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by pdonis 19 days ago
> If you think about it, they must have a lot of protons to generate a field so strong

Not necessarily. Neutrons have a magnetic moment. As I understand it, there is a magnetohydrodynamic model of how a magnetar's field gets generated, which would require protons, but it's not the only model and we don't have enough data to be able to rule out other models.
2 comments
robocat 19 days ago
Aside: Carbon-13 has one more neutron than Carbon-12, so the unpaired neutron gives it a magnetic moment which is what is used for C13 Nuclear Magnetic Resonance (NMR) spectroscopy.

https://en.wikipedia.org/wiki/Carbon-13_nuclear_magnetic_res...

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taneq 18 days ago
> Neutrons have a magnetic moment.

Wait, what? Huh, I have some reading to do. Thanks! :D

I thought neutron stars generally had a shell or crust of iron, which generates a magnetic field (as metals do) if the neutron star is spinning.

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pdonis 17 days ago
> I thought neutron stars generally had a shell or crust of iron, which generates a magnetic field (as metals do) if the neutron star is spinning.

They do, but the neutrons themselves also have magnetic properties. (The simplest heuristic way to think of it is that neutrons are made of three quarks, and the magnetic moment is due to the quarks moving around inside the neutron. But that's a highly heuristic picture and leaves out a lot of complications.)

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