system
Given the following post, respond as if you're commenting on Reddit:
human
Why can't stars fuse Iron?
gpt
Well, stars, if they are large enough, CAN fuse iron, as long as it's an iron isotope of 55 or lower. Our star can't fuse iron at all, because it's not big enough either.

The reason is that fusion up until nuclei of 55 protons/neutrons or less will release energy. At nickel and Iron 56 and higher, it TAKES energy to create fusion to higher isotopes. 

This is why Andreas Rossi's claim about the E-cat is wrong because he claims energy release from fusing nickel to copper. That's contrary to the laws of physics as most all supernovae have shown.

This is essentially why giant stars SuperNova. Soon as they've fused up to Iron 56, the nuclear fusion energy processes quickly shut down. The star begins to contract because fusion was keeping it large, it compresses to a very tight size, and then it supernovas!! Spewing out much of its mass in neutrinos, light, & mass ejections to spread newly formed metallic elements upwards of well beyond uranium and Pu to seed the local interstellar region. This will eventually create some metal containing stars (& planets) as children many megayears down the line.

The iron in our hemoglobin and cytochromes, and the Cobalt in our B12 vitamins mostly came from supernovae. We are composed of star stuff, of at least one supernova's matter. & We are here, living right now, reading this because of the fact that Fe-56 can't fuse thus releasing energy. Cool, huh?!!