Editing Nucleosynthesis (section)

==Major types==

===Big Bang nucleosynthesis===
{{main|Big Bang nucleosynthesis}}
Big Bang nucleosynthesis<ref>{{Cite web |title=23. Big-Bang Nucleosynthesis |date=September 2017  |first1=B.D. |last1=Fields |first2=P. |last2=Molaro |first3=S. |last3=Sarkar |citeseerx=10.1.1.729.1183 |url=https://pdg.lbl.gov/2017/mobile/reviews/pdf/rpp2017-rev-bbang-nucleosynthesis-m.pdf |archive-url=https://web.archive.org/web/20220401065230/https://pdg.lbl.gov/2017/mobile/reviews/pdf/rpp2017-rev-bbang-nucleosynthesis-m.pdf |archive-date=2022-04-01 |url-status=live   }}</ref> occurred within the first three minutes of the beginning of the universe and is responsible for much of the abundance of {{chem|1|H}} ([[hydrogen-1|protium]]), {{chem|2|H}} (D, [[deuterium]]), {{chem|3|He}} ([[helium-3]]), and {{chem|4|He}} ([[helium-4]]). Although {{chem|4|He}} continues to be produced by stellar fusion and [[alpha decay]]s and trace amounts of {{chem|1|H}} continue to be produced by [[spallation]] and certain types of radioactive decay, most of the mass of the isotopes in the universe are thought to have been produced in the Big Bang. The nuclei of these elements, along with some {{chem|7|Li}} and {{chem|7|Be}} are considered to have been formed between 100 and 300 seconds after the Big Bang when the primordial [[quark–gluon plasma]] froze out to form protons and neutrons. Because of the very short period in which nucleosynthesis occurred before it was stopped by expansion and cooling (about 20 minutes), no elements heavier than [[beryllium]] (or possibly [[boron]]) could be formed. Elements formed during this time were in the plasma state, and did not cool to the state of neutral atoms until much later.{{citation needed|date=December 2012}}

{{Image frame|align=center|width=400|caption=Chief nuclear reactions responsible for the [[abundance of the chemical elements|relative abundances]] of light [[atomic nucleus|atomic nuclei]] observed throughout the universe.
|content=<math chem>\begin{array}{ll}
\ce{n^0 -> p+{} + e^-{} + \overline{\nu}_e} & \ce{p+{} + n^0 -> ^2_1D{} + \gamma}\\
\ce{^2_1D{} + p+ -> ^3_2He{} + \gamma} & \ce{^2_1D{} + ^2_1D -> ^3_2He{} + n^0}\\
\ce{^2_1D{} + ^2_1D -> ^3_1T{} + p+} & \ce{^3_1T{} + ^2_1D -> ^4_2He{} + n^0}\\
\ce{^3_1T{} + ^4_2He -> ^7_3Li{} + \gamma} & \ce{^3_2He{} + n^0 -> ^3_1T{} + p+}\\
\ce{^3_2He{} + ^2_1D -> ^4_2He{} + p+} & \ce{^3_2He{} + ^4_2He -> ^7_4Be{} + \gamma}\\
\ce{^7_3Li{} + p+ -> ^4_2He{} + ^4_2He} & \ce{^7_4Be{} + n^0 -> ^7_3Li{} + p+}
\end{array}</math>}}

===Stellar nucleosynthesis===
{{Main|Stellar nucleosynthesis|Proton–proton chain|Triple-alpha process|CNO cycle|s-process|p-process|photodisintegration}}

