The decaying remnant of a star that has exhausted all available sources of nuclear fusion. White dwarfs
are typically just a few times greater in diameter than the Earth, and are composed of so-called 'degenerate' matter
(an unusual state in which atomic nuclei and electrons exist independently of one another). A white dwarf has no internal energy source, and will eventually
lose what energy it has, becoming completely a dead star known as a black dwarf.