When stars like our Sun have burnt themselves out, they shed their skins to leave behind a dead core. These stellar remnants are white dwarfs, pint-sized objects that are quite unlike any other. No bigger than Earth in diameter, they’re white-hot and slowly cooling as they fade away over billions and trillions of years. Eventually they become stellar ghosts – mere shadows of their former selves. 97 per cent of stars in the universe will one day turn into white dwarfs. In the cosmos’ far future you would be hard-pressed to find a star that’s burning with the aid of fusion, as the universe becomes littered with stellar corpses.
White dwarfs are made by stars that are under eight times the mass of the Sun. Stars that are any larger explode as supernovae, instead leaving behind a dark neutron star or an even darker ravenous black hole. In contrast, white dwarfs are fiery members of the stellar underworld, with temperatures over 200,000 degrees Celsius (360,000 degrees Fahrenheit) when they’re born. But if they’re dead, how can they be so hot? Astronomers believe that they get their incandescent heat because they used to be the cores of stars – the industrious powerhouses where lighter elements are burned and transformed into something heavier.
When a star is created in a nebula, it collects hydrogen gas with its gravity until the gaseous ball of the star is both hot and dense enough to erupt into life. Intense heat and light burst from its centre, driven by nuclear fusion reactions that turn
