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Fusion in stars
Intermediate
Proton–proton chain powers the Sun.
In the Sun, the proton–proton chain converts 4 protons into helium-4, releasing 26.7 MeV, at about 15 million K. Heavier stars use the CNO cycle.
The Sun fuses 600 million tonnes of hydrogen each second.
Takes billions of years because the first step is a weak interaction.
In more detail
Stars fuse hydrogen into helium in their cores, releasing energy that balances gravity. Heavier stars can fuse heavier elements, up to iron.
Real-world uses
- Stellar fusion produces the energy we receive from the Sun.
- Stellar nucleosynthesis creates the elements in the universe.
- Astronomers explain why the Sun shines by describing how hydrogen fuses into helium in its core.
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Frequently asked questions
How does the Sun fuse hydrogen?
Through the proton-proton chain, or the CNO cycle in heavier stars.
Why does the Sun shine steadily?
Because fusion rate adjusts to balance gravity, maintaining stable pressure.
How does the Sun fuse hydrogen?
Through the proton–proton chain, in which hydrogen nuclei combine step by step to form helium-4.
Related topics in Atomic & Nuclear Physics
Nuclear reactors · Nuclear weapons · Nuclear fusion · Fusion reactors · Neutron discovery · Neutrinos