Why is the fusion of iron in a massive star's core catastrophic?
Answer
Fusing iron consumes energy rather than releasing it
In stars significantly more massive than the Sun, nucleosynthesis continues through progressively heavier elements in the core until iron is formed. Iron represents the crucial turning point because, unlike the fusion of lighter elements which releases energy, the process of fusing iron actually absorbs or consumes energy. This sudden removal of the primary source of internal thermal support causes the star to lose its outward pressure immediately. This loss of pressure results in a catastrophic and instantaneous gravitational collapse, which subsequently leads to a massive rebound explosion known as a supernova.
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