A stellar explosion occurring in a white dwarf binary system when accumulated hydrogen from a companion star ignites in a thermonuclear runaway reaction on the white dwarf's surface. The explosion causes a dramatic but temporary increase in brightness, typically by 7-16 magnitudes, without destroying the white dwarf.
From Latin 'nova stella' (new star), first used by Tycho Brahe in 1572 to describe what appeared to be a new star. The term reflects historical observations of stars suddenly appearing where none were visible before, though we now know the stars existed but were too faint to see until the explosion.
Novae are like cosmic recycling centers! The white dwarf isn't destroyed by the explosion - it just blows off the accumulated material and starts collecting more from its companion, meaning the same system can produce multiple novae over thousands of years.
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