Earlier this month, the American Physics Society updated their Online Archive to include all the Physical Review articles as far back as 1893. While we celebrate for the time saved from making photocopies of old, dusty volumes in the back room of the library, this new addition is also good news for literature-surfing enthusiasts. Among the sea of findings is a pair of articles, published in 1939 by Hans Bethe of Cornell University that eventually earned him the Nobel Prize of Physics.

In these papers, Bethe proposed two possible fusion reaction mechanisms that enables stellar energy production. They are as follows:

p + p –> ²H

²H + p –> ³He

This helium-3 nucleus further reacts, resulting in helium-4. A second reaction chain was named the C-N-O cycle. This mechanism uses a small amount of carbon, interacting with nitrogen and oxygen intermediates to produce He nuclei from ejected protons as an end product.

While later experiments confirmed the validity of both of his mechanism proposals, he was incorrect in predicting the reaction prevalent in solar energy production. Bethe concluded that C-N-O cycle is the dominant mechanism by the estimated temperature on the sun at that time, which was an over approximation. Both of Bethe’s proposed mechanisms are accepted in the current astrophysics community, with proton-proton fusion as the main source of solar energy.

This pair of articles marked the beginning of many stellar physics discoveries to come. More detail on Bethe’s theory is available in the new APS online archive!

For more information: Landmarks: What Makes the Star Shine?

Noel

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