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Fusion powers stars and produces virtually all elements in a process called nucleosynthesis. 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 Sun is about halfway through its main-sequence stage, during which nuclear fusion reactions in its core fuse hydrogen into helium. Each second, more than four billion kilograms of matter are converted into energy within the Sun's core, producing neutrinos and solar radiation. At this rate, the Sun has so far converted around 100 times the ...
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.
As a result, there is little mixing of fresh hydrogen into the core or fusion products outward. In higher-mass stars, the dominant energy production process is the CNO cycle, which is a catalytic cycle that uses nuclei of carbon, nitrogen and oxygen as intermediaries and in the end produces a helium nucleus as with the proton–proton chain. [22]
The amounts of total mass in elements heavier than hydrogen and helium (called 'metals' by astrophysicists) remains small (few percent), so that the universe still has approximately the same composition. Stars fuse light elements to heavier ones in their cores, giving off energy in the process known as stellar nucleosynthesis.
Each second, the Sun fuses approximately 600 million tons of hydrogen into helium in a process known as the proton–proton chain (4 hydrogens form 1 helium), converting about 4 million tons of matter to energy. [1] [2] Besides the Sun, other well-known examples of G-type main-sequence stars include Alpha Centauri, Tau Ceti, and 51 Pegasi. [3 ...
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Helium from these hydrogen burning shells drops towards the center of the star and periodically the energy output from the helium shell increases dramatically. This is known as a thermal pulse and they occur towards the end of the asymptotic-giant-branch phase, sometimes even into the post-asymptotic-giant-branch phase.