Crystallization of White Dwarfs

At the temperatures and densities characteristic of the interiors of the white dwarfs, the ions begin to freeze into a regular lattice structure. On the assumption that the transition to the solid state is a first-order phase change, we show that the release of the latent heat of crystallization is sufficient to slow the rate of cooling of the white dwarfs, with the consequent formation of "crystallizing sequences" in the H-R diagram. Comparison of the theoretically predicted sequences with the two groups of white dwarfs observed by Eggen and Greenstein suggests that stars in the fainter group are the direct descend- ants of the helium-burning red giants, while those in the brighter group are the end product of a more advanced stage of stellar evolution