B²FH
Encyclopedia
The B2FH paper, named after the initials of 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 so famous that it is typically 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
.
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 through uranium
) must have been synthesized in star
s 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
.
. An often quoted statement of Carl Sagan
, "We are all star stuff," is simply his paraphrase of this review paper's thesis. The key difference between this theory of stellar nucleosynthesis and all previous accounts for the origin of the elements is that B2FH predicts 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. However, upon undertaking such a task, observations indicate a strong negative correlation
between a star's heavy element content (metallicity
) and its age (red shift
): younger 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.
However, the theory of stellar nucleosynthesis advocated by B2FH would not be very convincing if it could not also detail 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.
and Geoffrey Burbidge
wrote the first draft of the paper, deliberately 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."
, 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 and 1954 as indicators of Hoyle's authorship of the theory of stellar nucleosynthesis
. Burbidge explains, "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.
In 2007 a conference was held in Pasadena, California
to commemorate the 50th anniversary of the publication of this influential paper.
Margaret Burbidge
Eleanor Margaret Burbidge, née Peachey, FRS is a British-born American astrophysicist, noted for original research and holding many administrative posts, including director of the Royal Greenwich Observatory....
, Geoffrey Burbidge
Geoffrey Burbidge
Geoffrey Ronald Burbidge FRS was an English astronomy professor, most recently at the University of California, San Diego. He was married to astrophysicist Dr. Margaret Burbidge.-Education:...
, William Fowler
William Alfred Fowler
William Alfred "Willy" Fowler was an American astrophysicist and winner of the Nobel Prize for Physics in 1983. He should not be confused with the British astronomer Alfred Fowler....
and Fred Hoyle
Fred Hoyle
Sir Fred Hoyle FRS was an English astronomer and mathematician noted primarily for his contribution to the theory of stellar nucleosynthesis and his often controversial stance on other cosmological and scientific matters—in particular his rejection of the "Big Bang" theory, a term originally...
, is a landmark paper of stellar physics
Stellar physics
Stellar physics, is a term coined for the research concerning the formation, evolution, interior and the atmospheres of stars. The understanding of the birth and death of stars requires the application of almost all branches of modern physics...
published in Reviews of Modern Physics
Reviews of Modern Physics
The Reviews of Modern Physics is a journal of the American Physical Society. The journal started in paper form. All volumes are also online by subscription.Issue 1, Volume 1 consisted of the review by...
in 1957. The formal title of the paper is Synthesis of the Elements in Stars, but the article is so famous that it is typically 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
Nucleosynthesis
Nucleosynthesis is the process of creating new atomic nuclei from pre-existing nucleons . It is thought that the primordial nucleons themselves were formed from the quark–gluon plasma from the Big Bang as it cooled below two trillion degrees...
and their relative abundance
Abundance of the chemical elements
The abundance of a chemical element measures how relatively common the element is, or how much of the element is present in a given environment by comparison to all other elements...
, and is credited with originating what is now the theory of stellar nucleosynthesis
Stellar nucleosynthesis
Stellar nucleosynthesis is the collective term for the nuclear reactions taking place in stars to build the nuclei of the elements heavier than hydrogen. Some small quantity of these reactions also occur on the stellar surface under various circumstances...
.
Physics in 1957
At the time of the publication of the B2FH paper, George GamowGeorge Gamow
George Gamow , born Georgiy Antonovich Gamov , was a Russian-born theoretical physicist and cosmologist. He discovered alpha decay via quantum tunneling and worked on radioactive decay of the atomic nucleus, star formation, stellar nucleosynthesis, Big Bang nucleosynthesis, cosmic microwave...
advocated a theory of the universe according to which virtually all elements
Chemical element
A chemical element is a pure chemical substance consisting of one type of atom distinguished by its atomic number, which is the number of protons in its nucleus. Familiar examples of elements include carbon, oxygen, aluminum, iron, copper, gold, mercury, and lead.As of November 2011, 118 elements...
, or atomic nuclei
Atomic nucleus
The nucleus is the very dense region consisting of protons and neutrons at the center of an atom. It was discovered in 1911, as a result of Ernest Rutherford's interpretation of the famous 1909 Rutherford experiment performed by Hans Geiger and Ernest Marsden, under the direction of Rutherford. The...
