Astronomy   View all facts   Glossary   Help

physical phenomena > energy source > exothermic fusion process > hydrogen burning

hydrogen burning
subject			fact

hydrogen burning	has next higher temperature reaction helium burning
	has minimum mass 0.08 solar masses
	has product helium
	has catalyst
	has reactant hydrogen
	has definition The fusion of hydrogen into helium and the process by which all main-sequence stars generate energy. Every star born with more than 0.08 solar masses burns hydrogen.
	is a kind of exothermic fusion process
exothermic fusion process	liberates energy
fusion	has antonym fission
	produces energy
	has reaction probability
	has minimum temperature
physical process	has domain physics

Kinds of hydrogen burning :

• carbon cycle (2 kinds, 24 facts) (Bethe-Weizsäcker cycle, CNO cycle) - 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.), 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., 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., Use of carbon and nitrogen as intermediates in the nuclear fusion process of the Sun. Cooler stars undergo the proton-proton cycle.
• proton-proton chain (4 kinds, 31 facts) (p-p chain) - thermonuclear reaction in which two protons collide a very high velocities and combine to form deuteurium, the deuteurium can capture a proton to form tritium and tritium can capture a proton to form helium, A series of thermonuclear reactions in which hydrogen nuclei are transformed into helium nuclei. The temperature and density required are about 10⁷ K and 100 g cm^-3. It is the main source of energy in the Sun, where 10³⁸ of these reactions occur every second. All parts of this reaction have been observed in the laboratory, except for the first step ¹H(p, β⁺v)²D, which occurs only a few times in 10¹² collisions of protons. But the first two reactions provide about one-third of the Sun's total energy release. The p-p chain divides into three main branches: PP I, PP II and PP III., Process of nuclear fusion by which relatively cooler stars produce and radiate energy; hotter stars commonly achieve the same result by means of the carbon-nitrogen cycle., The nuclear sequence by which the Sun and all other main-sequence stars with less than 1.5 solar masses fuse hydrogen into helium., An important nuclear fusion reaction that occurs in stars. It begins with the fusion of two hydrogen nuclei, each of which consists of a single proton.