Silicon burning begins when gravitational contraction raises the star's core temperature to 2.7–3.5 billion kelvins (GK). The exact temperature depends on mass. When a star has completed the silicon-burning phase, no further fusion is possible. The star catastrophically collapses and may explode in what is known as a Type II supernova.
Nuclear fusion sequence and silicon photodisintegrationedit
After a star completes the oxygen-burning process, its core is composed primarily of silicon and sulfur.[2][3] 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). At these temperatures, silicon and other elements can photodisintegrate, emitting a proton or an alpha particle.[2] Silicon burning proceeds by photodisintegration rearrangement,[4] which creates new elements by the alpha process, adding one of these freed alpha particles[2] (the equivalent of a helium nucleus) per capture step in the following sequence (photoejection of alphas not shown):
Although the chain could theoretically continue, steps after nickel-56 are much less exothermic and the temperature is so high that photodisintegration prevents further progress.[2]
The silicon-burning sequence lasts about one day before being struck by the shock wave that was launched by the core collapse. 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 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. The star has run out of nuclear fuel and within minutes its core begins to contract.[citation needed]
During 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.[5] However, since no additional heat energy can be generated via new fusion reactions, the final unopposed contraction rapidly accelerates into a collapse lasting only a few seconds.[6] The central portion of the star is now crushed into a neutron core with the temperature soaring further to 100 GK (8.6 MeV)[7] that quickly cools down[8] into a neutron star if the mass of the star is below 20 M☉.[6] Between 20 M☉ and 40–50 M☉, fallback of the material will make the neutron core collapse further into a black hole.[9] The outer layers of the star are blown off in an explosion known as a Type IIsupernova that lasts days to months. The supernova explosion releases a large burst of neutrons, which may synthesize in about one second roughly half of the supply of elements in the universe that are heavier than iron, via a rapid neutron-capture sequence known as the r-process (where the "r" stands for "rapid" neutron capture).
This graph shows the binding energy per nucleon of various nuclides. The binding energy is the difference between the energy of free protons and neutrons and the energy of the nuclide. If the product or products of a reaction have higher binding energy per nucleon than the reactant or reactants, then the reaction is exothermic (releases energy) and can go forward, though this is valid only for reactions that do not change the number of protons or neutrons (no weak force reactions). As can be seen, light nuclides such as deuterium or helium release large amounts of energy (a big increase in binding energy) when combined to form heavier elements—the process of fusion. Conversely, heavy elements such as uranium release energy when broken into lighter elements—the process of nuclear fission. In stars, rapid nucleosynthesis proceeds by adding helium nuclei (alpha particles) to heavier nuclei. As mentioned above, this process ends around atomic mass 56.[10] Decay of nickel-56 explains the large amount of iron-56 seen in metallic meteorites and the cores of rocky planets.
^Fryer, Chris L. (2003). "Black Hole Formation from Stellar Collapse". Classical and Quantum Gravity. 20 (10): S73–S80. Bibcode:2003CQGra..20S..73F. doi:10.1088/0264-9381/20/10/309. S2CID 122297043. from the original on 2020-10-31. Retrieved 2019-11-29.
^. July 2005. Archived from the original on March 9, 2006. Retrieved January 7, 2007.
External linksedit
Stellar Evolution: The Life and Death of Our Luminous Neighbors, by Arthur Holland and Mark Williams of the University of Michigan
, by Tufts University
Chapter 21: Stellar Explosions, by G. Hermann
Arnett, W. D., Advanced evolution of massive stars. VII – Silicon burning / Astrophysical Journal Supplement Series, vol. 35, Oct. 1977, p. 145–159.
Hix, W. Raphael; Thielemann, Friedrich-Karl (1 April 1996). "Silicon Burning. I. Neutronization and the Physics of Quasi-Equilibrium". The Astrophysical Journal. 460: 869. arXiv:astro-ph/9511088v1. Bibcode:1996ApJ...460..869H. doi:10.1086/177016. S2CID 119422051. Retrieved 29 July 2015.
