Formation of Elements in the Universe

Study Notes

The origin of all naturally occurring elements involves two phases:
- Primordial nucleosynthesis (Big Bang)
- Stellar nucleosynthesis

The Big Bang created the "light" elements (hydrogen, helium, trace lithium and beryllium)
These elements formed within the first few minutes after the Big Bang, during a period of extremely high temperature and density
A rapidly cooling cosmos allowed quarks to clump into protons and neutrons
Electrons combined with these particles to create light atoms, mainly hydrogen and helium

Stars produce heavier elements via nuclear fusion
The density inside a star is large enough to sustain fusion for extended periods
Stellar nucleosynthesis produces elements heavier than helium such as carbon, nitrogen, oxygen, silicon, and iron
Multiple nuclear fusion mechanisms drive this process, including proton-proton chain, the carbon-nitrogen cycle and triple alpha process
Stars with high temperatures near their cores create heavier elements like silicon and iron

Elements heavier than iron are formed through neutron capture reactions in supernovae
Supernovae are explosions of massive stars where neutrons are added to existing atomic nuclei
Another way elements heavier than iron form is via fusion reactions in the interior of stars, although tremendous amounts of energy are required for the reaction to occur

Isotopes are forms of an element with the same atomic number but different atomic masses (or mass numbers)
They have the same number of protons, but different numbers of neutrons
Examples include protium, deuterium and tritium which are all isotopes of hydrogen
Carbon also has isotopes such as Carbon-12 and Carbon-14

The elements are formed through nuclear fusion reactions in stars and explosions of massive stars
The reactions create a wide range of elements and isotopes.
Nuclear reactions and interactions have created the elements we have today