White dwarfs can be used as galactic chronometers and, therefore, provide important information about galactic evolution if good theoretical models of their cooling are available. Consequently, it is natural to wonder if all the sources or sinks of energy are correctly taken into account. One of these sources is partial differentiation of the chemical components of the white dwarf upon crystallization. In this paper we use a new formalism to show that if there is a redistribution of the elements inside the star, there is a net release of energy that has to be radiated away and that slows down the cooling rate of the white dwarf.

Accepted for publication in ApJ (16 pages, 1 figure, aasms4)