The Chemical Composition of the Stars

The usual view that the stars contain at least ten per cent, by mass in the form of heavy elements is inconsistent with data concerning both the composition of interstellar material and the composition of stellar atmospheres. The data suggest that at the time of condensation of the stars at least 99 per cent by mass must be in the form of hydrogen. On this view the mean molecular weight μ at the time of condensation is close to 0.5, and a subsequent increase in μ can only arise from the conversion of hydrogen to helium by thermonuclear reactions. The effect of this on the luminosities of stars is examined, and it is shown that the resulting theory is at least in as good agreement with the observed luminosities as the old theory. It is emphasized that the possibility of a very high hydrogen content has been generally recognized for many years. The new feature of the present work is the argument given in favour of a hitherto neglected alternative.