In astronomy — and astrophysics and cosmology — there are two main kinds of nucleosynthesis, Big Bang nucleosynthesis BBNand stellar nucleosynthesis. In the amazingly successful set of theories which are popularly called the Big Bang theory, the early universe was very dense, and very hot. The universe continued to cool, and soon became too cold for any further nuclear reactions … the unstable isotopes left then decayed, as did the neutrons not already in some nucleus or other. Most matter was then hydrogen actually just protons; the electrons were not captured to form atoms until much laterand helium-4 alpha particles … with a sprinkling of deuterium, a dash of helium-3, and a trace of lithium
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 What is nucleosynthesis in stars 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. 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.
Hydrogen and helium are most common, residuals within the paradigm of the Big Bang. The two general trends in the remaining stellar-produced elements are: Processes[ edit ] There are a number of astrophysical processes which are believed to be responsible for nucleosynthesis.
The majority of these occur in within stars, and the chain of those nuclear fusion processes are known as hydrogen burning via the proton-proton chain or the CNO cyclehelium burningcarbon burningneon burningoxygen burning and silicon burning. These processes are able to create elements up to and including iron and nickel.33 rows · Big Bang nucleosynthesis produced no elements heavier than lithium.
To do that you need . That’s BBN. The atoms in your body – apart from the hydrogen – were all made in stars by stellar nucleosynthesis. Stars on the main sequence get the energy they shine by from nuclear. Download the transcript. Astronomy Cast Episode Nucleosynthesis: Elements from Stars.
Fraser Cain: I hope everyone by now has heard our little surprise for the feed, which is that we’ve doubled the amount of Astronomy Casts. So if you like that great, if you don’t like that, let us know. Below you will find a very simplified overview of nucleosynthesis, the process by which elements are formed in the burning hearts of stars.
For additional information, start here. Solar system elemental abundance. Image credit: Ringwood, Stellar nucleosynthesis is the collective term for the nuclear reactions taking place in stars to build the nuclei of the heavier elements.
The processes involved began to be understood early in. Stellar nucleosynthesis is the theory explaining the creation (nucleosynthesis) of chemical elements by nuclear fusion reactions between atoms within the stars.
Stellar nucleosynthesis has occurred continuously since the original creation of hydrogen, helium and lithium during the Big Bang. It is a highly predictive theory that today yields.