![]() ![]() Proton/proton fusion into deuterium accounts for 40% of the reactions by number, releasing 1.44 MeV of energy for each reaction: 10.4% of the Sun's total energy.(Other, much hotter stars have additional pathways available to them, including the CNO cycle, but those all contribute insignificantly in our Sun.) When we take into account the energy liberated in each step, we find: In our Sun, helium-3 fusing with other helium-3 nuclei produces 86% of our helium-4, while the helium-3 fusing with helium-4 through that chain reaction produces the other 14%. More massive stars have additional reactions, like the CNO cycle and other avenues for the proton-proton chain, that dominate at higher temperatures. region of the Universe, we find that only 5% of stars are as massive (or more) than our Sun is. The classification system of stars by color and magnitude is very useful. Because the reactions are both temperature dependent and some of them (like the fusion of two helium nuclei) require multiple examples of proton-proton fusion and deuterium-proton fusion to occur, we have to be careful to account for all of them. In fact, if we look at our Sun, in particular, we can quantify what percentage of energy and of the number of reactions in each step is. Not only are those steps important and frequent, they're more important, energetically, and a greater overall percentage of the reactions than the hydrogen-into-helium reaction. NASA/JPL/Gemini Observatory/AURA/NSFĮverything else either fuses hydrogen into other forms of hydrogen, or helium into other forms of helium. Because deuterium fusion (deuterium+hydrogen=helium-3) occurs at temperatures of just 1,000,000 K, 'failed stars' that don't reach 4,000,000 K get their energy exclusively from the deuterium they're formed with. Only brown dwarfs, like the pair shown here, achieve 100% of their fusion energy by turning hydrogen. Helium-3 fuses with helium-4, producing beryllium-7, which decays and then fuses with another proton (hydrogen-1) to yield two helium-4 nuclei plus energy.Īnd I want you to note something very interesting, and perhaps surprising, about those four possible steps: only step #2, where deuterium and a proton fuse, producing helium-3, is technically the fusion of hydrogen into helium!.Two helium-3 nuclei fuse together, producing helium-4, two protons (hydrogen-1), and energy,.Deuterium (hydrogen-2) and a proton (hydrogen-1) fuse, producing helium-3 and energy,. ![]() Two protons (hydrogen-1) fuse together, producing deuterium (hydrogen-2) and other particles plus energy,.So those are the four possible overall steps available to the components that make up then entire "hydrogen fusing into helium" process in the Sun: In more massive, hotter stars, it can dominate. 14% of the conversion of helium-3 into helium-4 in the Sun. Over time, this can be significant: over its 4.5 billion year lifetime thus far, the Sun has lost approximately the mass of Saturn through this process.Ī higher-energy chain reaction, involving the fusion of helium-3 with helium-4, is responsible for. This occurs because the product of the reaction, helium-4, is lower in mass, by about 0.7%, than the reactants (four hydrogen nuclei) that went into creating it. This fusion reaction, where heavier elements are created out of lighter ones, releases energy owing to Einstein's E = mc 2. Over large amounts of time, hydrogen fuel gets burned through a series of reactions, producing, in the end, large amounts of helium-4. David Malin, UK Schmidt Telescope, DSS, AAOĪll stars, from red dwarfs through the Sun to the most massive supergiants, achieve nuclear fusion in their cores by rising to temperatures of 4,000,000 K or higher. While sun-like stars like our own are considered common, we're actually more massive than 95% of stars in the Universe, with a full 3-out-of-4 stars in Proxima Centauri's 'red dwarf' class. A portion of the digitized sky survey with the nearest star to our Sun, Proxima Centauri, shown in. ![]()
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