B2FH paper

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The B2FH paper [1] was a landmark scientific paper on the origin of the chemical elements. The paper's title is Synthesis of the Elements in Stars, but it became known as B2FH from the initials of its authors: Margaret Burbidge, Geoffrey Burbidge, William A. Fowler, and Fred Hoyle. It was written from 1955 to 1956 at the University of Cambridge and Caltech, then published in Reviews of Modern Physics in 1957.

Contents

The B2FH paper reviewed stellar nucleosynthesis theory and supported it with astronomical and laboratory data. 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.

Nucleosynthesis prior to 1957

Prior to the publication of the B2FH paper, George Gamow advocated a theory of the Universe in which almost all chemical elements, or equivalently atomic nuclei, were synthesized during the Big Bang. Gamow's theory (which differs from present-day Big Bang nucleosynthesis theory) would imply that the abundance of the chemical elements would remain mostly static over time. Hans Bethe and Charles L. Critchfield had shown that the conversion of hydrogen into helium by nuclear fusion could provide the energy required to power stars, by deriving the proton-proton chain (pp-chain) in 1938. [2] Carl von Weizsäcker [3] and Hans Bethe [4] had independently derived the CNO cycle in 1938 and 1939, respectively. Thus, it was known by Gamow and others that the abundances of hydrogen and helium were not perfectly static. According to their view, fusion in stars would produce small amounts of helium, adding only slightly to its abundance from the Big Bang. This stellar nuclear power did not require substantial stellar nucleosynthesis. The elements from carbon upward remained a mystery.

Fred Hoyle offered a hypothesis for the origin of heavy elements. Beginning with a paper in 1946, and expanded upon in 1954, [5] Hoyle proposed that all atomic nuclei heavier than lithium were synthesized in stars. Both theories agreed that 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.

Physics in the paper

The B2FH paper was ostensibly a review article summarising recent advances in the theory of stellar nucleosynthesis. [6] 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 B2FH 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. [5]

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. [5] Donald D. Clayton has attributed the lower number of citations to Hoyle's 1954 paper compared to B2FH as a combination of factors: the difficulty of digesting Hoyle's 1954 paper even for his B2FH coauthors, and among astronomers generally; to Hoyle's having described its key equation only in words [7] rather than writing it prominently in his paper; and to Hoyle's incomplete review of the B2FH draft. [8]

Writing of the paper

The Caltech nuclear physicist William Alfred Fowler used his sabbatical leave to visit Hoyle in Cambridge from 1954 to 1955. The pair invited Margaret Burbidge and Geoffrey Burbidge to join them in Cambridge, as the couple had recently published extensive work on stellar abundances that would be required to test Hoyle's hypothesis. The quartet collaborated on several projects whilst in Cambridge; Fowler and Hoyle began work on a review that would become B2FH. Fowler returned to Caltech with the work far from complete, and encouraged the Burbidges to join him in California. Both of the Burbidges had temporary positions created for them in 1956 at Caltech by Fowler for this purpose.[ citation needed ] The first complete draft was completed by the Burbidges in 1956 at Caltech, after adding extensive astronomical observations and experimental data to support the theory. Margaret Burbidge, the paper's first author, completed much of the work whilst pregnant. [9] The final paper is 104 pages long, with 34 plots, 4 photographic plates, and 22 tables; despite this length, it does not have an abstract. [1]

Some have presumed that Fowler was the leader of the group because the writing and submission for publication were done at Caltech in 1956, but Geoffrey Burbidge has stated that this is a misconception. Fowler, though an accomplished nuclear physicist, was still learning Hoyle's theory in 1955 and later stated that Hoyle was the intellectual leader. [10] The Burbidges also learnt Hoyle's theory during 1954–55 in Cambridge. "There was no leader in the group," G. Burbidge wrote in 2008, "we all made substantial contributions". [11]

Recognition

B2FH drew scientific attention to the field of nuclear astrophysics. By reviewing the theory of stellar nucleosynthesis and supporting it with observational evidence, B2FH firmly established the theory among astronomers.

