Everything about Stellar Nucleosynthesis totally explained
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 realized 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
kelvins.
History
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. These works concerned the energy generation capable of keeping stars hot. They didn't address the creation of heavier nuclei, however. That theory was begun by
Fred Hoyle in 1946 with his argument that a collection of very hot nuclei would assemble into
iron. 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
B²FH paper). 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.
Key reactions
The most important reactions in stellar nucleosynthesis:
- Hydrogen burning:
- Helium burning:
- Burning of heavier elements:
- Production of elements heavier than iron:
- Neutron capture:
- Proton capture:
- Photo-disintegration:
Further Information
Get more info on 'Stellar Nucleosynthesis'.
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