A white dwarf is a small, dense star that is the remnant of a star like our Sun after it has exhausted its nuclear fuel. When such a star runs out of hydrogen, it sheds its outer layers, leaving behind a hot core that gradually cools over time. White dwarfs are typically about the size of Earth but contain a mass comparable to that of the Sun. These stars are primarily composed of carbon and oxygen and are supported against gravitational collapse by electron degeneracy pressure. Eventually, a white dwarf will cool and fade, becoming a cold, dark object known as a black dwarf, although the universe is not old enough for any black dwarfs to exist yet.