Stellar nucleosynthesis is the nuclear process by which new nuclei are produced. It occurs in stars during [[stellar evolution]]. It is responsible for the galactic abundances of elements from carbon to iron. Stars are thermonuclear furnaces in which H and He are fused into heavier nuclei by increasingly high temperatures as the composition of the core evolves.<ref>{{cite book |last1=Clayton |first1=D. D. |year=1983 |title=Principles of Stellar Evolution and Nucleosynthesis |url=https://archive.org/details/principlesofstel0000clay/page/ |url-access=registration |at=[https://archive.org/details/principlesofstel0000clay/page/ Chapter 5] |edition=Reprint |publisher=[[University of Chicago Press]] |location=Chicago, IL|isbn=978-0-226-10952-7 }}</ref> Of particular importance is carbon because its formation from He is a bottleneck in the entire process. Carbon is produced by the [[triple-alpha process]] in all stars. Carbon is also the main element that causes the release of free neutrons within stars, giving rise to the s-process, in which the slow absorption of neutrons converts iron into elements heavier than iron and nickel.<ref>{{cite journal |last1=Clayton |first1=D. D. |last2=Fowler |first2=W. A. |last3=Hull |first3=T. E. |last4=Zimmerman |first4=B. A. |title=Neutron Capture Chains in Heavy Element Synthesis |journal=[[Annals of Physics]] |date=1961 |volume=12 |issue=3 |pages=331–408 |doi=10.1016/0003-4916(61)90067-7|bibcode=1961AnPhy..12..331C }}</ref><ref name=ClaytonIsotopes7>{{cite book |last1=Clayton |first1=D. D. |year=1983 |title=Principles of Stellar Evolution and Nucleosynthesis |url=https://archive.org/details/principlesofstel0000clay/page/ |url-access=registration |at=[https://archive.org/details/principlesofstel0000clay/page/ Chapter 7] |edition=Reprint |publisher=[[University of Chicago Press]] |location=Chicago, IL|isbn=978-0-226-10952-7 }}</ref>

The products of stellar nucleosynthesis are generally dispersed into the interstellar gas through mass loss episodes and the stellar winds of low mass stars. The mass loss events can be witnessed today in the [[planetary nebula]]e phase of low-mass star evolution, and the explosive ending of stars, called [[supernova]]e, of those with more than eight times the mass of the Sun.

The first direct proof that nucleosynthesis occurs in stars was the astronomical observation that interstellar gas has become enriched with heavy elements as time passed. As a result, stars that were born from it late in the galaxy, formed with much higher initial heavy element abundances than those that had formed earlier. The detection of [[technetium]] in the atmosphere of a [[red giant]] star in 1952,<ref>{{cite journal |last1=Merrill |first1=S. P. W. |date=1952 |title=Spectroscopic Observations of Stars of Class |journal=[[The Astrophysical Journal]] |volume=116 |pages=21 |bibcode=1952ApJ...116...21M |doi=10.1086/145589}}</ref> by spectroscopy, provided the first evidence of nuclear activity within stars. Because technetium is radioactive, with a half-life much less than the age of the star, its abundance must reflect its recent creation within that star. Equally convincing evidence of the stellar origin of heavy elements is the large overabundances of specific stable elements found in stellar atmospheres of [[asymptotic giant branch]] stars. Observation of barium abundances some 20–50 times greater than found in unevolved stars is evidence of the operation of the s-process within such stars. Many modern proofs of stellar nucleosynthesis are provided by the [[isotopes|isotopic]] compositions of [[Cosmic dust#Stardust|stardust]], solid grains that have condensed from the gases of individual stars and which have been extracted from meteorites. Stardust is one component of [[cosmic dust]] and is frequently called [[presolar grains]]. The measured isotopic compositions in stardust grains demonstrate many aspects of nucleosynthesis within the stars from which the grains condensed during the star's late-life mass-loss episodes.<ref name=Clayton2004>{{cite journal |last1=Clayton |first1=D. D. |last2=Nittler |first2=L. R. |title=Astrophysics with Presolar Stardust |journal=[[Annual Review of Astronomy and Astrophysics]] |date=2004 |volume=42 |issue=1 |pages=39–78 |bibcode=2004ARA&A..42...39C |doi=10.1146/annurev.astro.42.053102.134022}}</ref>