February 15, 2024
silicon, burning, process, astrophysics, silicon, burning, very, brief, sequence, nuclear, fusion, reactions, that, occur, massive, stars, with, minimum, about, solar, masses, silicon, burning, final, stage, fusion, massive, stars, that, have, fuels, that, pow. In astrophysics silicon burning is a very brief 1 sequence of nuclear fusion reactions that occur in massive stars with a minimum of about 8 11 solar masses 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 It follows the previous stages of hydrogen helium carbon neon and oxygen burning processes Silicon burning begins when gravitational contraction raises the star s core temperature to 2 7 3 5 billion kelvins GK The exact temperature depends on mass When a star has completed the silicon burning phase no further fusion is possible The star catastrophically collapses and may explode in what is known as a Type II supernova Contents 1 Nuclear fusion sequence and silicon photodisintegration 2 Binding energy 3 See also 4 References 5 External linksNuclear fusion sequence and silicon photodisintegration editAfter a star completes the oxygen burning process its core is composed primarily of silicon and sulfur 2 3 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 At these temperatures silicon and other elements can photodisintegrate emitting a proton or an alpha particle 2 Silicon burning proceeds by photodisintegration rearrangement 4 which creates new elements by the alpha process adding one of these freed alpha particles 2 the equivalent of a helium nucleus per capture step in the following sequence photoejection of alphas not shown 2814 Si 42 He 3216 S3216 S 42 He 3618 Ar3618 Ar 42 He 4020 Ca4020 Ca 42 He 4422 Ti4422 Ti 42 He 4824 Cr4824 Cr 42 He 5226 Fe5226 Fe 42 He 5628 NiAlthough the chain could theoretically continue steps after nickel 56 are much less exothermic and the temperature is so high that photodisintegration prevents further progress 2 The silicon burning sequence lasts about one day before being struck by the shock wave that was launched by the core collapse 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 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 The star has run out of nuclear fuel and within minutes its core begins to contract citation needed During 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 5 However since no additional heat energy can be generated via new fusion reactions the final unopposed contraction rapidly accelerates into a collapse lasting only a few seconds 6 The central portion of the star is now crushed into a neutron core with the temperature soaring further to 100 GK 8 6 MeV 7 that quickly cools down 8 into a neutron star if the mass of the star is below 20 M 6 Between 20 M and 40 50 M fallback of the material will make the neutron core collapse further into a black hole 9 The outer layers of the star are blown off in an explosion known as a Type II supernova that lasts days to months The supernova explosion releases a large burst of neutrons which may synthesize in about one second roughly half of the supply of elements in the universe that are heavier than iron via a rapid neutron capture sequence known as the r process where the r stands for rapid neutron capture Binding energy edit nbsp Curve of binding energyMain articles Nuclear binding energy and Iron peak This graph shows the binding energy per nucleon of various nuclides The binding energy is the difference between the energy of free protons and neutrons and the energy of the nuclide If the product or products of a reaction have higher binding energy per nucleon than the reactant or reactants then the reaction is exothermic releases energy and can go forward though this is valid only for reactions that do not change the number of protons or neutrons no weak force reactions As can be seen light nuclides such as deuterium or helium release large amounts of energy a big increase in binding energy when combined to form heavier elements the process of fusion Conversely heavy elements such as uranium release energy when broken into lighter elements the process of nuclear fission In stars rapid nucleosynthesis proceeds by adding helium nuclei alpha particles to heavier nuclei As mentioned above this process ends around atomic mass 56 10 Decay of nickel 56 explains the large amount of iron 56 seen in metallic meteorites and the cores of rocky planets See also editAlpha nuclide Alpha process Stellar evolution Supernova nucleosynthesis Neutron capture p process r process s processReferences edit Woosley S Janka T 2006 The physics of core collapse supernovae Nature Physics 1 3 147 154 arXiv astro ph 0601261 Bibcode 2005NatPh 1 147W CiteSeerX 10 1 1 336 2176 doi 10 1038 nphys172 S2CID 118974639 a b c d Clayton Donald D 1983 Principles of Stellar Evolution and Nucleosynthesis University of Chicago Press pp 519 524 ISBN 9780226109534 Woosley SE Arnett WD Clayton DD Hydrostatic oxygen burning in stars II oxygen burning at balanced power Astrophys J 175 731 1972 Donald D Clayton Principles of stellar evolution and nucleosynthesis Chapter 7 University of Chicago Press 1983 Janka H Th Marek A Martinez Pinedo G Muller B December 4 2006 Theory of core collapse supernovae arXiv astro ph 0612072v1 a b Fryer C L New K C B 2006 01 24 Gravitational Waves from Gravitational Collapse Max Planck Institute for Gravitational Physics Archived from the original on 2006 12 13 Retrieved 2006 12 14 Mann Alfred K 1997 Shadow of a star The neutrino story of Supernova 1987A New York W H Freeman p 122 ISBN 978 0 7167 3097 2 Archived from the original on 2008 05 05 Retrieved 2007 11 19 Bombaci I 1996 The Maximum Mass of a Neutron Star Astronomy and Astrophysics 305 871 877 Bibcode 1996A amp A 305 871B Fryer Chris L 2003 Black Hole Formation from Stellar Collapse Classical and Quantum Gravity 20 10 S73 S80 Bibcode 2003CQGra 20S 73F doi 10 1088 0264 9381 20 10 309 S2CID 122297043 Archived from the original on 2020 10 31 Retrieved 2019 11 29 Mass number number of protons name of isotope mass MeV c 2 binding energy MeV and binding energy per nucleus MeV for different atomic nuclei July 2005 Archived from the original on March 9 2006 Retrieved January 7 2007 External links editStellar Evolution The Life and Death of Our Luminous Neighbors by Arthur Holland and Mark Williams of the University of Michigan The Evolution and Death of Stars by Ian Short Origin of Heavy Elements by Tufts University Chapter 21 Stellar Explosions by G Hermann Arnett W D Advanced evolution of massive stars VII Silicon burning Astrophysical Journal Supplement Series vol 35 Oct 1977 p 145 159 Hix W Raphael Thielemann Friedrich Karl 1 April 1996 Silicon Burning I Neutronization and the Physics of Quasi Equilibrium The Astrophysical Journal 460 869 arXiv astro ph 9511088v1 Bibcode 1996ApJ 460 869H doi 10 1086 177016 S2CID 119422051 Retrieved 29 July 2015 Retrieved from https en wikipedia org w index php title Silicon burning process amp oldid 1176946515, wikipedia, wiki, book, books, library,
