in 1920, arthur eddington, on the basis of the precise measurements of atomic masses by f.w. aston and a preliminary suggestion by jean perrin, proposed that stars obtained their energy from nuclear fusion of hydrogen to form helium and raised the possibility that the heavier elements are produced in stars. this was a preliminary step toward the idea of stellar nucleosynthesis. in 1928, george gamow derived what is now called the gamow factor, a quantum-mechanical formula that gave the probability of bringing two nuclei sufficiently close for the strong nuclear force to overcome the coulomb barrier. the gamow factor was used in the decade that followed by atkinson and houtermans and later by gamow himself and edward teller to derive the rate at which nuclear reactions would occur at the high temperatures believed to exist in stellar interiors.