Editing Stellar nucleosynthesis (section)

==History==
[[File:Arthur Stanley Eddington.jpg|250px|right|thumb|In 1920, [[Arthur Eddington]] proposed that stars obtained their energy from [[Nuclear fusion#Stellar reaction chains|nuclear fusion]] of [[hydrogen]] to form [[helium]] and also raised the possibility that the heavier elements are produced in stars.]]
In 1920, [[Arthur Eddington]], on the basis of the precise measurements of atomic masses by [[Francis William Aston|F.W. Aston]] and a preliminary suggestion by [[Jean Perrin]], proposed that stars obtained their energy from [[nuclear fusion]] of [[hydrogen]] to form [[helium]] and raised the possibility that the heavier elements are produced in stars.<ref>
{{cite journal
 |last1=Eddington |first1=A. S.
 |year=1920
 |title=The internal constitution of the stars
 |journal=[[The Observatory (journal)|The Observatory]]
 |volume=43 |issue=1341
 |pages=341–358
 |doi=10.1126/science.52.1341.233
 |pmid=17747682
 |bibcode=1920Obs....43..341E
|url=https://zenodo.org/record/1429642
 }}</ref><ref>
{{cite journal
 |last1=Eddington |first1=A. S.
 |year=1920
 |title=The Internal Constitution of the Stars
 |journal=[[Nature (journal)|Nature]]
 |volume=106 |issue=2653 |pages=233–240
 |bibcode=1920Natur.106...14E
 |doi=10.1038/106014a0
|pmid=17747682
 |url=https://zenodo.org/record/1429642
 |doi-access=free
 }}</ref><ref>
{{cite web
 |last=Selle |first=D.
 |date=October 2012
 |title=Why the Stars Shine
 |url=https://www.astronomyhouston.org/sites/default/files/guidestar/2012October.pdf
 |work=Guidestar
 |pages=6–8
 |publisher=Houston Astronomical Society
 |archive-url=https://web.archive.org/web/20131203024638/http://www.astronomyhouston.org/sites/default/files/guidestar/2012October.pdf
 |archive-date=2013-12-03
 |url-status=live
}}</ref> This was a preliminary step toward the idea of stellar nucleosynthesis. In 1928 [[George Gamow]] derived what is now called the [[Gamow factor]], a [[quantum mechanics|quantum-mechanical]] formula yielding the probability for two contiguous nuclei to overcome the electrostatic [[Coulomb barrier]] between them and approach each other closely enough to undergo nuclear reaction due to the [[strong nuclear force]] which is effective only at very short distances.<ref>Krane, K. S., ''Modern Physics'' ([[Hoboken, New Jersey|Hoboken, NJ]]: [[Wiley (publisher)|Wiley]], 1983), [https://books.google.com/books?id=-x-VDwAAQBAJ&pg=PA410&redir_esc=y#v=onepage&q&f=false p. 410].</ref>{{rp|410}} In the following decade the Gamow factor was used by [[Robert d'Escourt Atkinson]] and [[Fritz Houtermans]] and later by [[Edward Teller]] and Gamow himself to derive the rate at which nuclear reactions would occur at the high temperatures believed to exist in stellar interiors.

In 1939, in a [[Nobel Prize#Nobel lecture|Nobel lecture]] entitled "Energy Production in Stars", [[Hans Bethe]] analyzed the different possibilities for reactions by which hydrogen is fused into helium.<ref>
{{cite journal
 |last1=Bethe |first1=H. A.
 |year=1939
 |title=Energy Production in Stars
 |journal=[[Physical Review]]
 |volume=55 |issue=5 |pages=434–456
 |bibcode=1939PhRv...55..434B
 |doi=10.1103/PhysRev.55.434
|pmid=17835673
 |doi-access=free
 }}</ref> He defined two processes that he believed to be the sources of energy in stars. The first one, the [[proton–proton chain reaction]], is the dominant energy source in stars with masses up to about the mass of the Sun. The second process, the [[CNO cycle|carbon–nitrogen–oxygen cycle]], which was also considered by [[Carl Friedrich von Weizsäcker]] in 1938, is more important in more massive main-sequence stars.<ref>{{cite book|last=Lang|first=K. R.|title=The Life and Death of Stars|year=2013|publisher=Cambridge University Press|isbn=978-1-107-01638-5|page=[https://books.google.com/books?id=MN-UCkUK9pcC&pg=PA167&redir_esc=y#v=onepage&q&f=false 167]}}.</ref>{{rp|167}} These works concerned the energy generation capable of keeping stars hot. A clear physical description of the proton–proton chain and of the CNO cycle appears in a 1968 textbook.<ref>Clayton, D. D. (1968). ''Principles of Stellar Evolution and Nucleosynthesis''. [[University of Chicago Press]]. [https://books.google.com/books?id=8HSGFThnbvkC&pg=PT365&redir_esc=y#v=onepage&q&f=false p. 365].</ref>{{rp|365}} Bethe's two papers did not 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 thermodynamically into [[iron]].<ref name=Hoyle1946>
{{cite journal
 |last=Hoyle |first=F.
 |year=1946
 |title=The synthesis of the elements from hydrogen
 |journal=[[Monthly Notices of the Royal Astronomical Society]]
 |volume=106 |issue=5 |pages=343–383
 |bibcode=1946MNRAS.106..343H
 |doi=10.1093/mnras/106.5.343
|doi-access=free
 }}</ref> Hoyle followed that in 1954 with a paper describing how advanced fusion stages within massive stars would synthesize the elements from carbon to iron in mass.<ref name=Hoyle1954/><ref>
{{cite journal
 |last1=Clayton |first1=D. D.
 |title=History of Science: Hoyle's Equation
 |journal=[[Science (journal)|Science]]
 |year=2007
 |volume=318 |issue=5858 |pages=1876–1877
 |doi=10.1126/science.1151167
|pmid=18096793
 |s2cid=118423007
 }}</ref>

