Higher Tier: Why Iron Ends Stellar Fusion
Part of Life Cycle of Stars — GCSE Physics
This higher tier covers Higher Tier: Why Iron Ends Stellar Fusion within Life Cycle of Stars for GCSE Physics. Revise Life Cycle of Stars in Space Physics for GCSE Physics with 13 exam-style questions and 12 flashcards. This topic appears regularly enough that it should still be part of a steady revision cycle. It is section 11 of 14 in this topic. This section is most useful once the core foundation idea is secure, because it adds the detail that pushes answers higher.
Topic position
Section 11 of 14
Practice
13 questions
Recall
12 flashcards
🎓 Higher Tier: Why Iron Ends Stellar Fusion
Nuclear fusion releases energy when lighter nuclei combine to form a heavier, more stable nucleus. The energy released comes from the difference in nuclear binding energy — the energy required to hold the nucleus together.
Iron-56 has the highest nuclear binding energy per nucleon of any element. This means it is the most stable nucleus. Fusing iron nuclei together does not release energy — it actually requires energy input. So when a massive star's core fills with iron, fusion cannot proceed further, and there is no longer an energy source to provide outward radiation pressure. The core collapses suddenly under gravity, triggering the supernova.
This explains why the sequence of fusion in massive stars stops at iron: H → He → C → Ne → O → Si → Fe, and then nothing — catastrophic collapse.