fusion reaction.