Iron is a starkiller for stars at least 1.5 times larger than our sun. This is science fact, not science fiction.
"In the world of science fiction, there are many ideas about what a starkiller machine might be like. Strangely enough, it's as run-of-the mill as something as iron. To a star, iron is the most dangerous element in the universe. It's poison. Iron absorbs energy. From the moment a massive star creates iron, it has only seconds to live. The star is trying to dump energy into that iron ball and trying to make it fuse, but it can't. And so that ball is robbing the star of energy, and it's that energy that is supporting the star itself. So, as soon as that iron starts to be created ...