ĭuring this phase of the contraction, the potential energy of gravitational contraction heats the interior to 5 GK (430 keV) and this opposes and delays the contraction. The star has run out of nuclear fuel and within minutes its core begins to contract. The nickel-56 decays first to cobalt-56 and then to iron-56, with half-lives of 6 and 77 days respectively, but this happens later, because only minutes are available within the core of a massive star. Burning then becomes much more rapid at the elevated temperature and stops only when the rearrangement chain has been converted to nickel-56 or is stopped by supernova ejection and cooling. The silicon-burning sequence lasts about one day before being struck by the shock wave that was launched by the core collapse. Silicon burning proceeds by photodisintegration rearrangement, which creates new elements by the alpha process, adding one of these freed alpha particles (the equivalent of a helium nucleus) per capture step in the following sequence (photoejection of alphas not shown):Īlthough the chain could theoretically continue, steps after nickel-56 are much less exothermic and the temperature is so high that photodisintegration prevents further progress. At these temperatures, silicon and other elements can photodisintegrate, emitting a proton or an alpha particle. If it has sufficiently high mass, it further contracts until its core reaches temperatures in the range of 2.7–3.5 GK (230–300 keV). Nuclear fusion sequence and silicon photodisintegration Īfter a star completes the oxygen-burning process, its core is composed primarily of silicon and sulfur. The star catastrophically collapses and may explode in what is known as a Type II supernova. When a star has completed the silicon-burning phase, no further fusion is possible. Silicon burning begins when gravitational contraction raises the star's core temperature to 2.7–3.5 billion kelvins ( GK). It follows the previous stages of hydrogen, helium, carbon, neon and oxygen burning processes. Silicon burning is the final stage of fusion for massive stars that have run out of the fuels that power them for their long lives in the main sequence on the Hertzsprung–Russell diagram. In astrophysics, silicon burning is a very brief sequence of nuclear fusion reactions that occur in massive stars with a minimum of about 8–11 solar masses. Very brief sequence of nuclear fusion reactions that occur in massive stars
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