===Explosive nucleosynthesis===

{{Main|r-process|rp-process|Supernova nucleosynthesis}}

[[Supernova nucleosynthesis]] occurs in the energetic environment in supernovae, in which the elements between silicon and nickel are synthesized in quasiequilibrium<ref name=Bodansky1968>{{cite journal |last1=Bodansky |first1=D. |last2=Clayton |first2=D. D. |last3=Fowler |first3=W. A. |date=1968 |title=Nuclear Quasi-Equilibrium during Silicon Burning |journal=[[The Astrophysical Journal Supplement Series]] |volume=16 |pages=299 |bibcode=1968ApJS...16..299B |doi=10.1086/190176|url=https://tigerprints.clemson.edu/cgi/viewcontent.cgi?article=1311&context=physastro_pubs }}</ref> established during fast fusion that attaches by reciprocating balanced nuclear reactions to <sup>28</sup>Si. Quasiequilibrium can be thought of as ''almost equilibrium'' except for a high abundance of the <sup>28</sup>Si nuclei in the feverishly burning mix. This concept<ref name=ClaytonIsotopes7/> was the most important discovery in nucleosynthesis theory of the intermediate-mass elements since Hoyle's 1954 paper because it provided an overarching understanding of the abundant and chemically important elements between silicon (''A'' = 28) and nickel (''A'' = 60). It replaced the incorrect although much cited [[alpha process]] of the [[B2FH paper|B<sup>2</sup>FH paper]], which inadvertently obscured Hoyle's 1954 theory.<ref>{{cite journal |last1=Clayton |first1=D. D. |title=Hoyle's Equation |journal=[[Science (journal)|Science]] |date=2007 |volume=318 |issue=5858 |pages=1876–1877 |doi=10.1126/science.1151167|pmid=18096793 |s2cid=118423007 }}</ref> Further nucleosynthesis processes can occur, in particular the r-process (rapid process) described by the B<sup>2</sup>FH paper and first calculated by Seeger, Fowler and Clayton,<ref>{{cite journal |last1=Seeger |first1=P. A. |last2=Fowler |first2=W. A. |last3=Clayton |first3=D. D. |date=1965 |title=Nucleosynthesis of Heavy Elements by Neutron Capture |journal=[[The Astrophysical Journal Supplement Series]] |volume=11 |pages=121 |bibcode=1965ApJS...11..121S |doi=10.1086/190111|url=http://tigerprints.clemson.edu/cgi/viewcontent.cgi?article=1307&context=physastro_pubs }}</ref> in which the most neutron-rich isotopes of elements heavier than nickel are produced by rapid absorption of free neutrons. The creation of free neutrons by [[electron capture]] during the rapid compression of the supernova core along with the assembly of some neutron-rich seed nuclei makes the r-process a ''primary process'', and one that can occur even in a star of pure H and He. This is in contrast to the B<sup>2</sup>FH designation of the process as a ''secondary process''. This promising scenario, though generally supported by supernova experts, has yet to achieve a satisfactory calculation of r-process abundances. The primary r-process has been confirmed by astronomers who had observed old stars born when galactic [[metallicity]] was still small, that nonetheless contain their complement of r-process nuclei; thereby demonstrating that the metallicity is a product of an internal process. The r-process is responsible for our natural cohort of radioactive elements, such as uranium and thorium, as well as the most neutron-rich isotopes of each heavy element.

The [[rp-process]] (rapid proton) involves the rapid absorption of free protons as well as neutrons, but its role and its existence are less certain.

