Define Nucleosynthesis

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Stars like the sun Details were discussed in the section on Fusion.

In astronomy – and astrophysics and cosmology – there are two main kinds of nucleosynthesis, Big Bang nucleosynthesis (BBN), and stellar nucleosynthesis.

triple alpha, s process, proton-proton chain, CNO cycle), but the end result is the fusion of hydrogen (and helium) to produce carbon, nitrogen, oxygen, … In the red giant phase of a star’s life, much of this matter ends up in the interstellar medium … There are other ways new nuclei can be created, in the universe (other than BBN and stellar nucleosynthesis); for example, when a high energy particle (a cosmic ray) collides with a nucleus in the interstellar medium (or the Earth’s atmosphere), it breaks it into two or more pieces (this process is called cosmic ray spallation).

This produces most of the lithium (apart from the BBN Li), beryllium, and boron.

In the amazingly successful set of theories which are popularly called the Big Bang theory, the early universe was very dense, and very hot.

As it expanded, it cooled, and the quark-gluon plasma ‘froze’ into neutrons and protons (and other hadrons, but their role in BBN was marginal), which interacted furiously … The universe continued to cool, and soon became too cold for any further nuclear reactions …

Almost all the hydrogen and helium present in the universe today (and some of the lithium) were created in the first three minutes after the big bang. There are no stable isotopes (of any element) having atomic masses 5 or 8. The triple-alpha process is not relevant in main sequence (normal) stars like the sun because their core temperatures are too low.

All of the other naturally occurring elements were created in stars. You need really massive stars for this — say 20 to 120 times the mass of the sun.

Heavier elements are created in different types of stars as they die or explode.

The idea that stars fuse together the atoms of light elements was first proposed in the 1920s, by Einstein's strong supporter Arthur Eddington.


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