Which element's core formation signals the absolute end of energy generation via fusion in massive stars?
Answer
Iron.
The evolutionary track of a very massive star involves sequentially fusing heavier and heavier elements in nested shells within its core—starting with hydrogen, moving to helium, then carbon, neon, and so on. This process of building heavier elements releases the necessary energy to oppose gravity. However, this chain terminates abruptly upon the creation of an iron core. Fusing iron atoms does not release energy; rather, it consumes energy (requires an input of energy) to proceed. Once the core becomes iron, the star's primary energy source vanishes instantly. With no outward thermal pressure being generated, gravity immediately overcomes all remaining forces, leading to catastrophic core collapse and the violent death explosion.
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