The B2FH paper, named after the initials of the paper's authors, Margaret Burbidge, Geoffrey Burbidge, William Fowler and Fred Hoyle, is a landmark paper of stellar physics published in Reviews of Modern Physics in 1957. The formal title of the paper is Synthesis of the Elements in Stars, but the article is generally referred to only as "B2FH".
The paper comprehensively outlined and analyzed several key processes that might be responsible for the synthesis of elements in nature and their relative abundance, and is credited with originating what is now the theory of stellar nucleosynthesis.
Physics in 1957
At the time of the publication of the B2FH paper, George Gamow advocated a theory of the universe according to which virtually all elements, or atomic nuclei, were synthesized during the big bang. The implications of Gamow's nucleosynthesis theory (not to be confused with present-day nucleosynthesis theory) is that nuclear abundances in the universe are largely static. Hans Bethe and Charles L. Critchfield had together derived the pp-chain in 1938, and Carl von Weizsäcker and Hans Bethe had independently derived the CNO cycle in 1938 and 1939, respectively, to show that the conversion of hydrogen to helium by nuclear fusion could account for stellar energy production. Thus, it was known by Gamow and others in 1957 that the abundances of hydrogen and helium were not perfectly static. However, at the time, stellar fusion theories did not show how to create any elements heavier than helium, and so Gamow advocated the theory that all elements were residual from the big bang, allowing for slight changes in the ratios of hydrogen and helium. B2FH gave a different account for the origin of heavy elements, suggesting that all atomic nuclei heavier than lithium up to uranium must have been synthesized in stars and not during the big bang. Both theories agree that some light nuclei (hydrogen, and some helium and lithium) were not created in stars, and this led to the now-accepted theory of big bang nucleosynthesis.
Physics in the paper
Because B2FH argued that a majority of all elements except for hydrogen must come from stars, their ideas are called the theory of stellar nucleosynthesis. The key difference between this theory of stellar nucleosynthesis and all previous accounts for the origin of the elements is that B2FH predicted chemical evolution of the universe, which is testable by looking at stellar spectral lines. Quantum mechanics explains why different atoms emit light at characteristic wavelengths, and so by studying the light emitted from different stars, one may infer the atmospheric composition of individual stars. Upon undertaking such a task, observations indicate a strong negative correlation between a star's heavy element content (metallicity) and its age (red shift): more recently formed stars tend to have higher metallicity.
Big bang nucleosynthesis tells us that the early universe consisted of only the light elements, and so one expects the first stars to be composed of hydrogen, helium, and lithium, the three lightest elements. Stellar structure and the Hertzsprung–Russell diagram indicate that the lifetime of a star depends greatly on its initial mass, so that massive stars are very short-lived, and less massive stars are longer-lived. As a star dies, B2FH argues that it will enrich the interstellar medium with 'heavy elements' (in this case all elements heavier than lithium, the third element), from which new stars are formed. This account is consistent with the observed negative correlation between stellar metallicity and red shift.
The theory of stellar nucleosynthesis advocated by B2FH also detailed the nuclear physics and astrophysics involved. By carefully scrutinizing the table of nuclides, the authors were able to predict the existence of different stellar environments which could produce the observed isotopic abundances, and the nuclear processes which must occur in these stars. In this paper, among other things, the authors predicted the existence of the p-process, r-process, and s-process to account for many of the elements heavier than iron, and these ideas have since come to bear much fruit.
Writing of the paper
Margaret and Geoffrey Burbidge wrote the first draft of the paper, incorporating extensive observations and experimental data to support the theory. Both Hoyle and Fowler worked extensively on the early draft. Geoffrey Burbidge says that it is a misconception some have had that Fowler was the leader of the group. "There was no leader in the group," he wrote in 2008, "We all made substantial contributions."
Because this work firmly established the field of nuclear astrophysics, William Fowler was awarded half of the 1983 Nobel Prize in Physics for his contributions; some believe that Fred Hoyle also deserved similar recognition for his scholarship on this topic, and contend that his unorthodox views concerning the big bang played a role in his lack of a Nobel Prize.
Geoffrey Burbidge wrote in 2008, "Hoyle should have been awarded a Nobel Prize for this and other work. On the basis of my private correspondence, I believe that a major reason for his exclusion was that W.A. Fowler was believed to be the leader of the group." Burbidge states that this perception is not true and also points to Hoyle's earlier papers from 1946 as indicators of Hoyle's authorship of the theory of stellar nucleosynthesis. and 1954 Burbidge said that "Hoyle's work has been undercited in part because it was published in an astrophysical journal, and a new one at that (the very first volume, in fact), whereas B2FH was published in a well-established physics journal, Reviews of Modern Physics. When B2FH was first written, preprints were widely distributed to the nuclear physics community. Willy Fowler was very well known as a leader in that community, and the California Institute of Technology already had a news bureau that knew how to spread the word.
- E. M. Burbidge, G. R. Burbidge, W. A. Fowler, and F. Hoyle (1957). "Synthesis of the Elements in Stars". Reviews of Modern Physics 29 (4): 547. Bibcode:1957RvMP...29..547B. doi:10.1103/RevModPhys.29.547.
- H. A. Bethe and C. L. Critchfield (1938). "The Formation of Deuterons by Proton Combination". Physical Review 54 (4): 248. Bibcode:1938PhRv...54..248B. doi:10.1103/PhysRev.54.248.
- C. F. von Weizsäcker (1938). "Über Elementumwandlungen in Innern der Sterne II". Physikalische Zeitschrift 39: 633.
- H. A. Bethe (1939). "Energy Production in Stars". Physical Review 55 (5): 434. Bibcode:1939PhRv...55..434B. doi:10.1103/PhysRev.55.434.
- Wallerstein, George, et al. (October 1997). "Synthesis of the elements in stars: forty years of progress". Reviews of Modern Physics 69 (4): 995–1084. Bibcode:1997RvMP...69..995W. doi:10.1103/RevModPhys.69.995. Retrieved 16 November 2011. Page 998.
- G. Burbidge (2008). "Hoyle's Role in B2FH". Science 319 (5869): 1484. doi:10.1126/science.319.5869.1484b. PMID 18339922.
- McKie, Robin (2 October 2010). "Fred Hoyle: the scientist whose rudeness cost him a Nobel prize". The Guardian. Retrieved 3 March 2013.
- F. Hoyle (1946). "The Synthesis of the Elements from Hydrogen". Monthly Notices of the Royal Astronomical Society 106: 343. Bibcode:1946MNRAS.106..343H.
- F. Hoyle (1954). "On Nuclear Reactions Occuring in Very Hot Stars. I. The Synthesis of Elements from Carbon to Nickel". Astrophysical Journal Supplement 1: 121. Bibcode:1954ApJS....1..121H. doi:10.1086/190005.
- "Nuclear Astrophysics: 1957–2007 – Beyond the first 50 years". California Institute of Technology. July 2007. Retrieved 2011-04-14.