An iron core is actually the precursor for either a black hole or a neutron star.

There is an exothermic fusion chain of elements that are burned in stars, the last stage of which is silicon, that ends with iron.

https://en.m.wikipedia.org/wiki/Silicon-burning_process

At iron, no further exothermic fusion is possible, so the core is no longer able to resist the pressure of collapse.

The iron atomic nuclei themselves break down, the protons combine with electrons to form neutrons where they are able, and if the total mass is below the Tolman–Oppenheimer–Volkoff, then neutron degeneracy pressure is able to stop the collapse, otherwise a black hole forms.

https://en.m.wikipedia.org/wiki/Tolman%E2%80%93Oppenheimer%E...

A star needs to be 8 solar masses for this to happen. Our sun ends at carbon.