Nucleosynthesis of heavy elements

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Nucleosynthesis of heavy elements

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 found 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.

Big Bang nucleosynthesis - Wikipedia

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.

Nucleosynthesis of heavy elements

Cameronand Donald D. Claytonfollowed by many others. The seminal review paper by E. BurbidgeFowler and Hoyle [5] 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.Whether an isotope is an s-process or r-process element (or both) depends on both its properties and the properties of the isotopes surrounding it.

Big Bang nucleosynthesis produced very few nuclei of elements heavier than lithium due to a bottleneck: the absence of a stable nucleus with 8 or 5 nucleons.

This deficit of larger atoms also limited the amounts of lithium-7 produced during BBN. by neutrino heating, and r-process nucleosynthesis in the neutrino-driven wind of the newly formed neutron star, respectively, as suggested by current computer simulations.

In the upper parts of the figures the dynamical state. We present nucleosynthesis results form calculations that follow the evolution of massive stars from their birth on the main sequence through their explosion as . Neutron Star Mergers and Nucleosynthesis of Heavy Elements Collisions between neutron stars are widely considered to be the source of r-process elements, Friedrich-Karl Thielemann and colleagues write.

The lightest elements (hydrogen, helium, deuterium, lithium) were produced in the Big Bang nucleosynthesis. According to the Big Bang theory, the temperatures in the early universe were so high that fusion reactions could take place.

Supernova nucleosynthesis - Wikipedia