Explosive nucleosynthesis occurs too rapidly for radioactive decay to decrease the number of neutrons, so that many abundant isotopes with equal and even numbers of protons and neutrons are synthesized by the silicon quasi-equilibrium process.<ref name=Bodansky1968/> During this process, the burning of oxygen and silicon fuses nuclei that themselves have equal numbers of protons and neutrons to produce nuclides which consist of whole numbers of helium nuclei, up to 15 (representing <sup>60</sup>Ni). Such multiple-alpha-particle nuclides are totally stable up to <sup>40</sup>Ca (made of 10 helium nuclei), but heavier nuclei with equal and even numbers of protons and neutrons are tightly bound but unstable. The quasi-equilibrium produces radioactive [[isobar (nuclide)|isobars]] [[titanium-44|<sup>44</sup>Ti]], <sup>48</sup>Cr, <sup>52</sup>Fe, and <sup>56</sup>Ni, which (except <sup>44</sup>Ti) are created in abundance but decay after the explosion and leave the most stable isotope of the corresponding element at the same atomic weight. The most abundant and extant isotopes of elements produced in this way are <sup>48</sup>Ti, <sup>52</sup>Cr, and <sup>56</sup>Fe. These decays are accompanied by the emission of gamma-rays (radiation from the nucleus), whose [[spectroscopic lines]] can be used to identify the isotope created by the decay. The detection of these emission lines were an important early product of gamma-ray astronomy.<ref name=Clayton1969>{{cite journal |last1=Clayton |first1=D. D. |last2=Colgate |first2=S. A. |last3=Fishman |first3=G. J. |date=1969 |title=Gamma-Ray Lines from Young Supernova Remnants |journal=[[The Astrophysical Journal]] |volume=155 |pages=75 |bibcode=1969ApJ...155...75C |doi=10.1086/149849|url=https://tigerprints.clemson.edu/cgi/viewcontent.cgi?article=1313&context=physastro_pubs }}</ref>

The most convincing proof of explosive nucleosynthesis in supernovae occurred in 1987 when those gamma-ray lines were detected emerging from [[supernova 1987A]]. Gamma-ray lines identifying <sup>56</sup>Co and <sup>57</sup>Co nuclei, whose half-lives limit their age to about a year, proved that their radioactive cobalt parents created them. This nuclear astronomy observation was predicted in 1969<ref name=Clayton1969/> as a way to confirm explosive nucleosynthesis of the elements, and that prediction played an important role in the planning for NASA's [[Compton Gamma Ray Observatory|Compton Gamma-Ray Observatory]].

Other proofs of explosive nucleosynthesis are found within the stardust grains that condensed within the interiors of supernovae as they expanded and cooled. Stardust grains are one component of cosmic dust. In particular, radioactive <sup>44</sup>Ti was measured to be very abundant within supernova stardust grains at the time they condensed during the supernova expansion.<ref name=Clayton2004/> This confirmed a 1975 prediction of the identification of supernova stardust (SUNOCONs), which became part of the pantheon of [[presolar grains]]. Other unusual isotopic ratios within these grains reveal many specific aspects of explosive nucleosynthesis.

Another type of explosive nucleosynthesis through the r-process was suggested in the flaring of [[Magnetar|magnetars]]. Some direct evidence for this was published in 2025. It is estimated that this kind of events has created ~1%–10% of the heavier elements in the universe.<ref>{{Cite journal |last1=Patel |first1=Anirudh |last2=Metzger |first2=Brian D. |last3=Cehula |first3=Jakub |last4=Burns |first4=Eric |last5=Goldberg |first5=Jared A. |last6=Thompson |first6=Todd A. |date=April 2025 |title=Direct Evidence for r-process Nucleosynthesis in Delayed MeV Emission from the SGR 1806–20 Magnetar Giant Flare |journal=The Astrophysical Journal Letters |language=en |volume=984 |issue=1 |pages=L29 |doi=10.3847/2041-8213/adc9b0 |doi-access=free |arxiv=2501.09181 |bibcode=2025ApJ...984L..29P |issn=2041-8205}}</ref>