Fowler was awarded half of the 1983 Nobel Prize in Physics, arguably for his contributions to B2FH. The Nobel committee stated: "Together with a number of co-workers, [Fowler] developed, during the 1950s, a complete theory of the formation of the chemical elements in the universe." [12] Fowler's contributions to B2FH included the nuclear physics of the s-process and the r-process.

Some have argued that Fred Hoyle deserved similar recognition for theoretical work on the topic, and contend that his unorthodox views concerning the Big Bang stopped him being awarded a share of the Nobel Prize. Geoffrey Burbidge, for example, argued in 2008 that "Hoyle should have been awarded a Nobel Prize for this and other work". He also speculated that the reason why Hoyle ended up empty-handed was that "Fowler was believed to be the leader of the group." [11] Burbidge insisted that this perception was false and pointed to Hoyle's earlier foundational papers from 1946 [13] and 1954. [5]

Fowler, in his own Nobel lecture, wrote about Hoyle: "Fred Hoyle was the second great influence in my life. The grand concept of nucleosynthesis in stars was first definitely established by Hoyle in 1946." [14]

Hoyle's biographer Mitton has speculated that Hoyle was left out by the Nobel committee because he had earlier spoken out against the injustice the Nobel committee overlooking Jocelyn Bell Burnell for the 1974 prize. [15]

In 2007 a conference was held at Caltech in Pasadena, California to commemorate the 50th anniversary of the publication of B2FH, [16] where Geoffrey Burbidge presented remarks on the writing of B2FH.

See also

Further reading

Related Research Articles

<span class="mw-page-title-main">Fred Hoyle</span> English astronomer (1915–2001)

Sir Fred Hoyle (24 June 1915 – 20 August 2001) was an English astronomer who formulated the theory of stellar nucleosynthesis and was one of the authors of the influential B2FH paper. He also held controversial stances on other scientific matters—in particular his rejection of the "Big Bang" theory (a term coined by him on BBC Radio) in favor of the "steady-state model", and his promotion of panspermia as the origin of life on Earth. He spent most of his working life at the Institute of Astronomy at Cambridge and served as its director for six years.

In physical cosmology, Big Bang nucleosynthesis is the production of nuclei other than those of the lightest isotope of hydrogen during the early phases of the universe. This type of nucleosynthesis is thought by most cosmologists to have occurred from 10 seconds to 20 minutes after the Big Bang. It is thought to be responsible for the formation of most of the universe's helium, along with small fractions of the hydrogen isotope deuterium, the helium isotope helium-3 (3He), and a very small fraction of the lithium isotope lithium-7 (7Li). In addition to these stable nuclei, two unstable or radioactive isotopes were produced: the heavy hydrogen isotope tritium and the beryllium isotope beryllium-7 (7Be). These unstable isotopes later decayed into 3He and 7Li, respectively, as above.

Nucleosynthesis is the process that creates new atomic nuclei from pre-existing nucleons and nuclei. According to current theories, the first nuclei were formed a few minutes after the Big Bang, through nuclear reactions in a process called Big Bang nucleosynthesis. After about 20 minutes, the universe had expanded and cooled to a point at which these high-energy collisions among nucleons ended, so only the fastest and simplest reactions occurred, leaving our universe containing hydrogen and helium. The rest is traces of other elements such as lithium and the hydrogen isotope deuterium. Nucleosynthesis in stars and their explosions later produced the variety of elements and isotopes that we have today, in a process called cosmic chemical evolution. The amounts of total mass in elements heavier than hydrogen and helium remains small, so that the universe still has approximately the same composition.

<span class="mw-page-title-main">Triple-alpha process</span> Nuclear fusion reaction chain converting helium to carbon

The triple-alpha process is a set of nuclear fusion reactions by which three helium-4 nuclei are transformed into carbon.

