The Cooling of White Dwarfs and a Varying Gravitational Constant

Within the theoretical framework of some modern unification theories the constants of nature are functions of cosmological time. Since white dwarfs are long-lived, compact objects, they offer the possibility of testing a possible variation of the gravitational constant and, thus, to place constraints to these theories. We present full white dwarf evolutionary calculations in the case in which the gravitational constant G decreases with time. White dwarf evolution is computed in a self-consistent way, including the most up-to-date physical inputs. The evolutionary sequences also consider accurate outer boundary conditions provided by non-gray model atmospheres and a detailed core chemical composition that results from the calculation of the full evolution of progenitor stars. We find that the mechanical structure and the energy balance of the white dwarf are strongly modified by the presence of a varying G. In particular, for a rate of change of G larger than (G) over dot/G = 1 x 10(-12) yr(-1), the evolution of cool white dwarfs is markedly affected. The impact of a varying G is more notorious in the case of more massive white dwarfs.