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Hydrogen fusion (nuclear fusion of four protons to form a helium-4 nucleus [20]) is the dominant process that generates energy in the cores of main-sequence stars. It is also called "hydrogen burning", which should not be confused with the chemical combustion of hydrogen in an oxidizing atmosphere.
The Sun is a main-sequence star, and, as such, generates its energy by nuclear fusion of hydrogen nuclei into helium. In its core, the Sun fuses 620 million metric tons of hydrogen and makes 616 million metric tons of helium each second. The fusion of lighter elements in stars releases energy and the mass that always accompanies it.
In p–p I, helium-4 is produced by fusing two helium-3 nuclei; the p–p II and p–p III branches fuse 3 He with pre-existing 4 He to form beryllium-7, which undergoes further reactions to produce two helium-4 nuclei. About 99% of the energy output of the sun comes from the various p–p chains, with the other 1% coming from the CNO cycle.
Illustration of a proton–proton chain, from hydrogen forming deuterium, helium-3, and regular helium-4. Nuclear transmutation is the conversion of one chemical element or an isotope into another chemical element. [1] Nuclear transmutation occurs in any process where the number of protons or neutrons in the nucleus of an atom is changed.
Such a graph of the abundances is displayed on a logarithmic scale below, where the dramatically jagged structure is visually suppressed by the many powers of ten spanned in the vertical scale of this graph. Abundances of the chemical elements in the Solar System. Hydrogen and helium are most common, residuals within the paradigm of the Big ...
The internal structure of a main sequence star depends upon the mass of the star. In stars with masses of 0.3–1.5 solar masses (M ☉), including the Sun, hydrogen-to-helium fusion occurs primarily via proton–proton chains, which do not establish a steep temperature gradient. Thus, radiation dominates in the inner portion of solar mass stars.
Arthur Eddington had speculated that the conversion of hydrogen into helium by nuclear fusion could provide the energy required to power stars in 1920. [2] [3] Hans Bethe and Charles L. Critchfield had shown the mechanism for stellar fusion of helium by deriving the proton-proton chain (pp-chain) in 1938. [4]
Supernova nucleosynthesis is the nucleosynthesis of chemical elements in supernova explosions.. In sufficiently massive stars, the nucleosynthesis by fusion of lighter elements into heavier ones occurs during sequential hydrostatic burning processes called helium burning, carbon burning, oxygen burning, and silicon burning, in which the byproducts of one nuclear fuel become, after ...