Stellar nucleosynthesis

Stellar nucleosynthesis

Overview
Stellar 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...

is the collective term for the nuclear
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...

 reactions taking place 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 to build the nuclei of the 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...

 heavier than 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...

. Some small quantity of these reactions also occur on the stellar surface under various circumstances. For the creation of elements during the explosion of a star, the term supernova nucleosynthesis
Supernova nucleosynthesis
Supernova nucleosynthesis is the production of new chemical elements inside supernovae. It occurs primarily due to explosive nucleosynthesis during explosive oxygen burning and silicon burning...

 is used.

The processes involved began to be understood early in the 20th century, when it was first realized that the energy
Energy
In physics, energy is an indirectly observed quantity. It is often understood as the ability a physical system has to do work on other physical systems...

 released from nuclear reactions accounted for the longevity of the Sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...

 as a source of heat
Heat
In physics and thermodynamics, heat is energy transferred from one body, region, or thermodynamic system to another due to thermal contact or thermal radiation when the systems are at different temperatures. It is often described as one of the fundamental processes of energy transfer between...

 and light
Light
Light or visible light is electromagnetic radiation that is visible to the human eye, and is responsible for the sense of sight. Visible light has wavelength in a range from about 380 nanometres to about 740 nm, with a frequency range of about 405 THz to 790 THz...

.
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Encyclopedia
Stellar 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...

is the collective term for the nuclear
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...

 reactions taking place 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 to build the nuclei of the 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...

 heavier than 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...

. Some small quantity of these reactions also occur on the stellar surface under various circumstances. For the creation of elements during the explosion of a star, the term supernova nucleosynthesis
Supernova nucleosynthesis
Supernova nucleosynthesis is the production of new chemical elements inside supernovae. It occurs primarily due to explosive nucleosynthesis during explosive oxygen burning and silicon burning...

 is used.

The processes involved began to be understood early in the 20th century, when it was first realized that the energy
Energy
In physics, energy is an indirectly observed quantity. It is often understood as the ability a physical system has to do work on other physical systems...

 released from nuclear reactions accounted for the longevity of the Sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...

 as a source of heat
Heat
In physics and thermodynamics, heat is energy transferred from one body, region, or thermodynamic system to another due to thermal contact or thermal radiation when the systems are at different temperatures. It is often described as one of the fundamental processes of energy transfer between...

 and light
Light
Light or visible light is electromagnetic radiation that is visible to the human eye, and is responsible for the sense of sight. Visible light has wavelength in a range from about 380 nanometres to about 740 nm, with a frequency range of about 405 THz to 790 THz...

. The prime energy producer in the sun is the 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...

 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...

, which occurs at a minimum temperature of 3 million kelvin
Kelvin
The kelvin is a unit of measurement for temperature. It is one of the seven base units in the International System of Units and is assigned the unit symbol K. The Kelvin scale is an absolute, thermodynamic temperature scale using as its null point absolute zero, the temperature at which all...

.

History


In 1920, Arthur Eddington, on the basis of the precise measurements of atoms by F.W. Aston
Francis William Aston
Francis William Aston was a British chemist and physicist who won the 1922 Nobel Prize in Chemistry for his discovery, by means of his mass spectrograph, of isotopes, in a large number of non-radioactive elements, and for his enunciation of the whole-number rule...

, was the first to suggest that stars obtained their energy from 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...

 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 form 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...

.
In 1928, George Gamow
George 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...

 derived what is now called the Gamow factor
Gamow factor
The Gamow Factor or Gamow-Sommerfeld Factor, named after its discoverer George Gamow, is a probability factor for two nuclear particles' chance of overcoming the Coulomb barrier in order to undergo nuclear reactions, for example in nuclear fusion...

, a quantum-mechanical
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...

 formula that gave the probability of bringing two nuclei sufficiently close for the strong nuclear force to overcome the Coulomb barrier
Coulomb barrier
The Coulomb barrier, named after Coulomb's law, which is named after physicist Charles-Augustin de Coulomb , is the energy barrier due to electrostatic interaction that two nuclei need to overcome so they can get close enough to undergo a nuclear reaction...

.
The Gamow factor was used in the decade that followed by Atkinson
Robert d'Escourt Atkinson
Robert d'Escourt Atkinson was a British astronomer, physicist and inventor.-Biography:...

 and Houtermans
Fritz Houtermans
Friedrich Georg "Fritz" Houtermans was a Dutch-Austrian-German atomic and nuclear physicist born in Zoppot near Danzig, West Prussia...

 and later by Gamow himself and Edward Teller
Edward Teller
Edward Teller was a Hungarian-American theoretical physicist, known colloquially as "the father of the hydrogen bomb," even though he did not care for the title. Teller made numerous contributions to nuclear and molecular physics, spectroscopy , and surface physics...

 to derive the rate at which nuclear reactions would proceed at the high temperatures believed to exist in stellar interiors.

