A nova can suddenly flares up in brilliance, by a factor of up to about one million, and then, over the next few months or years, fades back more or less to its original luminosity. It appears to be an event that occurs on the surface of a white dwarf in a close binary system when material flowing from the companion star onto the white dwarf's surface undergoes thermonuclear reactions, which trigger a violent explosion. The detonation blows surface material into space, leaving the underlying white dwarf unscathed.
If the mass of the white dwarf is close to the Chandrasekhar limit of 1.4 Msun, hydrogen dragged from its companion burns to helium on its surface. The resulting increase in mass eventually triggers a Type Ia supernova explosion that completely destroys the white dwarf. Figure 08-12a is a recurrent nova in the constellation of Pyxis. It is surrounded by more than 2000 gaseous blobs packed into an area about 1 light year across. The amount of energy released in the nova explosion is around 1037 Joules, while it is about 1044 Joules for the Type Ia supernovae.