Physics – Nuclear Physics – Nuclear Theory
Scientific paper
Dec 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004jahh....7...65m&link_type=abstract
Journal of Astronomical History and Heritage (ISSN 1440-2807), Vol. 7, No. 2, p. 65 - 73 (2004).
Physics
Nuclear Physics
Nuclear Theory
Eddington, Radiative Transfer, Mass-Luminosity Relation, White Dwarfs, Electron Degeneracy
Scientific paper
In 1920. Eddington pointed to the fusion of four hydrogen atoms into a helium atom as the likely energy source supplying the observed stellar luminosity. In his monumental Internal Constitution of the Stars, he argued that the luminosity could be predicted from the equations of hydrostatic equilibrium and radiative transfer. By means of a draconian approximation, which required the energy ɛ liberated per gram to be effectively uniform through the star, he produced his 'standard model', with the luminosity strongly dependent on the mass. Application of his theory to the observed Main Sequence confirmed this, but required also that the central temperature increase only moderately with mass, implying that ɛ is a strong function of temperature. This was subsequently vindicated by thermonuclear theory, but contradicts his approximation. Later work showed that his Mass-Luminosity relation is really a Mass-Luminosity-Radius relation in disguise, but with only a weak dependence on the radius. Radiative transfer effectively fixes the luminosity, and the energy balance condition fixes the radius. To get agreement with the observed luminosity, stellar material must have a substantial hydrogen content.
Eddington's theory does not apply to the high-density. low-luminosity white dwarf stars. He was delighted at Fowler's application of the Pauli Exclusion Principle to show that even at zero temperature, the effectively free gas of degenerate electrons exerts a pressure able to balance the enormous gravitational force. But he never accepted the Stoner-Anderson-Chandrasekhar relativistic extension, with its prediction of a limiting mass, beyond which no cold body can exist in equilibrium. However, his claim that the Fowler equation of state remained valid at all densities failed to carry conviction: 'relativistic degeneracy' is now an essential part of our picture of stellar evolution, ensuring that we can account for the synthesis of the more massive elements, the occurrence of supernovae, the formation of neutron stars, and collapse into a black hole state.
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