What are White Dwarf Stars?

White dwarfs are dead stars. A single white dwarf contains roughly the mass of our sun in a volume no bigger than our planet. Our sun will become a white dwarf someday. White dwarfs are the hot, dense remnants of long-dead stars. They are the stellar cores left behind after a star has exhausted its fuel supply and blown its bulk of gas and dust into space. These exotic objects mark the final stage of evolution for most stars in the universe – including our sun – and light the way to a deeper understanding of cosmic history.

White dwarfs are born when a star shuts down. A star spends most of its life in a precarious balance between gravity and outward gas pressure. The weight of a couple octillion tons of gas pressing down on the stellar core drives densities and temperatures high enough to ignite nuclear fusion: the fusing together of hydrogen nuclei to form helium. The steady release of thermonuclear energy prevents the star from collapsing on itself.