B2FH paper

The B²FH paper, named after the initials of the authors of the paper, Margaret Burbidge, Geoffrey Burbidge, William Fowler, and Fred Hoyle, is a landmark paper of stellar physics published in Reviews of Modern Physics in 1957.^[1] 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 it 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. Together, Hans Bethe and Charles L. Critchfield had derived the Proton proton chain (pp-chain) in 1938,^[2] and Carl von Weizsäcker^[3] and Hans Bethe^[4] 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.

At the time, stellar fusion theories did not show how to create any elements heavier than helium, however, and Gamow advocated the theory that all elements were residual from the big bang, allowing for slight changes in the ratios of hydrogen and helium.

The four collaborators who authored B²FH gave a different account for the origin of heavy elements, however, suggesting that all atomic nuclei heavier than lithium up to uranium must have been synthesized in stars rather than 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 the authors of B²FH argued that a majority of all elements except for hydrogen must come from stars, their ideas are called the theory of stellar nucleosynthesis.^[5] 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) and, that 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 length of 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. B²FH argues that as a star dies, it will enrich the interstellar medium with 'heavy elements' (in this case all elements heavier than lithium, the third element), from which newer 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 the authors of B²FH also detailed the nuclear physics and astrophysics involved. By carefully scrutinizing the table of nuclides, they were able to predict the existence of different stellar environments that could produce the observed isotopic abundances, and the nuclear processes that 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. These ideas have since come to bear much fruit.

Writing of the paper

Margaret Burbidge 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 has asserted that it is a misconception some have had, to presume that Fowler was the leader of the group. "There was no leader in the group," he wrote in 2008, "we all made substantial contributions."^[6]

Recognition

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 they contend that his unorthodox views concerning the big bang played a role in his not being awarded a Nobel Prize.^[7]

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."^[6] Burbidge stated that this perception is not true and also points to Hoyle's earlier papers from 1946 as indicators of Hoyle's role in the authorship of the theory of stellar nucleosynthesis.^[8] and 1954^[9] Burbidge said that "Hoyle's work has been undercited in part because it was published in an astrophysical journal,^[9] 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."

In 2007 a conference was held in Pasadena, California to commemorate the 50th anniversary of the publication of this influential paper.^[10]

See also

• Alpher–Bethe–Gamow paper

Further reading

• Burbidge, E. Margaret; Burbidge, G. R.; Fowler, William A.; Hoyle, F. (1957). "Synthesis of the Elements in Stars". Reviews of Modern Physics. 29 (4): 547–650. Bibcode:1957RvMP...29..547B. doi:10.1103/RevModPhys.29.547 . 

References