Hoyle's theory was extended to other processes, beginning with the publication of the 1957 review paper "Synthesis of the Elements in Stars" by [[Margaret Burbidge]], [[Geoffrey Burbidge]], [[William Alfred Fowler]] and [[Fred Hoyle]], more commonly referred to as the [[B2FH paper|B<sup>2</sup>FH paper]].<ref name=B2FH/> This review paper collected and refined earlier research into a heavily cited picture that gave promise of accounting for the observed relative abundances of the elements; but it did not itself enlarge Hoyle's 1954 picture for the origin of primary nuclei as much as many assumed, except in the understanding of nucleosynthesis of those elements heavier than iron by neutron capture. Significant improvements were made by [[Alastair G. W. Cameron]] and by [[Donald D. Clayton]]. In 1957 Cameron presented his own independent approach to nucleosynthesis,<ref>{{cite report
 |last=Cameron |first=A. G. W.
 |year=1957
 |title=Stellar Evolution, Nuclear Astrophysics, and Nucleogenesis
 |url=https://fas.org/sgp/eprint/CRL-41.pdf
 |publisher=[[Atomic Energy of Canada Limited]]
 |id=Report CRL-41
}}</ref> informed by Hoyle's example, and introduced computers into time-dependent calculations of evolution of nuclear systems. Clayton calculated the first time-dependent models of the [[S-process|''s''-process]] in 1961<ref>
{{cite journal
 |last1=Clayton |first1=D. D.
 |last2=Fowler |first2=W. A.
 |last3=Hull |first3=T. E.
 |last4=Zimmerman |first4=B. A.
 |year=1961
 |title=Neutron capture chains in heavy element synthesis
 |journal=[[Annals of Physics]]
 |volume=12 |issue=3 |pages=331–408
 |bibcode=1961AnPhy..12..331C
 |doi=10.1016/0003-4916(61)90067-7
}}</ref> and of the [[R-process|''r''-process]] in 1965,<ref name=Seeger1965>
{{cite journal
 |last1=Seeger |first1=P. A.
 |last2=Fowler |first2=W. A.
 |last3=Clayton |first3=D. D.
 |year=1965
 |title=Nucleosynthesis of Heavy Elements by Neutron Capture
 |journal=[[The Astrophysical Journal Supplement Series]]
 |volume=11 |pages=121–126
 |bibcode=1965ApJS...11..121S
 |doi=10.1086/190111
|url=https://tigerprints.clemson.edu/cgi/viewcontent.cgi?article=1307&context=physastro_pubs
 }}</ref> as well as of the burning of silicon into the abundant alpha-particle nuclei and iron-group elements in 1968,<ref name=Bodansky1968a>
{{cite journal
 |last1=Bodansky |first1=D.
 |last2=Clayton |first2=D. D.
 |last3=Fowler |first3=W. A.
 |year=1968
 |title=Nucleosynthesis During Silicon Burning
 |journal=[[Physical Review Letters]]
 |volume=20 |issue=4 |pages=161–164
 |bibcode=1968PhRvL..20..161B
 |doi=10.1103/PhysRevLett.20.161
|url=https://tigerprints.clemson.edu/cgi/viewcontent.cgi?article=1393&context=physastro_pubs
 }}</ref><ref name=Bodansky1968b>
{{cite journal
 |last1=Bodansky |first1=D.
 |last2=Clayton |first2=D. D.
 |last3=Fowler |first3=W. A.
 |year=1968
 |title=Nuclear Quasi-Equilibrium during Silicon Burning
 |journal=[[The Astrophysical Journal Supplement Series]]
 |volume=16 |page=299
 |bibcode=1968ApJS...16..299B
 |doi=10.1086/190176
|url=https://tigerprints.clemson.edu/physastro_pubs/312
 }}</ref> and discovered radiogenic chronologies<ref>
{{cite journal
 |last1=Clayton |first1=D. D.
 |year=1964
 |title=Cosmoradiogenic Chronologies of Nucleosynthesis
 |journal=[[The Astrophysical Journal]]
 |volume=139 |page=637
 |bibcode=1964ApJ...139..637C
 |doi=10.1086/147791
|url=https://tigerprints.clemson.edu/cgi/viewcontent.cgi?article=1305&context=physastro_pubs
 }}</ref> for determining the age of the elements.

[[File:Nucleosynthesis in a star.gif|thumb|Cross section of a [[supergiant]] showing nucleosynthesis and elements formed.]]