Changing gravitational constant and white dwarfs

If the gravitational constant decreases with time at a constant rate, there is a maximum possible age and a minimum possible luminosity for each white dwarf mass. White dwarfs older and fainter than these limits would, in the past, have exceeded the white dwarf mass limit and have become supernovae.The rate of change of the gravitational constant G/G= (-7.5 +- 2.7) x 10-11 year-1 recently reported by Van Flandern is compatible with the present values of these age and luminosity limits