What process powers the Sun?

What process powers the Sun? Nuclear fusion powers the Sun. In its extremely hot, dense core, hydrogen nuclei combine through the proton–proton chain, ultimately forming helium and releasing energy.

Four hydrogen nuclei do not simply join in one step. The chain involves several reactions, including the conversion of two protons into neutrons, the production of deuterium and helium-3, and the final formation of helium-4. A tiny fraction of the original mass becomes energy, in accordance with Einstein’s mass–energy equivalence.

The core reaches roughly 15 million kelvin, and immense pressure helps keep the reacting plasma confined by gravity. Quantum tunneling also matters: protons can occasionally pass through the electrical repulsion that would normally prevent positively charged nuclei from coming close enough to fuse.

Fusion energy moves outward through the Sun’s interior before escaping from the photosphere as sunlight and other radiation. Neutrinos created in the reactions travel out almost immediately. The Sun is not burning chemically like wood or fuel; chemical combustion could not supply its power for billions of years. Nor is it undergoing nuclear fission, which splits heavy nuclei rather than joining light ones.