Once a very large star starts to create iron it is using up more energy than it produces this results in the star cooling and collapsing in on itself this collapse result in a rebound effect known as a supernova which scatters all the heavier elements created in the final moments before the supernova. https://youtu.be/w1GlDVt1Mpk
This is why rocky planets and life itself are referred to as star dust we literally are, no supernovas and none of us would exist.
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