The term for a star that suddenly increases in brightness is a nova. This astronomical event occurs when a white dwarf star in a binary system accumulates material from its companion star. The accumulated hydrogen ignites in a thermonuclear explosion on the surface of the white dwarf, producing a dramatic increase in brightness that can sometimes outshine entire galaxies. Novae can brighten by several magnitudes in a short period, usually lasting for days to weeks before returning to their original brightness. Scientists study novae to understand stellar evolution and the processes that govern such explosive events.