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we are stardust
hydrogen and neutrons
a few microseconds after the Big Bang, our universe had cooled and expanded enough for all of the quarks to condense into baryons, that is protons and neutrons. Protons are the nucleus of the first element hydrogen, so the Periodic Table consisted of one element for several minutes.
During the first second, there was so much radiant energy in the universe that protons could eject a positron and form a neutron, even though the neutron rest mass was slightly greater than the proton's. There were equal numbers of protons and neutrons until the universe cooled enough that neutrons could decay into protons and electrons, but protons were not energetic enough to form neutrons.
After a few minutes the universe was cool enough that protons and neutrons could fuse into deuterium, tritium, helium 3, and the common helium 4 nuclei, and a trace of the third element lithium. Since free neutrons decay with a half life of about ten minutes, these larger nuclei could form for about 15 minutes. The free neutrons decayed and the universe cooled to the point that the primordial Big Bang nucleosynthesis ceased. Any remaining free neutrons decayed into protons and electrons.
Nucleosynthesis stopped in the universe for perhaps 100 million years until the interstellar medium cooled enough to form the first stars. The first stars were massive because the interstellar medium could not cool enough to form smaller stars.
The first generation of stars were massive and lived fast and died young. In other words, they fused numerous elements, exploded as they died, and dispersed their elements, thereby enriching the interstellar medium from which the next generation of stars condensed. All of the oxygen in the universe was formed in massive stars that went supernova as they died.
carbon and nitrogen
magnesium and silicon
TBD additional text
sulfur and phosphorus
iron and nickel
silver and gold
thorium and uranium
universe 8 billion years after Big Bang
After eight billion years, enough low mass stars died and white dwarfs exploded to produce the current mix of elements found today. Enrichment of interstellar space continues as new stars are born and die, but the general characteristics are the same.
Big Bang nucleosynthesis
Big Bang nucleosynthesis happened in a matter of minutes while free neutrons were still abundant in the early universe. Neutrons are electrically neutral and are not repelled by positively charged protons, so they can get close enough to fuse. Free neutrons are also generated by merging neutron stars, so they formation of the heaviest elements can also occur rapidly.
This is very different from stellar fusion which takes millions or billions of years because most stars do not have free neutrons and very few protons are energetic enough to overcome their coulombic repulsion. In fact protons only fuse due to quantum tunneling, which allows them to violate energy conservation briefly until they pay it back by forming a lower energy bound state. When protons fuse, some of their energy is used to transform some of them to the more massive neutrons that are found in all nuclei other than hydrogen. This process is illustrated in the animations shown below.
Our NetLogo model illustrates the processes without any physics or time scales
Stellar thermonuclear fusion releases energy when nuclei fuse at extreme densities and temperatures. Nucleosynthesis of protons produces a series of increasingly massive nuclei. The process is very rare and slow for any individual particle, but the extreme mass of a star provides an environment in which massive amounts of energy can be released for billions of years.
The fusionHe101 NetLogo model simulates the three steps of fusion that convert hydrogen nuclei into helium 4 nuclei in the interior of the Sun or a Sun-like star. First two protons fuse to form a hydrogen isotope called a deuteron or deuterium nucleus consisting of one proton and one neutron. Second, a proton fuses with a deuteron to form a helium 3 nucleus consisting of two protons and one neutron. Third two helium 3 nuclei fuse to form the more common isotope, the helium 4 nucleus consisting of two protons and two neutrons with the release of the two extra protons. The number of nuclei decreases in the first two steps and increases in the third step, but the number of nucleons does not change because any proton that is lost is transformed into a neutron.
The three steps are:
1 - H1 + H1 → H2 + e+ + nu and e+ + e- → photon + photon
2 - H1 + H2 → He3 + photon
3 - He3 + He3 → He4 + H1 + H1
The first step is very difficult and rate which is why thermonuclear fusion of hydrogen to helium continues for about ten billion years while the Sun is on the main sequence. The first step also releases a neutrino which is non-interacting and quickly escapes the Sun at the speed of light, carrying off a small amount of energy. This step also creates a positron or anti-electron which carries the positive charge lost when one of the protons turns into a neutron. The positron quickly annihilates itself and an electron, converting their masses into electromagnetic energy via a pair of gamma rays. These photons do not travel far before being absorbed by electrons that disperse the resulting thermal energy to other particles through collisions.
The second step only takes millions of years. This process also releases energy in the form of a photon which is also quickly absorbed by an electron.
Our model has many simplifications compared to the 18000 line Fortran solar evolution model that Dr. Joyce Guzik of Los Alamos National Lab gave us in 2006. The large code provides detailed numerical properties throughout the interior of the Sun, but does not provide an easy visualization of the actual processes. Our model is much simpler and does not provide thermal properties or predictions of rates of reactions, but does help the user visualize the processes and think more deeply about what is going on in the core of the Sun.
Sun fusion slides explains in simplified terms how thermonuclear fusion in the core of the Sun converts hydrogen to helium using PowerPoint animation. This sequence of interactions is the basis of the NetLogo fusion model shown above.
four embedded videos on the origin of the elements
"We are made of star stuff": The Origin of the Elements (Part 1 of 2)
The origin of the chemical elementsUniversetsUdvikling2016
The Origin of the Elements