THE DEATH OF SUN-LIKE STARS
(with a mass up to 1 1/2 times that of the Sun)

A stars expands as it grows old. As the core runs out of hydrogen and then helium, the core contacts and the outer layers expand, cool, and become less bright; this is a red giant.

After expanding and reaching the enormous red giant phase, the outer layers of the star continue to expand. As this happens, the core contracts; the helium atoms in the core fuse together, forming carbon atoms and releasing energy. The core is now stable since the carbon atoms are not further compressible.

The Egg nebula: a planetary nebula formed a few hundred years ago.

Now the outer layers of the star start to drift off into space, forming a planetary nebula (a planetary nebula has nothing to do with planets).

The star loses most of its mass to the nebula. The star cools and shrinks; it will eventually be only a few thousand miles in diameter!

A White dwarf star: (circled) in the globular cluster M4.

The star is now a white dwarf, a stable star with no nuclear fuel. It radiates its left-over heat for billions of years. When its heat is all dispersed, it will be a cold, dark black dwarf - essentially a dead star (perhaps replete with diamonds, highly compressed carbon).

NOVA
A nova is a white dwarf star that suddenly increases in brightness by several magnitudes. It fades very slowly.

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