Stellar nucleosynthesis

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Stellar nucleosynthesis is the collective term for the nuclear reactions taking place in stars to build the nuclei of the heavier elements. (For other such processes, see nucleosynthesis.)

The processes involved began to be understood early in the twentieth century, when it was first realised that the energy released from nuclear reactions accounted for the longevity of the Sun as a source of heat and light. The prime energy producer in the sun is the fusion of hydrogen to helium, which occurs at a minimum temperature of 3 million kelvin.

Contents 1 History 2 Key reactions 3 References 4 External links

[edit] History

Nucleosynthesis

Stellar nucleosynthesis Big Bang nucleosynthesis Supernova nucleosynthesis Cosmic ray spallation

Related topics

Astrophysics Nuclear fusion R-process S-process Nuclear fission

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In 1920, 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 fusion of hydrogen to form helium. In 1928, George Gamow derived 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 force to 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 Bethe analyzed 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 Weizsäcker in 1938, is most important in more massive stars.

Later, many important details were added to Bethe's theory, like the publication of a celebrated paper in 1957 by Burbidge, Burbidge, Fowler and Hoyle (commonly referred to as the B²FH paper). This latter work collected and refined earlier researches into a coherent picture that accounted for the observed relative abundances of the elements.

[edit] Key reactions

Nuclear processes

Radioactive decay processes Alpha decay Beta decay Cluster decay Double beta decay Double electron capture Electron capture Gamma radiation Internal conversion Isomeric transition Neutron emission Positron emission Proton emission Spontaneous fission Nucleosynthesis Nuclear fusion Proton-proton chain reaction CNO cycle Triple alpha process Carbon burning process Neon burning process Oxygen burning process Silicon burning process Neutron capture The R-process The S-process Proton capture: The P-process The Rp-process Spallation

The most important reactions in stellar nucleosynthesis are:

• Hydrogen burning:
  • The proton-proton chain
  • The carbon-nitrogen-oxygen cycle
• Helium burning:
  • The triple-alpha process
  • The alpha process
• Burning of heavier elements:
  • Carbon burning process
  • Neon burning process
  • Oxygen burning process
  • Silicon burning process
• Production of elements heavier than iron:
  • Neutron capture:
    • The R-process
    • The S-process
  • Proton capture:
    • The P-process

[edit] References

• H. A. Bethe, Energy Production in Stars, Phys. Rev. 55 (1939) 103; online edition (subscription needed)
• H. A. Bethe, Energy Production in Stars, Phys. Rev. 55 (1939) 434-456; online edition (subscription needed)
• E. Margaret Burbidge, G. R. Burbidge, William A. Fowler, F. Hoyle (1957). "Synthesis of the Elements in Stars". Reviews of Modern Physics 29 (4): 547-650.
• Alak K. Ray (2004) Stars as thermonuclear reactors: their fuels and ashes (arxiv.org article)
• G. Wallerstein, I. Iben Jr., P. Parker, A.M. Boesgaard, G.M. Hale, A. E. Champagne, C.A. Barnes, F. Käppeler, V.V. Smith, R.D. Hoffman, F.X. Timmes, C. Sneden, R.N. Boyd, B.S. Meyer, D.L. Lambert (1999). "Synthesis of the elements in stars: forty years of progress" (pdf). Reviews of Modern Physics 69 (4): 995-1084. Retrieved on 2006-08-04.
• S. E. Woosley, A. Heger, T. A. Weaver (2002). "The evolution and explosion of massive stars". Reviews of Modern Physics 74 (4): 1015-1071.

[edit] External links

• How the Sun Shines by John N. Bahcall
• Nucleosynthesis in NASA's Cosmicopia