system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why is the production of iron atoms a sign that a star is dying?

If I’m not mistaken, most elements were forged in the cores of stars at the beginning of the universe. Supposedly, when a star starts making iron atoms, that means it’s dying. Why is that?
gpt
A star is big and shines bright. Most stars have hydrogen, element #1. Stars are so big and strong that they can squeeze four hydrogen atoms together to make element #2: helium. When stars fuse atoms together, usually it releases energy that makes the star shine bright. The star keeps doing this and they can make all sorts of elements, including #26: iron. But that takes a lot of energy. When a star makes iron, it uses more energy to make iron than iron makes the star shine. Making iron makes the star tired, and it will die for it. Edit: a star is big and shines bright.