This should not be confused with the combustion of hydrogen in an oxidizing atmosphere. There are two predominant processes by which stellar hydrogen burning occurs.
Timeline[ edit ] Periodic table showing the cosmogenic origin of each element.
Elements from carbon up to sulfur may be made in small stars by the alpha process. Elements beyond iron are made in large stars with slow neutron capture s-processfollowed by expulsion to space in gas ejections see planetary nebulae.
Elements heavier than iron may be made in neutron star mergers or supernovae after the r-processinvolving a dense burst of neutrons and rapid capture by the element. It is thought that the primordial nucleons themselves were formed from the quark—gluon plasma during the Big Bang as it cooled below two trillion degrees.
A few minutes afterward, starting with only protons and neutronsnuclei up to lithium and beryllium both with mass number 7 were formed, but the abundances of other elements dropped sharply with growing atomic mass.
Some boron may have been formed at this time, but the process stopped before significant carbon could be formed, as this element requires a far higher product of helium density and time than were present in the short nucleosynthesis period of the Big Bang.
That fusion process essentially shut down at about 20 minutes, due to drops in temperature and density as the universe continued to expand. This first process, Big Bang nucleosynthesiswas the first type of nucleogenesis to occur in the universe. The subsequent nucleosynthesis of the heavier elements requires the extreme temperatures and pressures found within stars and supernovas.
These processes began as hydrogen and helium from the Big Bang collapsed into the first stars at million years. Star formation has occurred continuously in galaxies since that time. Among the elements Stellar nucleosynthesis process naturally on Earth the so-called primordial elementsthose heavier than boron were created by stellar nucleosynthesis and by supernova nucleosynthesis.
Synthesis of these elements occurred either by nuclear fusion including both rapid and slow multiple neutron capture or to a lesser degree by nuclear fission followed by beta decay.
A star gains heavier elements by combining its lighter nuclei, hydrogendeuteriumberylliumlithiumand boronwhich were found in the initial composition of the interstellar medium and hence the star. Interstellar gas therefore contains declining abundances of these light elements, which are present only by virtue of their nucleosynthesis during the Big Bang.
Larger quantities of these lighter elements in the present universe are therefore thought to have been restored through billions of years of cosmic ray mostly high-energy proton mediated breakup of heavier elements in interstellar gas and dust.
The fragments of these cosmic-ray collisions include the light elements Li, Be and B. History of nucleosynthesis theory[ edit ] The first ideas on nucleosynthesis were simply that the chemical elements were created at the beginning of the universe, but no rational physical scenario for this could be identified.
Gradually it became clear that hydrogen and helium are much more abundant than any of the other elements. At the same time it was clear that oxygen and carbon were the next two most common elements, and also that there was a general trend toward high abundance of the light elements, especially those composed of whole numbers of helium-4 nuclei.
Arthur Stanley Eddington first suggested inthat stars obtain their energy by fusing hydrogen into helium and raised the possibility that the heavier elements may also form in stars.
In the years immediately before World War II, Hans Bethe first elucidated those nuclear mechanisms by which hydrogen is fused into helium.
Fred Hoyle 's original work on nucleosynthesis of heavier elements in stars, occurred just after World War II. Hoyle proposed that hydrogen is continuously created in the universe from vacuum and energy, without need for universal beginning. Hoyle's work explained how the abundances of the elements increased with time as the galaxy aged.
Subsequently, Hoyle's picture was expanded during the s by contributions from William A. FowlerAlastair G. Cameronand Donald D. Claytonfollowed by many others. The seminal review paper by E. BurbidgeFowler and Hoyle  is a well-known summary of the state of the field in That paper defined new processes for the transformation of one heavy nucleus into others within stars, processes that could be documented by astronomers.
This would bring all the mass of the Universe to a single point, a "primeval atom", to a state before which time and space did not exist. The goal of the theory of nucleosynthesis is to explain the vastly differing abundances of the chemical elements and their several isotopes from the perspective of natural processes.
The primary stimulus to the development of this theory was the shape of a plot of the abundances versus the atomic number of the elements.
Those abundances, when plotted on a graph as a function of atomic number, have a jagged sawtooth structure that varies by factors up to ten million.
A very influential stimulus to nucleosynthesis research was an abundance table created by Hans Suess and Harold Urey that was based on the unfractionated abundances of the non-volatile elements found within unevolved meteorites. See Handbook of Isotopes in the Cosmos for more data and discussion of abundances of the isotopes.Stellar nucleosynthesis is the process by which elements are created within stars by combining the protons and neutrons together from the nuclei of lighter elements.
All of the atoms in the universe began as hydrogen. Fusion inside stars transforms hydrogen into helium, heat, and radiation. Stellar nucleosynthesis is the collective term for the nuclear reactions taking place in stars to build the nuclei of the heavier elements.
The models for this process are called the s-process and the r-process depending on whether the process proceeds slowly or rapidly. Principles of Stellar Evolution and Nucleosynthesis.
Nucleosynthesis is the process that creates new atomic nuclei from pre-existing nucleons, primarily protons and neutrons. The first nuclei were formed about three minutes after the Big Bang, through the process called Big Bang nucleosynthesis. Stellar Nucleosynthesis: Where Did Heavy Elements Come From?. Acts & Facts. 47 (1). Stellar Nucleosynthesis the number of protons in the nucleus. A theory of nucleosynthesis should explain this pattern. One believes, of course, that all but the lightest elements (Z > 4) are made in since this is a three-body process, its rate is negligible except at high density (and high temperature, T ∼ K). Actually, the triple.
Chicago: University of Chicago Press, Ota, N. Stellar Nucleosynthesis: Where Did Heavy Elements Come From?. Acts & Facts. 47 (1). Stellar Nucleosynthesis Chapter index in this window — — Chapter index in separate window This material (including images) is copyrighted!.
See my copyright notice for fair use practices. Hydrogen and helium and some lithium, boron, and beryllium were created when the universe was created.
Stellar Nucleosynthesis the number of protons in the nucleus. A theory of nucleosynthesis should explain this pattern. One believes, of course, that all but the lightest elements (Z > 4) are made in since this is a three-body process, its rate is negligible except at high density (and high temperature, T ∼ K).
Actually, the triple. Stellar nucleosynthesis is the process by which the natural abundances of the chemical elements within stars change due to nuclear fusion reactions in the cores and their overlying mantles. Stars are said to evolve (age) with changes in the abundances of the elements within.