Silicon-burning process
In
Silicon burning begins when gravitational contraction raises the star's core temperature to 2.7–3.5 billion kelvins (
Nuclear fusion sequence and silicon photodisintegration
After a star completes the
- 28
14Si+ 4
2He
→ 32
16S32
16S+ 4
2He
→ 36
18Ar36
18Ar+ 4
2He
→ 40
20Ca40
20Ca+ 4
2He
→ 44
22Ti44
22Ti+ 4
2He
→ 48
24Cr48
24Cr+ 4
2He
→ 52
26Fe52
26Fe+ 4
2He
→ 56
28Ni
The chain could theoretically continue, as adding further alphas continues to be exothermic all the way to
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
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.[6] 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.[7] The central portion of the star is now crushed into a neutron core with the temperature soaring further to 100 GK (8.6 MeV)[8] that quickly cools down[9] into a neutron star if the mass of the star is below 20 M☉.[7] Between 20 M☉ and 40–50 M☉, fallback of the material will make the neutron core collapse further into a black hole.[10] 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
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
See also
- Alpha nuclide
- Alpha process
- Stellar evolution
- Supernova nucleosynthesis
- Neutron capture:
References
- S2CID 118974639.
- ^ 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)
- .
- 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.
- ISBN 978-0-7167-3097-2. Archived from the originalon 2008-05-05. Retrieved 2007-11-19.
- Bibcode:1996A&A...305..871B.
- 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
- Stellar 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. S2CID 119422051. Retrieved 29 July 2015.