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carbon cycle (Bethe-Weizsäcker cycle, CNO cycle)
subject			fact

carbon cycle	has part product helium
	has part catalyst carbon
	has part catalyst nitrogen
	has part catalyst oxygen
	has part reactant proton
	has reaction 12C(p, γ) 13N(p, γ) 14O(β+ν) 14N(p, γ) 15O(β+ν) 15N(p, α) 12C
	has discovered date 1938
	has minimum mass 1.5 solar masses
	produces energy 26.7 MeV
	has catalyst carbon, nitrogen and oxygen
	has temperature dependence E ∝ T15
	has minimum temperature 15 to 20 million Kelvin
	has synonym Bethe-Weizsäcker cycle
	has synonym CNO cycle
	has definition A series of nuclear reactions in which carbon is used as a catalyst to transform hydrogen into helium. The carbon cycle can take place only if the necessary C and N nuclei are present, and it requires higher temperatures and is far more temperature-dependent than the proton-proton chain. The cycle yields 26.7 MeV of energy. (On the average, 1.7 MeV of this energy is carried away because of neutrino losses.)
	has definition One way that a star converts hydrogen into helium. During the CNO cycle, carbon, nitrogen, and oxygen catalyze the nuclear reaction, so the total number of carbon, nitrogen, and oxygen nuclei remains the same. However, carbon and oxygen gradually get converted into nitrogen. The CNO cycle powers the hydrogen burning that occurs in main-sequence stars with more than 1.5 solar masses and in giants and supergiants of all masses.
	has definition An important nuclear fusion process that occurs in stars. Carbon 12 both initiates it and, following interactions with nuclei of nitrogen, hydrogen, oxygen, and other elements, reappears at its conclusion.
	has definition Use of carbon and nitrogen as intermediates in the nuclear fusion process of the Sun. Cooler stars undergo the proton-proton cycle.
	is a kind of hydrogen burning
hydrogen burning	has next higher temperature reaction helium burning
	has product helium
	has reactant hydrogen
exothermic fusion process	liberates energy
fusion	has antonym fission
	has reaction probability
physical process	has domain physics

Kinds of carbon cycle :

• CNO bi-cycle (3 facts) - Similar to the CNO cycle, except that it also includes a cycle in which the next-to-last step becomes ¹⁵N(p, γ) ¹⁶O(p, γ) ¹⁷F(β⁺ν) ¹⁷O(p, α) ¹⁴N. This reaction occurs once in about 2000 CN cycles. For main-sequence stars greater than a few solar masses, hydrogen burning by the CNO bi-cycle is the main source of energy.
• CNO tri-cycle (2 facts) - Similar to the CNO bi-cycle, with the addition of the cycle ¹⁷O(p, γ) ¹⁸F(β⁺ν) ¹⁸O(p, α) ¹⁵N.

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