🔭 How the Sun Shines: The Nuclear Reactions

The Sun is very hot and very dense so these protons collide.
But this doesn't cause a nuclear reaction because there's no neutrons.
Most of the time when two protons collide they immediately fly apart producing no energy.
But it is possible, very very rarely, that something else happens: beta decay.
At the moment the two protons collide, one of them undergoes beta decay and turns into a neutron.
This gives us Hydrogen-2 and releases tons of energy. The Hydrogen-2 nucleus continues moving around and when it bumps into a proton it turns into Helium-3 and this releases tons of energy..
As this process continues, the Sun produces more and more Helium-3.
When two Helium-3 nuclei collide, they can form into an even better combination Helium-4 and this releases tons of energy.