Title pretty explanatory, but I tried to google it and the only thing I can get is the ai telling me it “mainly forms in supernovae” but what i want to know if how the rest of it forms. I’m not looking for answers to where it is on earth, what forms it can be found in on earth, the fact that meteorites can bring elemental iron to the surface. I want to know specifically how the element is formed in the universe. How does iron exist??? (other than supernovae, because that’s what google says MAINLY it comes from, but I want to know every source)
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Nuclear fusion – atoms combine into heavier and heavier elements. This will happen in stars because a lot of energy (think heat) is required to overcome opposing charges. The fusion itself releases even more energy, hence stars are energy positive.
In the latter stages of a star’s life cycle, you get supernovas, that’s how the elements get distributed to other places.
This image from Wikipedia gives an idea of how different elements form via nucleosynthesis. See also the nucleosynthesis article on Wikipedia.
Iron is the heaviest element that is formed via fusion in the cores of stars. Hydrogen fusion occurs towards the outer shell of the star resulting in Helium, which sinks due to its heavier atomic mass. This process continues fusing heavier and heavier elements until you get an iron core. At some point the star explodes and that iron is distributed in the cloud of debris.
Our solar system is made up from the remnants of previous stars and explosions. Some of the iron from those stars ended up either accreting to the earth when it was still a molten ball or has fallen as meteorites since then. But none of the elemental iron actually formed in our solar system, all of it came from elsewhere
Stars fuse atoms in their cores, yeah? So let’s say it’s fusing Hydrogen. It "smashes" 2 Hydrogen atoms together to produce a Helium atom and a bunch of energy (light). Well what happens when it runs out of Hydrogen to smash together? Lucky for the star, it happens to have a bunch of Helium laying around from all that fusing Hydrogen, so it just starts fusing that together. Rinse and repeat until you get to the heaviest 2 atoms a star can fuse together, which is Silicon. The result is Iron. When this star runs out of atoms to fuse, it loses the fight against gravity and sheds it’s outer core in a supernova explosion. This explosion scatters that Iron out into the Universe.
Also, iron is located at the knee of the binding energy per nucleus curve (https://www.researchgate.net/figure/The-binding-energy-per-nucleon-against-the-nucleon-number-The-fusion-and-fission_fig1_40901505). This means that all elements lighter than iron releases energy when fused, and all heavier elements release energy when split. This explains why both fusion and fission can yield net positive energy. But it also means that iron is sort of the endgame for all nuclear chain reactions as both fission and fusion with iron requires more energy input than it outputs.
This doesn’t explicitly answer your question, but it is an interesting addition to the answers you’ve already received.
Iron-56 (the most common isotope) forms in massive stars during silicon burning where silicon nuclei fuse with helium to form sulfur, then argon, calcium, titanium, chromium, and finaly iron – this happens in the last few days before the star goes supernova bcause iron fusion requires energy rather than releasing it.