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Why neutron stars have magnetic fields, when neutrons have neutral electric charge?
- Marko (age 25)
So far as I can tell from a standard review article ( http://arxiv.org/abs/astro-ph/0307133v1
) the fields come from circulating electrons on the surface. Why are there electrons in a neutron star? The neutrons spontaneously decay into protons and electrons unless they are under high pressure or bound up in stable nuclei. No matter how high the internal pressure of a neutron star, near the surface there has to be a low-pressure crust.
Incidentally, although a neutron has no net charge, it does have some internal structure involving charged quarks. As a result, it can have a magnetic moment. In fact it does, with a moment about 2/3 as large as a proton. However, if I understand the review correctly, this is not a major contributor to the magnetism. One would not expect it to be, since under high pressure the neutrons fill up all the available low-energy states, including both spin states with opposite signs.
(published on 03/03/2011)
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