, were synthesized during the big bang
Big Bang
The Big Bang theory is the prevailing cosmological model that explains the early development of the Universe. According to the Big Bang theory, the Universe was once in an extremely hot and dense state which expanded rapidly. This rapid expansion caused the young Universe to cool and resulted in...
. The implications of Gamow's nucleosynthesis theory (not to be confused with present-day nucleosynthesis
Nucleosynthesis
Nucleosynthesis is the process of creating new atomic nuclei from pre-existing nucleons . It is thought that the primordial nucleons themselves were formed from the quark–gluon plasma from the Big Bang as it cooled below two trillion degrees...
theory) is that nuclear abundances
Abundance of the chemical elements
The abundance of a chemical element measures how relatively common the element is, or how much of the element is present in a given environment by comparison to all other elements...
in the universe are largely static. Hans Bethe
Hans Bethe
Hans Albrecht Bethe was a German-American nuclear physicist, and Nobel laureate in physics for his work on the theory of stellar nucleosynthesis. A versatile theoretical physicist, Bethe also made important contributions to quantum electrodynamics, nuclear physics, solid-state physics and...
and Charles L. Critchfield had together derived the pp-chain in 1938, and Carl von Weizsäcker
Carl Friedrich von Weizsäcker
Carl Friedrich Freiherr von Weizsäcker was a German physicist and philosopher. He was the longest-living member of the research team which performed nuclear research in Germany during the Second World War, under Werner Heisenberg's leadership...
and Hans Bethe had independently derived the CNO cycle
CNO cycle
The CNO cycle is one of two sets of fusion reactions by which stars convert hydrogen to helium, the other being the proton–proton chain. Unlike the proton–proton chain reaction, the CNO cycle is a catalytic cycle. Theoretical models show that the CNO cycle is the dominant source of energy in stars...
in 1938 and 1939, respectively, to show that the conversion of hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
to helium
Helium
Helium is the chemical element with atomic number 2 and an atomic weight of 4.002602, which is represented by the symbol He. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas that heads the noble gas group in the periodic table...
by nuclear fusion
Nuclear fusion
Nuclear fusion is the process by which two or more atomic nuclei join together, or "fuse", to form a single heavier nucleus. This is usually accompanied by the release or absorption of large quantities of energy...
could account for stellar energy production. Thus, it was known by Gamow and others in 1957 that the abundances
Abundance of the chemical elements
The abundance of a chemical element measures how relatively common the element is, or how much of the element is present in a given environment by comparison to all other elements...
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
Lithium
Lithium is a soft, silver-white metal that belongs to the alkali metal group of chemical elements. It is represented by the symbol Li, and it has the atomic number 3. Under standard conditions it is the lightest metal and the least dense solid element. Like all alkali metals, lithium is highly...
(up through uranium
Uranium
Uranium is a silvery-white metallic chemical element in the actinide series of the periodic table, with atomic number 92. It is assigned the chemical symbol U. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons...
) must have been synthesized in star
Star
A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...
s 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
Big Bang nucleosynthesis
In physical cosmology, Big Bang nucleosynthesis refers to the production of nuclei other than those of H-1 during the early phases of the universe...
.
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 nucleosynthesisStellar nucleosynthesis
Stellar nucleosynthesis is the collective term for the nuclear reactions taking place in stars to build the nuclei of the elements heavier than hydrogen. Some small quantity of these reactions also occur on the stellar surface under various circumstances...
. An often quoted statement of Carl Sagan
Carl Sagan
Carl Edward Sagan was an American astronomer, astrophysicist, cosmologist, author, science popularizer and science communicator in astronomy and natural sciences. He published more than 600 scientific papers and articles and was author, co-author or editor of more than 20 books...
, "We are all star stuff," is simply his paraphrase of this review paper's thesis. The key difference between this theory of stellar nucleosynthesis and all previous accounts for the origin of the elements is that B2FH predicts chemical evolution
Chemical evolution
Chemical evolution may refer to:*Nucleosynthesis, the creation of chemical elements in the universe either through the Big Bang, or supernovae*Abiogenesis, the transition from nonliving elements to living systems...
of the universe, which is testable by looking at stellar spectral lines. Quantum mechanics
Quantum mechanics
Quantum mechanics, also known as quantum physics or quantum theory, is a branch of physics providing a mathematical description of much of the dual particle-like and wave-like behavior and interactions of energy and matter. It departs from classical mechanics primarily at the atomic and subatomic...