<span class="mw-page-title-main">Stellar nucleosynthesis</span> Creation of chemical elements within stars

Stellar nucleosynthesis is the creation (nucleosynthesis) of chemical elements by nuclear fusion reactions within stars. Stellar nucleosynthesis has occurred since the original creation of hydrogen, helium and lithium during the Big Bang. As a predictive theory, it yields accurate estimates of the observed abundances of the elements. It explains why the observed abundances of elements change over time and why some elements and their isotopes are much more abundant than others. The theory was initially proposed by Fred Hoyle in 1946, who later refined it in 1954. Further advances were made, especially to nucleosynthesis by neutron capture of the elements heavier than iron, by Margaret and Geoffrey Burbidge, William Alfred Fowler and Fred Hoyle in their famous 1957 B2FH paper, which became one of the most heavily cited papers in astrophysics history.

<i>r</i>-process Nucleosynthesis pathway

In nuclear astrophysics, the rapid neutron-capture process, also known as the r-process, is a set of nuclear reactions that is responsible for the creation of approximately half of the atomic nuclei heavier than iron, the "heavy elements", with the other half produced by the p-process and s-process. The r-process usually synthesizes the most neutron-rich stable isotopes of each heavy element. The r-process can typically synthesize the heaviest four isotopes of every heavy element, and the two heaviest isotopes, which are referred to as r-only nuclei, can be created via the r-process only. Abundance peaks for the r-process occur near mass numbers A = 82, A = 130 and A = 196.

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<span class="mw-page-title-main">Margaret Burbidge</span> British-born American astrophysicist

Eleanor Margaret Burbidge, FRS (née Peachey; 12 August 1919 – 5 April 2020) was a British-American observational astronomer and astrophysicist. In the 1950s, she was one of the founders of stellar nucleosynthesis and was first author of the influential B2FH paper. During the 1960s and 1970s she worked on galaxy rotation curves and quasars, discovering the most distant astronomical object then known. In the 1980s and 1990s she helped develop and utilise the Faint Object Spectrograph on the Hubble Space Telescope. Burbidge was also well known for her work opposing discrimination against women in astronomy.

<span class="mw-page-title-main">William Alfred Fowler</span> American nuclear physicist (1911–1995)

William Alfred Fowler (August 9, 1911 – March 14, 1995) was an American nuclear physicist, later astrophysicist, who, with Subrahmanyan Chandrasekhar, was awarded the 1983 Nobel Prize in Physics. He is known for his theoretical and experimental research into nuclear reactions within stars and the energy elements produced in the process and was one of the authors of the influential B2FH paper.

<span class="mw-page-title-main">Geoffrey Burbidge</span> British astronomer

Geoffrey Ronald Burbidge (24 September 1925 – 26 January 2010) was an English astronomy professor and theoretical astrophysicist, most recently at the University of California, San Diego. He was married to astrophysicist Margaret Burbidge and was the second author of the influential B2FH paper which she led.

<span class="mw-page-title-main">Ralph Asher Alpher</span> American cosmologist

Ralph Asher Alpher was an American cosmologist, who carried out pioneering work in the early 1950s on the Big Bang model, including Big Bang nucleosynthesis and predictions of the cosmic microwave background radiation.

Supernova nucleosynthesis is the nucleosynthesis of chemical elements in supernova explosions.

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Alastair G. W. Cameron was an American–Canadian astrophysicist and space scientist who was an eminent staff member of the Astronomy department of Harvard University. He was one of the founders of the field of nuclear astrophysics, advanced the theory that the Moon was created by the giant impact of a Mars-sized object with the early Earth, and was an early adopter of computer technology in astrophysics.

