B2FH paper. Synthesis of the Elements in Stars
The authors of the B2FH paper
The B2FH paper (pronounced "B squared FH"), named after the initials of the authors of the paper, Margaret Burbidge (1919–2020), Geoffrey Burbidge (1925–2010), William A. Fowler (1911–1995), and Fred Hoyle (1915–2001), was a landmark paper on the origin of the chemical elements. It was written at Caltech in 1956, primarily by the Burbidges and Fowler, and pubnished in Reviews of Modern Physics on October 1, 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 reviewed stellar nucleosynthesis theory and supported it with astronomical and laboratory data. Elements, the authors argued, are slowly built up by fusion in the cores of stars, so that hydrogen fuses to helium, then to carbon, oxygen, silicon, all of the elements up to iron. The remaining elements are byproducts of the energy released in supernova explosions, which not only produce the rest of the elements up to uranium, but explode them out into the interstellar medium, where they become the building blocks for future stars. The B2FH paper was over 100 pages long, with lots of supporting data to show that chemical abundances in the universe have changed over time. It identified nucleosynthesis processes that are responsible for producing the elements heavier than iron and explained their relative abundances. The paper became highly influential in both astronomy and nuclear physics.
Beginning with a paper in 1946, and expanded upon in 1954, Fred Hoyle proposed that all atomic nuclei heavier than lithium were synthesized in stars. Some light nuclei (hydrogen, helium and a small amount of lithium) were not produced in stars, which became the now-accepted theory of Big Bang nucleosynthesis of H, He and Li. The B2FH paper was ostensibly a review article summarising recent advances in the theory of stellar nucleosynthesis. However, it went beyond simply reviewing Hoyle's work, by incorporating observational measurements of elemental abundances published by the Burbidges, and Fowler's laboratory experiments on nuclear reactions. The result was a synthesis of theory and observation, which provided convincing evidence for Hoyle's hypothesis. The theory predicted that the abundances of the elements would evolve over cosmological time, an idea which is testable by astronomical spectroscopy. Each element has a characteristic set of spectral lines, so stellar spectroscopy can be used to infer the atmospheric composition of individual stars. Observations indicate a strong negative correlation between a star's initial heavy element content (known as the metallicity) and its age. More recently formed stars tend to have higher metallicity. The early Universe consisted of only the light elements formed during Big Bang nucleosynthesis. Stellar structure and the Hertzsprung–Russell diagram indicate that the length of the lifetime of a star depends greatly on its initial mass, with the most massive stars being very short-lived, and less massive stars are longer-lived. The B2FH paper argued that when a star dies, it will enrich the interstellar medium with 'heavy elements' (in this case all elements heavier than lithium), from which newer stars are formed. The paper described key aspects of the nuclear physics and astrophysics involved in how stars produce these heavy elements.
By scrutinizing the table of nuclides, the authors identified different stellar environments that could produce the observed isotopic abundance patterns and the nuclear processes that must be responsible for them. The authors invoke nuclear physics processes, now known as the p-process, r-process, and s-process, to account for the elements heavier than iron. The abundances of these heavy elements and their isotopes are roughly 100,000 times less than those of the major elements, which supported Hoyle's 1954 hypothesis of nuclear fusion within the burning shells of massive stars. B2FH comprehensively outlined and analyzed the nucleosynthesis of the elements heavier than iron by the capture within stars of free neutrons. It advanced much less the understanding of the synthesis of the very abundant elements from silicon to nickel. The paper did not include the carbon-burning process, the oxygen-burning process and the silicon-burning process, each of which contribute to the elements from magnesium to nickel. Hoyle had already suggested that supernova nucleosynthesis could be responsible for these in his 1954 paper.
The B2FH paper is one of the milestone publications in 20th-century science. William Fowler was awarded the 1983 Nobel Prize in Physics for his theoretical and experimental studies of the nuclear reactions of importance in the formation of the chemical elements in the universe, possibly for his contribution to B2FH. Why Hoyle was not included in the award is not known to this day.
The paper reviewed stellar nucleosynthesis theory and supported it with astronomical and laboratory data. Elements, the authors argued, are slowly built up by fusion in the cores of stars, so that hydrogen fuses to helium, then to carbon, oxygen, silicon, all of the elements up to iron. The remaining elements are byproducts of the energy released in supernova explosions, which not only produce the rest of the elements up to uranium, but explode them out into the interstellar medium, where they become the building blocks for future stars. The B2FH paper was over 100 pages long, with lots of supporting data to show that chemical abundances in the universe have changed over time. It identified nucleosynthesis processes that are responsible for producing the elements heavier than iron and explained their relative abundances. The paper became highly influential in both astronomy and nuclear physics.
Beginning with a paper in 1946, and expanded upon in 1954, Fred Hoyle proposed that all atomic nuclei heavier than lithium were synthesized in stars. Some light nuclei (hydrogen, helium and a small amount of lithium) were not produced in stars, which became the now-accepted theory of Big Bang nucleosynthesis of H, He and Li. The B2FH paper was ostensibly a review article summarising recent advances in the theory of stellar nucleosynthesis. However, it went beyond simply reviewing Hoyle's work, by incorporating observational measurements of elemental abundances published by the Burbidges, and Fowler's laboratory experiments on nuclear reactions. The result was a synthesis of theory and observation, which provided convincing evidence for Hoyle's hypothesis. The theory predicted that the abundances of the elements would evolve over cosmological time, an idea which is testable by astronomical spectroscopy. Each element has a characteristic set of spectral lines, so stellar spectroscopy can be used to infer the atmospheric composition of individual stars. Observations indicate a strong negative correlation between a star's initial heavy element content (known as the metallicity) and its age. More recently formed stars tend to have higher metallicity. The early Universe consisted of only the light elements formed during Big Bang nucleosynthesis. Stellar structure and the Hertzsprung–Russell diagram indicate that the length of the lifetime of a star depends greatly on its initial mass, with the most massive stars being very short-lived, and less massive stars are longer-lived. The B2FH paper argued that when a star dies, it will enrich the interstellar medium with 'heavy elements' (in this case all elements heavier than lithium), from which newer stars are formed. The paper described key aspects of the nuclear physics and astrophysics involved in how stars produce these heavy elements.
By scrutinizing the table of nuclides, the authors identified different stellar environments that could produce the observed isotopic abundance patterns and the nuclear processes that must be responsible for them. The authors invoke nuclear physics processes, now known as the p-process, r-process, and s-process, to account for the elements heavier than iron. The abundances of these heavy elements and their isotopes are roughly 100,000 times less than those of the major elements, which supported Hoyle's 1954 hypothesis of nuclear fusion within the burning shells of massive stars. B2FH comprehensively outlined and analyzed the nucleosynthesis of the elements heavier than iron by the capture within stars of free neutrons. It advanced much less the understanding of the synthesis of the very abundant elements from silicon to nickel. The paper did not include the carbon-burning process, the oxygen-burning process and the silicon-burning process, each of which contribute to the elements from magnesium to nickel. Hoyle had already suggested that supernova nucleosynthesis could be responsible for these in his 1954 paper.
The B2FH paper is one of the milestone publications in 20th-century science. William Fowler was awarded the 1983 Nobel Prize in Physics for his theoretical and experimental studies of the nuclear reactions of importance in the formation of the chemical elements in the universe, possibly for his contribution to B2FH. Why Hoyle was not included in the award is not known to this day.
The first page of the B2FH paper
References:
E. Margaret Burbidge, G. R. Burbidge, William A. Fowler, and F. Hoyle (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 [full paper in pdf]
© 2025, Andrew Mirecki
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