CNO cycle

The CNO cycle (for carbon-nitrogen-oxygen), or sometimes Bethe-Weizsäcker-cycle, is one of two fusion reactions by which stars convert hydrogen to helium, the other being the proton-proton chain.The proton-proton chain is more important in stars the mass of the sun or less. Only 1.7% of 4He nuclei being produced in the Sun are born in the CNO cycle. However theoretical models show that the CNO cycle is the dominant source of energy in heavier stars. The CNO process was proposed by Carl von Weizsäcker and Hans Bethe independently in 1938 and 1939, respectively.
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