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. However, upon undertaking such a task, observations indicate a strong negative correlation
Negative relationship
In statistics, a relationship between two variables is negative if the slope in a corresponding graph is negative, or—what is in some contexts equivalent—if the correlation between them is negative...
between a star's heavy element content (metallicity
Metallicity
In astronomy and physical cosmology, the metallicity of an object is the proportion of its matter made up of chemical elements other than hydrogen and helium...
) and its age (red shift
Red shift
-Science:* Redshift, the increase of wavelength of detected electromagnetic radiation with respect to the original wavelength of the emission* Red shift, an informal term for a bathochromic shift...
): younger stars tend to have higher metallicity.
Big bang nucleosynthesis
Big Bang nucleosynthesis
In physical cosmology, Big Bang nucleosynthesis refers to the production of nuclei other than those of H-1 during the early phases of the universe...
tells us that the early universe consisted of only the light elements, and so one expects the first stars to be composed of hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
, helium
Helium
Helium is the chemical element with atomic number 2 and an atomic weight of 4.002602, which is represented by the symbol He. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas that heads the noble gas group in the periodic table...
, and lithium
Lithium
Lithium is a soft, silver-white metal that belongs to the alkali metal group of chemical elements. It is represented by the symbol Li, and it has the atomic number 3. Under standard conditions it is the lightest metal and the least dense solid element. Like all alkali metals, lithium is highly...
, the three lightest elements. Stellar structure
Stellar structure
Stars of different mass and age have varying internal structures. Stellar structure models describe the internal structure of a star in detail and make detailed predictions about the luminosity, the color and the future evolution of the star....
and the Hertzsprung–Russell diagram
Hertzsprung–Russell diagram
The Hertzsprung–Russell diagram is a scatter graph of stars showing the relationship between the stars' absolute magnitudes or luminosities versus their spectral types or classifications and effective temperatures. Hertzsprung–Russell diagrams are not pictures or maps of the locations of the stars...
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
Interstellar medium
In astronomy, the interstellar medium is the matter that exists in the space between the star systems in a galaxy. This matter includes gas in ionic, atomic, and molecular form, dust, and cosmic rays. It fills interstellar space and blends smoothly into the surrounding intergalactic space...
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.
However, the theory of stellar nucleosynthesis advocated by B2FH would not be very convincing if it could not also detail the nuclear physics
Nuclear physics
Nuclear physics is the field of physics that studies the building blocks and interactions of atomic nuclei. The most commonly known applications of nuclear physics are nuclear power generation and nuclear weapons technology, but the research has provided application in many fields, including those...
and astrophysics
Astrophysics
Astrophysics is the branch of astronomy that deals with the physics of the universe, including the physical properties of celestial objects, as well as their interactions and behavior...
involved. By carefully scrutinizing the table of nuclides
Table of nuclides
The tables listed below provide information on the basic properties of all nuclides.* Neutron + Element 1 - Element 24 * Element 25 - Element 48 * Element 49 - Element 72...
, the authors were able to predict the existence of different stellar environments which could produce the observed isotopic abundances
Abundance of the chemical elements
The abundance of a chemical element measures how relatively common the element is, or how much of the element is present in a given environment by comparison to all other elements...
, 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
P-process
The term p-process is used in two ways in the scientific literature concerning the astrophysical origin of the elements . Originally it referred to a proton capture process which is the source of certain, naturally occurring, proton-rich isotopes of the elements from selenium to mercury...
, r-process
R-process
The r-process is a nucleosynthesis process, likely occurring in core-collapse supernovae responsible for the creation of approximately half of the neutron-rich atomic nuclei that are heavier than iron. The process entails a succession of rapid neutron captures on seed nuclei, typically Ni-56,...
, and s-process
S-process
The S-process or slow-neutron-capture-process is a nucleosynthesis process that occurs at relatively low neutron density and intermediate temperature conditions in stars. Under these conditions the rate of neutron capture by atomic nuclei is slow relative to the rate of radioactive beta-minus decay...
to account for many of the elements heavier than iron
Iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...
, and these ideas have since come to bear much fruit.
