History of Solar System Formation and Evolution Hypotheses - Solar Evolution Hypotheses

Solar Evolution Hypotheses

Attempts to isolate the physical source of the Sun's energy, and thus determine when and how it might ultimately run out, began in the 19th century. At that time, the prevailing scientific view on the source of the Sun's heat was that it was generated by gravitational contraction. In the 1840s, astronomers J. R. Mayer and J. J. Waterson first proposed that the Sun's massive weight causes it to collapse in on itself, generating heat, an idea expounded upon in 1854 by both Hermann von Helmholtz and Lord Kelvin, who further elaborated on the idea by suggesting that heat may also be produced by the impact of meteors onto the Sun's surface. However, the Sun only has enough gravitational potential energy to power its luminosity by this mechanism for about 30 million years—far less than the age of the Earth. (This collapse time is known as the Kelvin–Helmholtz timescale.)

Albert Einstein's development of the theory of relativity in 1905 led to the understanding that nuclear reactions could create new elements from smaller precursors, with the loss of energy. In his treatise Stars and Atoms, Arthur Eddington suggested that pressures and temperatures within stars were great enough for hydrogen nuclei to fuse into helium; a process which could produce the massive amounts of energy required to power the Sun. In 1935, Eddington went further and suggested that other elements might also form within stars. Spectral evidence collected after 1945 showed that the distribution of the commonest chemical elements, carbon, hydrogen, oxygen, nitrogen, neon, iron etc., was fairly uniform across the galaxy. This suggested that these elements had a common origin. A number of anomalies in the proportions hinted at an underlying mechanism for creation. Lead is heavier than gold, but far more common. Hydrogen and helium (elements 1 and 2) are virtually ubiquitous yet lithium and beryllium (elements 3 and 4) are extremely rare.