White Dwarf
The dense, hot core left behind after a low- or intermediate-mass star expels its outer layers. White dwarfs are composed mostly of electron-degenerate matter and no longer undergo fusion.
Source: chandra.harvard.edu
APODs including "White Dwarf"
The Firework Nebula
04/07/1998
Imaged by the WIYN Telescope, the Firework Nebula is the result of a type of stellar explosion called a nova. In a nova, a nuclear detonation on the surface of a compact white dwarf star blasts away material that has been dumped on its surface by a companion star. Also known as GK Persei or Nova Persei, this nova became one of the brightest stars in the night sky in the year 1901. As it faded, astronomers could see an expanding shell of gas that eventually became this spectacular nebula. While not exactly predictable, GK Per undergoes minor outbursts every three or four years.