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"
Methuselah Nebula MWP1
21/10/2010
The lovely, symmetric planetary nebula cataloged as MWP1 lies some 4,500 light-years away in the northern constellation Cygnus the Swan. One of the largest planetary nebulae known, it spans about 15 light-years. Based on its expansion rate the nebula has an age of 150 thousand years, a cosmic blink of an eye in the 10 billion year life of a sun-like star. But planetary nebulae represent a very brief final phase in stellar evolution, as the nebula's central star shrugs off its outer layers to become a hot white dwarf. In fact, planetary nebulae ordinarily only last for 10 to 20 thousand years. As a result, truly ancient MWP1 offers a beautiful challenge to astronomers studying the evolution of its central star.