Stellar Nucleosynthesis Supernova

Stellar Nucleosynthesis Supernova-35
During hydrostatic burning these fuels synthesize overwhelmingly the alpha-nucleus () products. Arnett and his Rice University colleagues demonstrated that the final shock burning would synthesize the non-alpha-nucleus isotopes more effectively than hydrostatic burning was able to do, suggesting that the expected shock-wave nucleosynthesis is an essential component of supernova nucleosynthesis.A rapid final explosive burning is caused by the sudden temperature spike owing to passage of the radially moving shock wave that was launched by the gravitational collapse of the core. Together, shock-wave nucleosynthesis and hydrostatic-burning processes create most of the isotopes of the elements carbon ( (from neon to nickel).Of greatest interest historically has been their synthesis by rapid capture of neutrons during the r-process, reflecting the common belief that supernova cores are likely to provide the necessary conditions.

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Apart from Hydrogen and Helium which are the products of Big Bang nucleosythesis all observed chemical elements heavier that Helium (C, O, …

called metals by astronomers) are synthesised inside stars.

Because Iron is the most bound element, all subsequent reactions will be endothermic (requiring energy supply) and no more energy supply will be provided to support the star against gravitational collapse.

The star enters a runaway phase leading to supernova explosion where heavier elements such as Uranium, Lead and Gold will be synthesised through a combinations of neutron capture and decay processes.

More massive stars burn Hydrogen into Helium through a chain of reactions involving Carbon, Nitrogen and Oxygen (inherited from previous stars) through a process called the .

These 3 elements play the role of a catalyst to synthesise 4 protons into Helium with the same energy outcome as the PP chain.If the star is massive enough this rises the temperature to a level where C .If the star is less massive (about 1 solar mass) it enters the white dwarf degeneracy state.Realize that nuclear fusion in stars can occur with negligible impact on the abundances of the chemical elements.Elements heavier than nickel are comparatively rare owing to the decline with atomic weight of their nuclear binding energies per nucleon, but they too are created in part within supernovae.The latter synthesizes the lightest, most neutron-poor, isotopes of the elements heavier than iron from preexisting heavier isotopes.The theory that nucleosynthesis of the chemical elements occurred primarily during advanced evolution of massive stars was first proposed by Hoyle in 1954, in which he predicted the existence of the excited state in the C nucleus that enables the triple-alpha process to burn resonantly, enabling it to heat the helium cores of stars while synthesizing massive quantities of carbon and oxygen; and he introduced the thermonuclear sequels of carbon-burning synthesizing Ne, Mg and Na and of oxygen-burning synthesizing Si, Al and S.When the core of a star is hot enough, due to gravitational contraction, atoms are stripped off their electrons and collisions between atomic nuclei trigger nuclear reactions: the star establishes its hydrostatic equilibrium by radiating away some of the nuclear energy, hence its specific surface temperature.Nucleosynthesis in main sequence stars involves fusion of 4 Hydrogen nuclei into Helium (He or α-particle) through a chain of reactions called the Proton-Proton chain (as first discovered by Hans Bethe in 1939).Evidence of nucleosynthesis in other stars has been discovered in S-Type stars by Merrill (1952).Population II stars are poor in metals whereas Population I are 2 orders of magnitude richer.


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