I watched the kurzgesagt (https://youtu.be/udFxKZRyQt4) about neutron stars and he explained the inside of the stars are basically just a huge atomic core. But how do we know that? We have a hard time seeing atoms in labs here on Earth, how is it possible to see them light years away?
In: Physics
We don’t know.
Basically, we assume the laws of physics for gravity and quantum physics still apply, and try really hard to figure out some properties.
We think there is a pressure where electron get so compacted that they merge with the protons. We know if that happen that this makes a neutron (as neutron decay into proton+electrons).
We think there is a pressure where neutronium (atoms made exclusively of neutrons) start to pair up, and make di-neutronium soup, because it seems to be slightly more stable than unpaired ones (they don’t like being together, but they take less space so that relieve a little bit of the pressure).
We think there is a pressure where they become pasta (1D chain), then lasagna (2D sheets) and then a core (3D solid), mostly because it looks like 1D neutronium structures are a little bit more stable than 2D neutronium structures which themselves are a little bit more stable than 3D. But at this scale of pressure it’s really speculative.
Below that we have no clue. We don’t know if black holes could spontaneously form then evaporate, or if we can have a weird soup of quarks, or exotic form of matter.
Ideally we would have a record of seismic events at the surface of a neutron star, but that would require direct observation.
Tell it depend on what part you mean exactly, some were observed some are theoratically, meaning it fit with our model of physic and this is what should happen given what we know, but right now we have no way of confirming it.
First we know that the neutron star is made of Iron. Why we know that? Well a supernovea occur because iron accumulate in the core, so if the core is mostly made of something else it couldn’t go supernovea yet. Then we know the mass and dimensions of a neutron star, by looking at it with instrument and how it interact with other stuff. A bit like we measure the mass and dimensions of planets or stars. So now that we know that, we can model the gradiant of pressure along the depth of the star. That pretty much like we can calculate the pressure of water as we go deeper, we can calcualte what will be the pressure at each depth in the star.
Next step is two fold, theorically we can calculate with our current model what should happen to matter at those different pressure and secondly we can test some of it with particule accelerator. By accelerating small particle to extreme speed, we can see what happen to them if they collide, create huge pressure and can see if that fit our model or if there is something we don’t understand.
So if you look at the video, we know that the outer layer is iron, because at this point the pressure is low enough to keep iron intact. But as the pressure get higher, we know that at a certain pressure electrons and protons fuse to get neutrons. So we can calculate at which depth the pressure is enought to do that. I’m not sure if we recreated that in a particle accelerator for sure, but it’s possible since both of those are charged particles. What I know for sure is that this nuclear pasta is purely theoric. It’s the point where the nuclear force and coulomb repulsion are equal so we know that this happen, but what exactly it would be is speculation based on what we know of physics.
We aren’t looking at one atom in a star we are looking at the byproduct of billions of atoms, in addition knowing how atoms operate at various temperatures and pressures enables us to predict what is happening in a star, when those predictions match observations we can be fairly sure what is happening – What happens during the life of a large star. Part 3: Neutron stars, Pulsars and Magnetars
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