Nucleosynthesis · 4 ¹H → ⁴He
The Proton–Proton Chain
The dominant way low-mass stars like the Sun turn hydrogen into helium: through a chain of steps, four protons are fused into a single helium-4 nucleus, releasing energy and neutrinos. It powers the cores of the coolest main-sequence stars, where temperatures are too low for the competing CNO cycle.
Highlights
- ›How the Sun shines
Stars, stages & concepts
Across stellar astrophysics
Knowledge connections
- Associated withMain-Sequence Evolution
- Associated withThe Sun
- Associated withMain-Sequence Evolution
- Associated withThe CNO Cycle
Sources
The primary and reference sources this topic draws on.
- NASANational Aeronautics and Space Administration
Mission data, planetary science, space telescopes, and public-domain imagery.
Most NASA-produced imagery is in the public domain; individual items are checked for usage terms before publication.