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. 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 kelvin (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. The silicon-burning process is extremely brief: for a 25-solar mass star, the period lasts 5 days, compared to a prior 10 million years of hydrogen burning.
Nuclear fusion sequence and silicon photodisintegration
After a star completes the oxygen-burning process, its core is composed primarily of silicon and sulfur. 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. which creates new elements by the alpha process, adding one of these freed alpha particles
During this phase of the contraction, the potential energy of gravitational contraction heats the interior to 5 GK (430 keV), which opposes and delays the contraction. 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. that quickly cools down into a neutron star if the mass of the star is below . Between and , fallback of the material will make the neutron core collapse further into a black hole. 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).
See also
- Alpha nuclide
- Alpha process
- Stellar evolution
- Supernova nucleosynthesis
- Neutron capture:
- p-process
- r-process
- s-process
References
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.