When a very large star runs out of fuel it explodes in a supernova explosion. When a small star like our Sun runs out of fuel it becomes a white dwarf star.
A large number of stars in the universe are in pairs. When one of the stars becomes a white dwarf due to its intense density, it acts like a vacuum and starts sucking hydrogen from the bigger star.
When enough gas builds upon the surface of a white dwarf it triggers a thermonuclear reaction, a Micronova. That can last from 10 hours to half a day.
Credit Mr Scientific