Nucleosynthesis | Wikipedia audio article
Channel: wikipedia tts
Date: 08/12/2018

This is an audio version of the Wikipedia Article:
Nucleosynthesis


00:03:30 1 Timeline
00:05:55 2 History of nucleosynthesis theory
00:09:50 3 Processes
00:10:57 4 The major types of nucleosynthesis
00:11:08 4.1 Big Bang nucleosynthesis
00:12:18 4.2 Stellar nucleosynthesis
00:14:58 4.3 Explosive nucleosynthesis
00:19:56 4.4 Neutron star collision
00:20:44 4.5 Black hole accretion disk nucleosynthesis
00:20:59 4.6 Cosmic ray spallation
00:22:09 5 Empirical evidence
00:22:40 6 Minor mechanisms and processes
00:25:57 7 See also



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SUMMARY
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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. Seventeen minutes later the universe had cooled to a point at which these processes ended, so only the fastest and simplest reactions occurred, leaving our universe containing about 75% hydrogen, 24% helium, and traces of other elements such as lithium and the hydrogen isotope deuterium. The universe still has approximately the same composition today.
Heavier nuclei were created from these, by several processes. Stars formed, and began to fuse light elements to heavier ones in their cores, giving off energy in the process, known as stellar nucleosynthesis. Fusion processes create many of the lighter elements up to and including iron and nickel, and these elements are ejected into space (the interstellar medium) when smaller stars shed their outer envelopes and become smaller stars known as white dwarfs. The remains of their ejected mass form the planetary nebulae observable throughout our galaxy.
Supernova nucleosynthesis within exploding stars by fusing carbon and oxygen is responsible for the abundances of elements between magnesium (atomic number 12) and nickel (atomic number 28). Supernova nucleosynthesis is also thought to be responsible for the creation of rarer elements heavier than iron and nickel, in the last few seconds of a type II supernova event. The synthesis of these heavier elements absorbs energy (endothermic process) as they are created, from the energy produced during the supernova explosion. Some of those elements are created from the absorption of multiple neutrons (the R process) in the period of a few seconds during the explosion. The elements formed in supernovas include the heaviest elements known, such as the long-lived elements uranium and thorium.
Neutron star mergers and collisions are also responsible for many heavy elements, via the r-process ("r" stands for "rapid"). Neutron stars are extremely dense remnants of supernovae, and as their name suggests, they consist of a complex state of matter, predominantly made of tightly packed neutrons. When two such dense stars collide, a large amount of neutron-rich matter may be ejected at extremely high temperatures and under exotic conditions, and heavy elements may form as the ejecta begins to cool. In 2017, the merger of GW170817 led to the detection of substantial signatures of gold, platinum and other heavy elements over an extended period.
Cosmic ray spallation, caused when cosmic rays impact the interstellar medium and fragment larger atomic species, is a significant source of the lighter nuclei, particularly 3He, 9Be and 10,11B, that are not created by stellar nucleosynthesis.
In addition to the fusion processes responsible for the growing abundances of elements in the universe, a few minor natural processes continue to produce very small numbers of new nuclides on Earth. These nuclides contribute little to their abundances, but may account for the presence of specific new nuclei. These nuclides are produced via radiogenesis (decay) of long-lived, heavy, primordial radionuclides such as uranium and thorium. Cosmic ray bombardment of elements on Earth also contribute to the presence of rare, short-lived atomic species called cosmogenic nuclides.