In 1939, in a paper entitled "Energy Production in Stars", 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...

 analyzed the different possibilities for reactions by which hydrogen is fused into helium. He selected two processes that he believed to be the sources of energy in stars. The first one, the proton-proton chain, is the dominant energy source in stars with masses up to about the mass of the Sun. The second process, the carbon-nitrogen-oxygen 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...

, which was also considered by Carl Friedrich 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...

 in 1938, is most important in more massive stars. These works concerned the energy generation capable of keeping stars hot. They did not address the creation of heavier nuclei, however. That theory was begun by 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...

 in 1946 with his argument that a collection of very hot nuclei would assemble into 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...

. Hoyle followed that in 1954 with a large paper outlining how advanced fusion stages within stars would synthesize elements between carbon and iron in mass.

Quickly, many important omissions in Hoyle's theory were corrected, beginning with the publication of a celebrated review paper in 1957 by Burbidge
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....

, 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:...

, 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 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...

 (commonly referred to as the B2FH paper). This latter work collected and refined earlier research into a heavily cited picture that gave promise of accounting for the observed relative abundances of the elements. Significant improvements were made by A. G. W. Cameron
Alastair GW Cameron
Alastair G. W. Cameron was a Canadian astrophysicist and space scientist who was an eminent staff member of the Astronomy department of Harvard University. Cameron, the son of a Canadian biochemist, was born in Winnipeg...

 and by Donald D. Clayton. Cameron presented his own independent approach (following Hoyle) of nucleosynthesis. He introduced computers into time-dependent calculations of evolution of nuclear systems. Clayton calculated the first time-dependent models of the 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...

, the 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,...

, the burning of silicon into iron-group elements, and discovered radiogenic chronologies for determining the age of the elements. The entire research field expanded rapidly in the 1970s.

Key reactions


The most important reactions in stellar nucleosynthesis:
  • 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...

     burning:
    • The deuterium burning
      Deuterium burning
      Deuterium burning is a nuclear fusion reaction that occurs in stars and some substellar objects, in which a deuterium nucleus and a proton combine to form a helium-3 nucleus...

    • The proton-proton chain
    • The carbon-nitrogen-oxygen 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...

  • 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...

     burning:
    • The triple-alpha process
      Triple-alpha process
      The triple alpha process is a set of nuclear fusion reactions by which three helium-4 nuclei are transformed into carbon.Older stars start to accumulate helium produced by the proton–proton chain reaction and the carbon–nitrogen–oxygen cycle in their cores...

    • The alpha process
  • Burning of heavier elements:
    • Carbon burning process
      Carbon burning process
      The carbon-burning process or carbon fusion is a set of nuclear fusion reactions that take place in massive stars that have used up the lighter elements in their cores...

    • Neon burning process
      Neon burning process
      The neon-burning process is a set of nuclear fusion reactions that take place in massive stars . Neon burning requires high temperatures and densities ....

    • Oxygen burning process
      Oxygen burning process
      The oxygen-burning process is a set of nuclear fusion reactions that take place in massive stars that have used up the lighter elements in their cores. It occurs at temperatures around 1.5×109 K / 130 keV and densities of 1010 kg/m3....

    • Silicon burning process
      Silicon burning process
      In astrophysics, silicon burning is a very brief sequence of nuclear fusion reactions that occur in massive stars with a minimum of about 8–11 solar masses. Silicon burning is the final stage of fusion for massive stars that have run out of the fuels that power them for their long lives in the main...

  • Production of 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...

    :
    • Neutron
      Neutron
      The neutron is a subatomic hadron particle which has the symbol or , no net electric charge and a mass slightly larger than that of a proton. With the exception of hydrogen, nuclei of atoms consist of protons and neutrons, which are therefore collectively referred to as nucleons. The number of...

       capture:
      • The 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,...

      • The 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...

    • Proton capture:
      • The Rp-process
        Rp-process
        The rp-process consists of consecutive proton captures onto seed nuclei to produce heavier elements. It is a nucleosynthesis process and, along with the s process and the r process, may be responsible for the generation of many of the heavy elements present in the universe...

    • Photo-disintegration
      Photodisintegration
      Photodisintegration is a physical process in which an extremely high energy gamma ray interacts with an atomic nucleus and causes it to enter an excited state, which immediately decays by emitting a subatomic particle. A single proton or neutron is effectively knocked out of the nucleus by the...

      :
      • 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...


External links

  • How the Sun Shines by John N. Bahcall
    John N. Bahcall
    John Norris Bahcall was an American astrophysicist, best known for his contributions to the solar neutrino problem, the development of the Hubble Space Telescope and for his leadership and development of the Institute for Advanced Study in Princeton.-Early and family life:Bahcall was born in...

  • Nucleosynthesis in NASA
    NASA
    The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...

    's Cosmicopia