Writing of the paper
MargaretMargaret Burbidge
Eleanor Margaret Burbidge, née Peachey, FRS is a British-born American astrophysicist, noted for original research and holding many administrative posts, including director of the Royal Greenwich Observatory....
and Geoffrey Burbidge
Geoffrey Burbidge
Geoffrey Ronald Burbidge FRS was an English astronomy professor, most recently at the University of California, San Diego. He was married to astrophysicist Dr. Margaret Burbidge.-Education:...
wrote the first draft of the paper, deliberately incorporating extensive observations and experimental data to support the theory. Both Hoyle and Fowler
William Alfred Fowler
William Alfred "Willy" Fowler was an American astrophysicist and winner of the Nobel Prize for Physics in 1983. He should not be confused with the British astronomer Alfred 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."
Recognition
Because this work firmly established the field of nuclear astrophysicsNuclear astrophysics
Nuclear astrophysics is an interdisciplinary branch of physics involving close collaboration among researchers in various subfields of nuclear physics and astrophysics, with significant emphasis in areas such as stellar modeling, measurement and theoretical estimation of nuclear reaction rates,...
, William Fowler
William Alfred Fowler
William Alfred "Willy" Fowler was an American astrophysicist and winner of the Nobel Prize for Physics in 1983. He should not be confused with the British astronomer Alfred Fowler....
was awarded half of the 1983 Nobel Prize in Physics
Nobel Prize in Physics
The Nobel Prize in Physics is awarded once a year by the Royal Swedish Academy of Sciences. It is one of the five Nobel Prizes established by the will of Alfred Nobel in 1895 and awarded since 1901; the others are the Nobel Prize in Chemistry, Nobel Prize in Literature, Nobel Peace Prize, and...
for his contributions; some believe that Fred Hoyle
Fred Hoyle
Sir Fred Hoyle FRS was an English astronomer and mathematician noted primarily for his contribution to the theory of stellar nucleosynthesis and his often controversial stance on other cosmological and scientific matters—in particular his rejection of the "Big Bang" theory, a term originally...
also deserved similar recognition for his scholarship on this topic, and contend that his unorthodox views concerning the big bang
Big Bang
The Big Bang theory is the prevailing cosmological model that explains the early development of the Universe. According to the Big Bang theory, the Universe was once in an extremely hot and dense state which expanded rapidly. This rapid expansion caused the young Universe to cool and resulted in...
played a role in his lack of a Nobel Prize
Nobel Prize
The Nobel Prizes are annual international awards bestowed by Scandinavian committees in recognition of cultural and scientific advances. The will of the Swedish chemist Alfred Nobel, the inventor of dynamite, established the prizes in 1895...
.
Geoffrey Burbidge
Geoffrey Burbidge
Geoffrey Ronald Burbidge FRS was an English astronomy professor, most recently at the University of California, San Diego. He was married to astrophysicist Dr. Margaret Burbidge.-Education:...
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 and 1954 as indicators of Hoyle's authorship of the theory of stellar nucleosynthesis
Stellar nucleosynthesis
Stellar nucleosynthesis is the collective term for the nuclear reactions taking place in stars to build the nuclei of the elements heavier than hydrogen. Some small quantity of these reactions also occur on the stellar surface under various circumstances...
. Burbidge explains, "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
Reviews of Modern Physics
The Reviews of Modern Physics is a journal of the American Physical Society. The journal started in paper form. All volumes are also online by subscription.Issue 1, Volume 1 consisted of the review by...
. When B2FH was first written, preprints were widely distributed to the nuclear physics
Nuclear physics
Nuclear physics is the field of physics that studies the building blocks and interactions of atomic nuclei. The most commonly known applications of nuclear physics are nuclear power generation and nuclear weapons technology, but the research has provided application in many fields, including those...
community. Willy Fowler was very well known as a leader in that community, and the California Institute of Technology
California Institute of Technology
The California Institute of Technology is a private research university located in Pasadena, California, United States. Caltech has six academic divisions with strong emphases on science and engineering...
already had a news bureau that knew how to spread the word.
In 2007 a conference was held in Pasadena, California
Pasadena, California
Pasadena is a city in Los Angeles County, California, United States. Although famous for hosting the annual Rose Bowl football game and Tournament of Roses Parade, Pasadena is the home to many scientific and cultural institutions, including the California Institute of Technology , the Jet...
to commemorate the 50th anniversary of the publication of this influential paper.
External links
- B2FH paper (Direct PDF download link). Free to read.