Hydrogen fusion: the proton-proton chain and the CNO cycle

Assembled from 30 blocks · 2 evidence · 30 related

1. Story
2. The two routes by which four protons become one helium-4 nucleus. The proton-proton chain begins with two protons fusing to deuterium via the weak interaction - an extraordinarily slow step, which is why the Sun burns for billions of years rather than detonating. The CNO cycle uses pre-existing carbon, nitrogen and oxygen as catalysts, consuming and regenerating them, and is far more temperature-sensitive, so it takes over in hotter cores. In the present-day Sun about 98.5 per cent of the energy comes from the pp chain and about 1.5 per cent from CNO; theoretical models put the crossover at roughly 1.3 solar masses. Either way about 0.7 per cent of the rest mass of the participating hydrogen is converted to energy, most of it as photons that take a very long time to random-walk out, and a small fraction as neutrinos that leave immediately and carry direct information about the core. Not a place.
3. Knowledge
4. Main sequence (core hydrogen burning)
5. Hydrogen fusion: the proton-proton chain and the CNO cycle
6. Stellar nucleosynthesis
7. Connections
8. Initial stellar mass
9. Main sequence (core hydrogen burning)
10. Stellar nucleosynthesis
11. The Sun
12. Payne concludes that stars are mostly hydrogen - and disclaims it
13. Neutrinos from the solar CNO cycle are detected
14. Initial stellar mass
15. Protostar
16. Red giant and asymptotic giant branch
17. Hydrogen fusion: the proton-proton chain and the CNO cycle
18. The Sun
19. Hertzsprung-Russell diagram
20. The Sun forms and settles onto the main sequence
21. Hertzsprung and Russell independently plot luminosity against temperature
22. Hydrogen fusion: the proton-proton chain and the CNO cycle
23. The iron peak in nuclear binding energy
24. Rapid neutron capture (the r-process)
25. The first stars form from metal-free gas
26. B2FH sets out the synthesis of the elements in stars
27. A neutron-star merger is detected in gravitational waves and light
28. Evidence
29. Reports the first direct detection of solar neutrinos from the CNO cycle. Title and DOI were read from the publisher listing via search; the paper was not fetched, and the quoted ~1 per cent CNO share of solar energy output comes from accompanying institutional summaries rather than the paper.
30. Supports general stellar-physics statements in this pack: mass-luminosity scaling, main-sequence lifetimes, degeneracy support and the conventional 1.4 solar mass Chandrasekhar value. This is university-maintained educational reference material, not primary literature, and it was read via search summary rather than fetched. Primary citations should replace it for any figure a reader might quote.