Neutron capture nucleosynthesis describes two nucleosynthesis pathways: the r-process and the s-process, for rapid and slow neutron captures, respectively. R-process describes neutron capture in a region of high neutron flux, such as during supernova nucleosynthesis after core-collapse, and yields neutron-rich nuclides. S-process describes neutron capture that is slow relative to the rate of beta decay, as for stellar nucleosynthesis in some stars, and yields nuclei with stable nuclear shells. Each process is responsible for roughly half of the observed abundances of elements heavier than iron. The importance of neutron capture to the observed abundance of the chemical elements was first described in 1957 in the B2FH paper.

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<span class="mw-page-title-main">Donald D. Clayton</span> American astrophysicist

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References

  1. 1 2 E. M. Burbidge; G. R. Burbidge; W. A. Fowler; F. Hoyle (1957). "Synthesis of the Elements in Stars" (PDF). Reviews of Modern Physics . 29 (4): 547. Bibcode:1957RvMP...29..547B. doi: 10.1103/RevModPhys.29.547 .
  2. ↑ H. A. Bethe; 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.
  3. ↑ C. F. von Weizsäcker (1938). "Über Elementumwandlungen in Innern der Sterne II". Physikalische Zeitschrift . 39: 633.
  4. ↑ H. A. Bethe (1939). "Energy Production in Stars". Physical Review . 55 (5): 434. Bibcode:1939PhRv...55..434B. doi: 10.1103/PhysRev.55.434 .
  5. 1 2 3 4 F. Hoyle (1954). "On Nuclear Reactions Occurring 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 .
  6. ↑ G. Wallerstein; et al. (1997). "Synthesis of the elements in stars: forty years of progress" (PDF). Reviews of Modern Physics . 69 (4): 995–1084. Bibcode:1997RvMP...69..995W. doi:10.1103/RevModPhys.69.995. hdl: 2152/61093 . Archived from the original (PDF) on 9 September 2011.
  7. ↑ Donald D. Clayton (2007). "Hoyle's Equation". Science . 318 (5858): 1876–1877. doi:10.1126/science.1151167. PMID   18096793. S2CID   118423007.
  8. ↑ See footnote 1 in Donald D. Clayton (2008). "Fred Hoyle, primary nucleosynthesis and radioactivity". New Astronomy Reviews . 32 (7–10): 360–363. Bibcode:2008NewAR..52..360C. doi:10.1016/j.newar.2008.05.007.
  9. ↑ Skuse, Ben (6 April 2020). "Celebrating Astronomer Margaret Burbidge, 1919–2020". Sky & Telescope . Retrieved 6 April 2020.
  10. ↑ "William A. Fowler – Nobel Lecture: Experimental and Theoretical Nuclear Astrophysics; the Quest for the Origin of the Elements". Nobelprize.org. Nobel Media AB 2014. Web. 29 Mar 2018. http://www.nobelprize.org/nobel_prizes/physics/laureates/1983/fowler-lecture.html (see Biographical)
  11. 1 2 G. Burbidge (2008). "Hoyle's Role in B2FH". Science . 319 (5869): 1484. doi:10.1126/science.319.5869.1484b. PMID   18339922. S2CID   206579529.
  12. ↑ "The Nobel Prize in Physics 1983". NobelPrize.org. Retrieved 2023-12-06.
  13. ↑ F. Hoyle (1946). "The Synthesis of the Elements from Hydrogen" (PDF). Monthly Notices of the Royal Astronomical Society . 106 (5): 343. Bibcode: 1946MNRAS.106..343H . doi: 10.1093/mnras/106.5.343 .
  14. ↑ "The Nobel Prize in Physics 1983". NobelPrize.org. Retrieved 2023-12-07.
  15. ↑ R. McKie (2 October 2010). "Fred Hoyle: the scientist whose rudeness cost him a Nobel prize". The Guardian . Retrieved 3 March 2013.
  16. ↑ "Nuclear Astrophysics: 1957–2007 – Beyond the first 50 years". California Institute of Technology. July 2007. Archived from the original on 2011-05-07. Retrieved 2011-04-14.
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