===Neutron star mergers===
The [[Neutron star collision|merger]] of binary neutron stars (BNSs) is now believed to be the main source of r-process elements.<ref>{{cite web |last=Stromberg |first=Joseph |date=16 July 2013 |title=All the Gold in the Universe Could Come from the Collisions of Neutron Stars |url=http://www.smithsonianmag.com/science-nature/all-the-gold-in-the-universe-could-come-from-the-collisions-of-neutron-stars-13474145/?page=1 |work=[[Smithsonian (magazine)|Smithsonian]] |access-date=27 April 2014}}</ref> Being neutron-rich by definition, mergers of this type had been suspected of being a source of such elements, but definitive evidence was difficult to obtain. In 2017 strong evidence emerged, when [[LIGO]], [[Virgo interferometer|VIRGO]], the [[Fermi Gamma-ray Space Telescope]] and [[INTEGRAL]], along with a collaboration of many observatories around the world, detected both [[gravitational wave]] and electromagnetic signatures of a likely neutron star merger, [[GW170817]], and subsequently detected signals of numerous heavy elements such as gold as the ejected [[Degenerate matter#Neutron degeneracy|degenerate matter]] decays and cools.<ref>{{cite web |last=Chu |first=J. |date=n.d. |url=https://www.ligo.caltech.edu/page/press-release-gw170817 |title=GW170817 Press Release |publisher=[[LIGO]]/[[Caltech]] |access-date=2018-07-04}}</ref> The first detection of the merger of a neutron star and black hole (NSBHs) came in July 2021 and more after but analysis seem to favor BNSs over NSBHs as the main contributors to heavy metal production.<ref>{{Cite journal|last1=Chen|first1=Hsin-Yu|last2=Vitale|first2=Salvatore|last3=Foucart|first3=Francois|date=2021-10-01|title=The Relative Contribution to Heavy Metals Production from Binary Neutron Star Mergers and Neutron Star–Black Hole Mergers|journal=The Astrophysical Journal Letters|volume=920|issue=1|pages=L3|doi=10.3847/2041-8213/ac26c6|arxiv=2107.02714 |bibcode=2021ApJ...920L...3C |s2cid=238198587 |issn=2041-8205|doi-access=free}}</ref><ref>{{Cite web|title=Neutron star collisions are a "goldmine" of heavy elements, study finds|url=https://news.mit.edu/2021/neutron-star-collisions-goldmine-heavy-elements-1025|access-date=2021-12-23|website=MIT News {{!}} Massachusetts Institute of Technology|date=25 October 2021 |language=en}}</ref>

