What is the name of the process by which stars fuse hydrogen via carbon catalysis?

The CNO cycle, in which carbon, nitrogen and oxygen act as catalysts - they participate in the reactions and come out unchanged at the end, while four hydrogen nuclei become helium. It dominates in stars heavier than about 1.3 solar masses; smaller stars including the Sun run mostly on the proton-proton chain, with the CNO cycle contributing about one per cent.

It was worked out independently by Hans Bethe and Carl von Weizsäcker in the late 1930s, and it answered a question that had been open for a century: what keeps the Sun burning. Chemical burning gives a few thousand years and gravitational contraction a few tens of millions, both far too short for the geological record - which was a genuine crisis, and Kelvin used the short figure to argue against Darwin's timescales.

The cycle also has an odd political footnote. Bethe published the mechanism in 1939 and then led the theoretical division at Los Alamos; von Weizsäcker worked on the German nuclear programme. Bethe's Nobel came in 1967, and he spent much of the rest of his life campaigning against the weapons he had helped design, including a letter urging Clinton to halt work on new designs, written at 90.