The Dumbbell Nebula (M27) in Vulpecula
Two stars of roughly the same mass will evolve in roughly the same manner. But, if one member of a double star is more massive than it's brother, it will spend its nuclear fuel faster, become a red giant sooner and enter into the white dwarf stage while the other is still transforming into a red giant.
The universe is filled with pairs of stars like this- one red giant and the other a white dwarf. When this occurs, the distended glowing atmosphere of the red giant will flow to the dwarf where it can accumulate to ever higher pressures and temperatures. Eventually, a nuclear reaction will ignite the buildup and the white dwarf will briefly flare into brilliance as a nova.
Nova only happen in stellar pairs and represent the aches and pains of older stars. Supernova, however, often occur in single stars and represent the death of one generation and the seeds of the next.
Discovered by Jörg Hanisch of Gescher, Germany and Hans-Goeran Lindberg of Skultuna, Sweden and verified here, a nova was first detected on the evening of August 17-18, 2005 in a stellar pair far beyond but in line of sight with the Dumbbell Nebula.
Pre-nova: July 4-12, 2005
Post-nova: August 21, 2005
Takahashi Mewlon 300, f/9
SBIG ST-10XME, AO-7, CFW8a