By Clara Moskowitz

At the end of a star's lifetime, when it's burned all there is inside it to burn, it often collapses into what's called a white dwarf star. These dense globes have roughly the mass of the sun packed tight into a ball the size of the Earth. Since there is no fuel left for fusion in white dwarfs, they shine only faintly, by emitting stored heat. A white dwarf is thought to be the end stage awaiting most of the stars in our galactic neighborhood, including the sun — only about 3 percent of nearby stars have masses so huge that they collapse even further in supernova explosions.


Blazing Young Dwarf

One of the hottest white dwarfs known to scientists lies in the heart of this nebula, called NGC 2440, about 4,000 light-years from Earth. The star (the bright dot near the photo's center), has a surface temperature of roughly 360,000 degrees Fahrenheit. Since white dwarfs cool as they age, this one must be relatively young. The glowing purple aura around it is the left-over material cast off by the star when it became a white dwarf at the end of its life.