Carbon-nitrogen-oxygen cycles

(nuclear physics) A group of nuclear reactions involving the interaction of protons with carbon, nitrogen, and oxygen nuclei; completion of any of the cycles results in the consumption of four protons and the production of a helium-4 nucleus, two positrons, two neutrinos, and energy. Abbreviated CNO cycles.

A group of nuclear reactions that involve capture of protons by carbon, nitrogen, and oxygen nuclei. These cycles are believed to be the source of energy in main-sequence stars which are more massive than the Sun. Completion of any one of the cycles results in consumption of four protons, synthesis of one helium nucleus (⁴He) and two neutrinos, and 26.73 MeV of energy. This energy E reflects the difference in mass m between the four protons and the helium nucleus and is equal to the mass difference times the square of the velocity of light c, as is known from Einstein's statement of mass-energy equivalence, E = mc². Because the nuclear fuel consumed in these processes is hydrogen, they are referred to as hydrogen burning by means of the carbon-nitrogen-oxygen (CNO) cycles.