Stellar nucleosynthesis

In <a href="/facts/Astrophysics/krFPRWLA">astrophysics</a>, stellar nucleosynthesis is the <a href="/facts/Nucleosynthesis/F9MIeADF">creation</a> of <a href="/facts/Chemical_element/0jducgWD">chemical elements</a> by <a href="/facts/Nuclear_fusion/hP0gLDqj">nuclear fusion</a> reactions within <a href="/facts/Star/PFbd6ICx">stars</a>. Stellar nucleosynthesis has occurred since the <a href="/facts/Big_Bang_nucleosynthesis/IvM4gbKH">original creation</a> of <a href="/facts/Hydrogen/BoYHjl0J">hydrogen</a>, <a href="/facts/Helium/yRul93TG">helium</a> and <a href="/facts/Lithium/7vXX6BWA">lithium</a> during the <a href="/facts/Big_Bang/I5T1vTnv">Big Bang</a>. As a <a href="/facts/Predictive_power/SBBA4w4s">predictive theory</a>, it yields accurate estimates of the <a href="/facts/Abundance_of_the_chemical_elements/CE9WehBl">observed abundances</a> of the elements. It explains why the observed abundances of elements change over time and why some elements and their <a href="/facts/Isotope/KD9B1y6o">isotopes</a> are much more abundant than others. The theory was initially proposed by <a href="/facts/Fred_Hoyle/tXjJ0Lbd">Fred Hoyle</a> in 1946, who later refined it in 1954. Further advances were made, especially to nucleosynthesis by <a href="/facts/Neutron_capture/elsFpM12">neutron capture</a> of the elements heavier than <a href="/facts/Iron/QK1JYy8E">iron</a>, by <a href="/facts/Margaret_Burbidge/ImYCgrBj">Margaret</a> and <a href="/facts/Geoffrey_Burbidge/fyrpPhJh">Geoffrey Burbidge</a>, <a href="/facts/William_Alfred_Fowler/WowQ2AlE">William Alfred Fowler</a> and <a href="/facts/Fred_Hoyle/tXjJ0Lbd">Fred Hoyle</a> in their famous 1957 <a href="/facts/B2FH_paper/MM1X74bh">B2FH paper</a>, which became one of the most heavily cited papers in astrophysics history.
<a href="/facts/Stellar_evolution/Qa4vAGmn">Stars evolve</a> because of changes in their composition (the abundance of their constituent elements) over their lifespans, first by <a href="/facts/Hydrogen_burning/qEQJdJe6">burning hydrogen</a> (<a href="/facts/Main_sequence/DJ3Wq8kd">main sequence</a> star), then <a href="/facts/Helium_burning/wV6lacSF">helium</a> (<a href="/facts/Horizontal_branch/SGIJct8A">horizontal branch</a> star), and progressively burning <a href="/facts/Triple-alpha_process/wV6lacSF">higher elements</a>. However, this does not by itself significantly alter the abundances of elements in the universe as the elements are contained within the star. Later in its life, a low-mass star will slowly eject its atmosphere via <a href="/facts/Stellar_wind/bn5J6vpx">stellar wind</a>, forming a <a href="/facts/Planetary_nebula/5Vy84cPq">planetary nebula</a>, while a higher–mass star will eject mass via a sudden catastrophic event called a <a href="/facts/Supernova/Pfo2J23l">supernova</a>. The term <a href="/facts/Supernova_nucleosynthesis/rbzAja5z">supernova nucleosynthesis</a> is used to describe the creation of elements during the explosion of a massive star or <a href="/facts/White_dwarf/gIYlTtrC">white dwarf</a>.
The advanced sequence of burning fuels is driven by <a href="/facts/Gravitational_collapse/7f4zQs8Y">gravitational collapse</a> and its associated heating, resulting in the subsequent burning of <a href="/facts/Carbon_burning/MbHbTB03">carbon</a>, <a href="/facts/Oxygen-burning_process/o1uGg3kL">oxygen</a> and <a href="/facts/Silicon_burning/qpYtHo8c">silicon</a>. However, most of the nucleosynthesis in the mass range <a href="/facts/Mass_number/VyBbJ1oI">A</a> = 28–56 (from silicon to nickel) is actually caused by the upper layers of the star <a href="/facts/Supernova/Pfo2J23l">collapsing onto the core</a>, creating a compressional <a href="/facts/Shock_wave/CqrG1Xm5">shock wave</a> rebounding outward. The shock front briefly raises temperatures by roughly 50%, thereby causing furious burning for about a second. This final burning in massive stars, called explosive nucleosynthesis or <a href="/facts/Supernova_nucleosynthesis/rbzAja5z">supernova nucleosynthesis</a>, is the final epoch of stellar nucleosynthesis.
A stimulus to the development of the theory of nucleosynthesis was the discovery of variations in the <a href="/facts/Abundance_of_the_chemical_elements/CE9WehBl">abundances of elements found in the universe</a>. The need for a physical description was already inspired by the relative abundances of the chemical elements in the <a href="/facts/Solar_System/QIcLSazQ">Solar System</a>. Those abundances, when plotted on a graph as a function of the atomic number of the element, have a jagged sawtooth shape that varies by factors of tens of millions (see <a href="/facts/History_of_nucleosynthesis_theory/F9MIeADF">history of nucleosynthesis theory</a>). This suggested a natural process that is not random. A second stimulus to understanding the processes of stellar nucleosynthesis occurred during the 20th century, when it was realized that the <a href="/facts/Energy/wd8PrQM7">energy</a> released from nuclear fusion reactions accounted for the longevity of the <a href="/facts/Sun/CadPCVHh">Sun</a> as a source of heat and light.

Stellar nucleosynthesis open-in-new

Stellar nucleosynthesis