Stellar nucleosynthesis helium
Elements formed in stars
Fowler, T. 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. Despite the name, stars on a blue loop from the red giant branch are typically not blue in color, but are rather yellow giants, possibly Cepheid variables. Timeline[ edit ] Periodic table showing the origin of each element. The subsequent nucleosynthesis of the heavier elements requires the extreme temperatures and pressures found within stars and supernovas. If the star is massive enough this rises the temperature to a level where C12 - C12 collisions start producing heavier elements such as Mg24, and O16 - O16 collisions producing S Burbidge, G. Calcium plus helium produces titanium. However, the real credit for developing it into a coherent theory is given to Fred Hoyle's work in the aftermath of World War II. Physicist Lawrence Krauss notes that it takes , years for the carbon to burn into oxygen, 10, years for the oxygen to burn into silicon, and one day for the silicon to burn into iron and herald the collapse of the star. 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. 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.
The majority of these occur 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.
The alpha process then combines helium with carbon to produce heavier elements, but only those with an even number of protons.
Each atom is rearranged or re-used. Elements beyond iron are made in large stars with slow neutron capture s-process. Reaction rate[ edit ] The reaction rate per volume between species A and B, having number densities nA,B is given by: r.
This temperature is achieved in the cores of main sequence stars with at least 1. However, a massive star reaches the stage of Iron synthesis and ends up with an Iron core. It takes nearly 10 million years to burn through the hydrogen and then things heat up and the helium begins fusing.
Elements from carbon up to sulfur may be made in small stars by the alpha process.
However, the real credit for developing it into a coherent theory is given to Fred Hoyle's work in the aftermath of World War II. It is also called "hydrogen burning", which should not be confused with the chemical combustion of hydrogen in an oxidizing atmosphere.
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. See my copyright notice for fair use practices.
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