I get they need more energy than a “regular” star can provide, up to iron. That two stars colliding can provide the energy. And more neutrons in the nucleus offset the protons repelling each other.
No s-capture or whatever language please, I’m looking for small words & drawings w/ crayons.
How do heavy elements form beyond iron, why is it so hard to make the packing of protons/neutrons so hard? What role do electrons play, aside from the negative charge for protons (if any)?
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Fusion of elements heavier than lead consumes energy, but stars are producing a lot of energy from fusing lighter elements so there’s ample energy to create heavier elements until the lighter elements start running out.
So elements other than hydrogen are generally created by smashing lighter elements together, known as nuclear fusion. Smashing hydrogen into hydrogen creates helium, for instance. This smashing is done by putting them under a lot of pressure and heat.
When this happens with lighter elements, those lighter than iron, smashing them together this way creates energy. As the combining elements get heavier, this becomes harder and harder and generates less energy.
When you reach iron, the situation reverses. The energy needed to crush elements together to make new elements heavier than iron takes more energy than you get out of it. The pressure and heat required exceeds that in the core of a star under normal circumstances.
So in order to create this incredible heat and pressure, you need something really really violent, something that makes the normal inside of a star seem cool and comfy by comparison.
Until recently, we thought that the only way this happened was during a supernova. Now we have realized that colliding white dwarfs and neutron stars are probably necessary for the very heaviest elements due to the enormous pressures and temperatures required.
>I get they need more energy than a “regular” star can provide, up to iron.
It’s not quite like that. It’s not that they need *more* energy, it’s that they need energy and don’t release any. A star could theoretically keep fusion going indefinitely otherwise, they absolutely have the conditions to enable that.
So no elements heavier than iron are made during a star’s life, period. Iron is fusion poison. In fact, producing iron is what causes the spectacular Type II (core collapse) supernovas.
This collapse is what forces the production a lot of heavy elements, either directly or by decay of even heavier elements which were forcefully fused.
But even they don’t produce MOST of the heavy elements in the universe. That honour goes to colliding neutron stars. When they do, they can rip eachother apart.
As the name suggests, they’re made (almost) entirely of neutrons. But to keep that way, they require the unreal levels of pressure caused by their gravity. Once a clump of neutron matter is released, it will immediately revert to a more energetically favourable setup, i.e. regular proton/neutron matter.
So some of the neutrons decay into protons and electrons. And then the new absurdly large nucleus breaks apart into smaller and smaller chunks, passing through the really radioactive elements that decay in milliseconds down to the ones with enough stability to survive until today. And that’s how we get the majority of elements heavier than iron.
As for why protons and neutrons like to coexist, it’s a combination of two things:
Neutrons are unstable on their own and decay, but can exist bound to protons. It’s just how it works.
Protons can happily exist alone, see hydrogen, but have a limit to how many can be packed into a nucleus due to electrostatic repulsion. They’re all positively charged. But having neutrons in the mix allows a bit of separation, allowing the stronger Strong Force to still hold.
But at some point you reach a point where there are too many neutrons trying to keep the protons bound, and they become unstable again. And they decay. And suddenly electrostatic repulsion gets a boost, and the nucleus cracks.
There are soecific combinations of protons and neutrons that are more stable than others, and again that’s just quantum physics, but it’s kind of like atoms and ions, it’s all about binding energies etc.
Electrons are just electrons, but they can combine with a proton into a neutron and vice-versa.
Well, you gave the answer yourself. Through neutron star collisions. They have enough energy to overcome electron degeneracy. You might ask how, given that such fusions don’t release net energy. You’re right, they don’t. But neutron star collisions are one-time events, they don’t need to sustain a positive fusion pressure like stars do.
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