===Black hole accretion disk nucleosynthesis===
Nucleosynthesis may happen in [[accretion disk]]s of [[black hole]]s.<ref>{{cite journal |last1=Chakrabarti |first1=S. K. |last2=Jin |first2=L. |last3=Arnett |first3=W. D. |date=1987 |title=Nucleosynthesis Inside Thick Accretion Disks Around Black Holes. I – Thermodynamic Conditions and Preliminary Analysis |journal=[[The Astrophysical Journal]] |volume=313 |pages=674 |doi=10.1086/165006 |bibcode=1987ApJ...313..674C |osti=6468841}}</ref><ref>{{cite web |last1=McLaughlin |first1=G. | author1-link = Gail McLaughlin |last2=Surman |first2=R. |date=2 April 2007 |title=Nucleosynthesis from Black Hole Accretion Disks |url=https://wwwmpa.mpa-garching.mpg.de/~grb07/Presentations/McLaughlin.pdf |archive-url=https://web.archive.org/web/20160910224940/http://wwwmpa.mpa-garching.mpg.de/~grb07/Presentations/McLaughlin.pdf |archive-date=2016-09-10 |url-status=live}}</ref><ref>{{cite thesis |last=Frankel |first=N. |year=2017 |title=Nucleosynthesis in Accretion Disks Around Black Holes |url=https://lup.lub.lu.se/student-papers/record/8912003/file/8912097.pdf |archive-url=https://web.archive.org/web/20200324192549/http://lup.lub.lu.se/student-papers/record/8912003/file/8912097.pdf |archive-date=2020-03-24 |url-status=live |type=MSc |publisher=[[Lund Observatory]]/[[Lund University]] }}</ref><ref>{{cite journal |last1=Surman |first1=R. |last2=McLaughlin |first2=G. C. | author2-link = Gail McLaughlin |last3=Ruffert |first3=M. |last4=Janka |first4=H.-Th. |last5=Hix |first5=W. R. |date=2008 |title=Process Nucleosynthesis in Hot Accretion Disk Flows from Black Hole-Neutron Star Mergers |journal=[[The Astrophysical Journal]] |volume=679 |issue=2 |pages=L117–L120 |arxiv=0803.1785 |bibcode=2008ApJ...679L.117S |doi=10.1086/589507|s2cid=17114805 }}</ref><ref>{{cite journal |last1=Arai |first1=K. |last2=Matsuba |first2=R. |last3=Fujimoto |first3=S. |last4=Koike |first4=O. |last5=Hashimoto |first5=M. |date=2003 |title=Nucleosynthesis Inside Accretion Disks Around Intermediate-mass Black Holes |journal=[[Nuclear Physics A]] |volume=718 |pages=572–574 |bibcode=2003NuPhA.718..572A |doi=10.1016/S0375-9474(03)00856-X}}</ref><ref>{{cite book |last=Mukhopadhyay |first=B. |year=2018 |chapter=Nucleonsynthesis in Advective Accretion Disk Around Compact Object |chapter-url=https://books.google.com/books?id=dOMNhyivg1MC&pg=PA2261 |editor-last1=Jantzen |editor-first1=R. T. |editor-last2=Ruffini |editor-first2=R. |editor-last3=Gurzadyan |editor-first3=V. G. |title=Proceedings of the Ninth Marcel Grossmann Meeting on General Relavitity |pages=2261–2262 |publisher=[[World Scientific]] |doi=10.1142/9789812777386_0544 |isbn=9789812389930|citeseerx=10.1.1.254.7490 |arxiv=astro-ph/0103162 |bibcode=  2002nmgm.meet.2261M|s2cid=118008078 }}</ref><ref>{{cite journal |last1=Breen |first1=P. G. |date=2018 |title=Light element variations in globular clusters via nucleosynthesis in black hole accretion discs |journal=[[Monthly Notices of the Royal Astronomical Society: Letters]] |volume=481 |issue= 1|pages=L110–114 |doi=10.1093/mnrasl/sly169 |doi-access=free |bibcode=2018MNRAS.481L.110B |arxiv=1804.08877 |s2cid=54001706 }}</ref>

===Cosmic ray spallation===
{{main|Cosmic ray spallation}}
Cosmic ray spallation process reduces the atomic weight of interstellar matter by the impact with cosmic rays, to produce some of the lightest elements present in the universe (though not a significant amount of [[deuterium]]). Most notably spallation is believed to be responsible for the generation of almost all of <sup>3</sup>He and the elements [[lithium]], [[beryllium]], and boron, although some {{SimpleNuclide|Lithium|7}} and {{SimpleNuclide|Beryllium|7}} are thought to have been produced in the Big Bang. The spallation process results from the impact of [[cosmic rays]] (mostly fast protons) against the [[interstellar medium]]. These impacts fragment carbon, nitrogen, and oxygen nuclei present. The process results in the light elements beryllium, boron, and lithium in the cosmos at much greater abundances than they are found within solar atmospheres. The quantities of the light elements <sup>1</sup>H and <sup>4</sup>He produced by spallation are negligible relative to their primordial abundance.

Beryllium and boron are not significantly produced by stellar fusion processes, since [[beryllium-8|<sup>8</sup>Be]] has an extremely short half-life of {{val|8.2|e=-17}} seconds.<ref>{{cite journal |title=A New Approach for Calculating the Alpha-Decay Half-Life for the Heavy and Super-heavy Elements and an Exact A Priori Result for Beyllium-8 |url=https://www.osti.gov/servlets/purl/1773479 |website=osti.gov |date=2021 |publisher=U.S. Department of Energy Office of Scientific and Technical Information |doi=10.2172/1773479 |access-date=17 April 2024 |last1=Surdoval |first1=Wayne |last2=Berry |first2=David |osti=1773479 }}</ref>