The high mass density of white dwarfs was demonstrated in 1925 by American astronomer Walter Adams when he measured the gravitational redshift of Sirius B as 21 km/s. In 1926, British astrophysicist Ralph Fowler used the new theory of quantum mechanics to show that these stars are supported by electron gas in a degenerate state. British astrophysicist Leon Mestel demonstrated in 1952 that the energy they emit is the surviving heat from byegone nuclear fusion. He showed that the latter no longer occurs within a white dwarf, and calculated the internal temperature of van Maanen 2 as . He gave a preliminary age estimate of 1011/"A" years, where "A" is the mean atomic weight of the nuclei in the star.