CNO Cycle

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Fusion process in stars contaminated by “metals,” specifically carbon (C), nitrogen (N), and oxygen (O). The two branches of the CNO process cycle through a sequence that converts the elements carbon, nitrogen, and oxygen into each other’s isotopes. The first cycle (shown) starts and ends with 12C, which may be considered a catalyst. For abundances characteristic of the Sun, the CNO cycle becomes important for core temperatures of roughly 15 million degrees (1.3 keV), and it provides virtually all of the conversion of 1H into 4He above 25 million degrees (2.2 keV).

Some or all content above used with permission from J. H. Wittke.

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