Lack of heat in core causes imbalance between pressure and gravity, and core shrinks. Fusion in layer outside core causes outer layers to heat up and the resulting pressure causes the outer layer to expand. Some helium burning at edge of core. Planetary nebula . Looks like a planet in a small telescope.
Stellar core continues to cool and contract.
Black dwarf . Impossible to see in a telescope. Diagrams of clusters of different ages show how the distribution of stars on the H-R diagram changes with time. Return to table of contents. This document was last updated September 1, 1998.