How do the fusion reactions in the sun compare to the fusion occurring in larger stars and supernovas?

1 Answer
Dec 13, 2016

Different fusion reactions occur in small stars, large stars and supernovae.


In a smaller star such as the Sun the main process of fusion from Hydrogen to Helium is the proton-proton chain reaction. This is where two protons combine under the strong nuclear force to form a diproton.

#""_1^1H + ""_1^1H -> ""_2^2He + gamma#

The Helium 2 or diproton is very unstable and usually breaks down into two protons. Occasionally transforms into deuterium by the weak nuclear force.

#""_2^2He -> ""_1^2H + e^+ + nu_e#

Then a proton is added to form Helium 3.

#""_1^2H + ""_1^1H -> ""_2^3He + gamma#

There are several reactions which depend on the temperature of the star which lead to the most stable #""_2^4He#.

Larger stars use the CNO fusion reactions. This creates Helium from Hydrogen by a fusion process converting Carbon to Nitrogen to Oxygen and back to carbon. There are several reactions.

#""_6^12C + ""_1^1H -> ""_7^13N + gamma#
#""_7^13N -> ""_6^13C + e^+ + nu_e#
#""_6^13C + ""_1^1H -> ""_7^14N + gamma#
#""_7^14N + ""_1^1H -> ""_8^15O + gamma#
#""_8^15O -> ""_7^15N + e^+ + nu_e#
#""_7^15N + ""_1^1H -> ""_6^12C + ""_2^4He#

In the case of supernova explosions, vast quantities of free neutrons are released when the core collapses. A process called neutron capture creates elements heavier than Iron. Many elements heavier athan Iron and up to Plutonium are created in this way.