One “wow” moment that blew me away during my grad physics studies was the realisation that a neutron star is effectively one gigantic atomic nucleus.
Neutron stars are held together by gravity, not nuclear forces. Also, the mix of particles is very different from an actual nucleus. The physics are pretty different.
It's a bit like saying the SpaceX Starship, and my mechanical pencil are the same thing, because they have the overall same shape, and are made of stainless steel.
Neutron stars are governed by both gravitational and the strong force. [edited]
Quite different from ealier phases of stars which are held together by gravity.
> Also, the mix of particles is very different from an actual nucleus.
Which particles? The key difference vs an atomic nucleus other than the immense size is that the neutron star is not charged like an atomic nucleus, as most of the precursor star’s protons and electrons have fused into neutrons.
> In popular scientific writing, neutron stars are therefore sometimes described as "giant nuclei". However, in other respects, neutron stars and atomic nuclei are quite different. A nucleus is held together by the strong interaction, whereas a neutron star is held together by gravity. The density of a nucleus is uniform, while neutron stars are predicted to consist of multiple layers with varying compositions and densities.
It's just a pop-sci meme.
As for the structure, see here:
I’ll only comment on one part of the Wikipedia quote regarding constant densities of atomic nuclei.
The neutron star will have a constant density on any length scale as large as an atomic nucleus. The layered structure manifests over length scales of kilometers, which is 10^18 times larger than an atomic nucleus.
Nobody who actually works in fields related to nuclear physics or astrophysics considers a neutron star as being "just a giant nucleus", no matter how often that image may be used in pop-sci articles and youtube videos.
More linky stuff, again related to your statement that neutron stars are held together by the nuclear force (which is false):
https://www.nuclear-power.com/nuclear-power/reactor-physics/...
> Since they have some similar properties as atomic nuclei, neutron stars are sometimes described as giant nuclei. But be careful, neutron stars and atomic nuclei are held together by different forces. A nucleus is held together by the strong force, while a neutron star is held together by gravitational force.
At the core, a neutron star is likely very nearly pure neutronium, as other particles simply won't exist long under the conditions present.
As depth decreases, other particles can exist, and at the surface there are likely free nuclei and atoms of elements, though my probably with low nuclear potential. Fission and fusion would be accelerated by the energies involved.
That's a lay reading / bits of stray collected memories, though quick checking seems to confirm most of this. See:
https://heasarc.gsfc.nasa.gov/docs/objects/binaries/neutron_...