When the Sun died, the hydrogen in its core would be exhausted, and everything would begin to cool.
The internal thermal pressure would no longer support its structure. Gravity would take over, and its core would continue to collapse.
The collapse would increase the pressure in the Sun's core, causing the gas to expand in an instant and its volume to increase until it became a red giant.
Its radius would extend as far as Earth and swallow this beautiful planet. Compared to the entire universe, the Sun was insignificant. Even observed from outside the Milky Way, it might not be visible at all because it was too small, merely a medium-mass star.
Iron was not rare on Earth. It was even present in everyone's body. It was iron that gave human blood its rusty taste.
Once a red giant formed, as its outer regions rapidly expanded, the helium core contracted inward under the opposing force. The compressed matter grew hotter and hotter, but a star with the Sun's mass could only fuse hydrogen into helium, then helium into carbon before its life ended. The final carbon core would not continue fusing.
More massive stars, after exhausting their hydrogen and helium, could continue burning their carbon cores to produce heavier elements such as sodium and magnesium, all the way up to iron.
Under certain conditions, elements with atomic numbers greater than iron could undergo nuclear fission and ultimately produce iron. Under certain conditions, elements with atomic numbers lower than iron could undergo nuclear fusion and likewise ultimately produce iron.
Iron lay precisely at the threshold between fusion and fission. It could undergo neither fusion nor fission, so in the end, only iron remained.
The iron on Earth and in the human body might have come from a massive star, at