- Stellar nucleosynthesis
The processes involved began to be understood early in the twentieth century, when it was first realized that the
energyreleased from nuclear reactions accounted for the longevity of the Sunas a source of heatand light. The prime energy producer in the sun is the fusion of hydrogento helium, which occurs at a minimum temperature of 3 million kelvins.
Arthur Eddington, on the basis of the precise measurements of atoms by F.W. Aston, was the first to suggest that stars obtained their energy from nuclear fusionof hydrogento form helium.In 1928, George Gamowderived what is now called the Gamow factor, a quantum-mechanical formula that gave the probability of bringing two nuclei sufficiently close for the strong nuclear forceto overcome the Coulomb barrier.The Gamow factor was used in the decade that followed by Atkinson and Houtermans and later by Gamow himself and Teller to derive the rate at which nuclear reactions would proceed at the high temperatures believed to exist in stellar interiors.
In 1939, in a paper entitled "Energy Production in Stars",
Hans Betheanalyzed the different possibilities for reactions by which hydrogen is fused into helium. He selected two processes that he believed to be the sources of energy in stars. The first one, the proton-proton chain, is the dominant energy source in stars with masses up to about the mass of the Sun. The second process, the carbon-nitrogen-oxygen cycle, which was also considered by Carl Friedrich von Weizsäckerin 1938, is most important in more massive stars. These works concerned the energy generation capable of keeping stars hot. They did not address the creation of heavier nuclei, however. That theory was begun by Fred Hoylein 1946 with his argument that a collection of very hot nuclei would assemble into iron. [cite journal | title=The synthesis of the elements from hydrogen | author = F. Hoyle | journal = Monthly Notices of the Royal Astronomical Society| volume = 106 | pages = 343–383 | year=1946 | url=http://adsabs.harvard.edu/abs/1946MNRAS.106..343H] Hoyle followed that in 1954 with a large paper outlining how advanced fusion stages within stars would synthesize elements between carbon and iron in mass.
Quickly, many important omissions to Hoyle's theory were added, beginning with the publication of a celebrated review paper in 1957 by Burbidge, Burbidge, Fowler and Hoyle (commonly referred to as the
B²FHpaper). [cite journal
title= Synthesis of the Elements in Stars
author= E. M. Burbidge, G. R. Burbidge, W. A. Fowler, F. Hoyle
journal= Reviews of Modern Physics
doi= 10.1103/RevModPhys.29.547] This latter work collected and refined earlier researches into a heavily cited picture that gave promise of accounting for the observed relative abundances of the elements. Significant improvements were created by A. G. W. Cameron and by Donald D. Clayton. Cameron presented his own independent approach (following Hoyle) of nucleosynthesis. He introduced computers into time-dependent calculations of evolution of nuclear systems. Clayton calculated the first time-dependent models of the
S-process, the R-process, the burning of silicon into iron-group elements, and discovered radiogenic chronologies for determining the age of the elements. The entire research field expanded rapidly in the 1970s.
red giantshowing nucleosynthesis and elements formed] The most important reactions in stellar nucleosynthesis:
** The carbon-nitrogen-oxygen cycle
* Burning of heavier elements:
Carbon burning process
Neon burning process
Oxygen burning process
Silicon burning process
* Production of elements heavier than
** Neutron capture:
** Proton capture:
* (subscription needed)
* (subscription needed)
* Alak K. Ray (2004) Stars as thermonuclear reactors: their fuels and ashes [http://arxiv.org/abs/astro-ph/0405568 (arxiv.org article)]
* [http://nobelprize.org/physics/articles/fusion/index.html How the Sun Shines] by
John N. Bahcall
* [http://helios.gsfc.nasa.gov/nucleo.html Nucleosynthesis] in
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