Cosmic Alchemy
Every atom of carbon in your body was forged inside a star. Stellar nucleosynthesis — the creation of elements through nuclear fusion — is responsible for nearly all elements heavier than helium. From the pp-chain that powers our Sun to the explosive silicon burning in supernovae, stars are the foundries of the periodic table. This simulation traces each fusion stage in a massive star, from hydrogen to iron.
The Burning Stages
Massive stars (> 8 M☉) progress through six major fusion stages: hydrogen, helium (triple-alpha), carbon, neon (photodisintegration), oxygen, and silicon burning. Each stage ignites at a higher temperature and completes faster than the last. Hydrogen burning lasts millions of years; silicon burning completes in about one day. The star develops an onion-shell structure with progressively heavier elements toward the center.
The Iron Ceiling
Iron-56 sits at the peak of the nuclear binding energy curve — the most tightly bound nucleus. Fusing iron requires energy rather than releasing it, so when an iron core accumulates to about 1.4 M☉ (the Chandrasekhar mass), electron degeneracy pressure fails. The core collapses in milliseconds, triggering a core-collapse supernova that disperses the newly synthesized elements into the interstellar medium.
Enriching the Universe
Each generation of stars enriches the interstellar medium with heavier elements, increasing the metallicity of subsequent stellar generations. The Sun, a third-generation star, inherited its carbon, oxygen, silicon, and iron from supernovae that exploded billions of years before the solar system formed. Without nucleosynthesis, the universe would contain only hydrogen, helium, and trace lithium — no planets, no chemistry, no life.