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The Question

(Submitted January 14, 1998)

If neutron stars consist of only neutrons, how is it possible that they have a magnetic field? I am just a hobbyist, but I thought that the presence of electrons is necessary for a magnetic field.

The Answer

This is a good question. The answer, I think, is that neutron stars are not pure neutrons. If they were, the neutrons would decay. A small (10%) fraction of electrons and protons are present which provide a rate of neutron formation via inverse beta processes which balance the neutron decay. These protons are highly degenerate and superconducting, so the magnetic field is frozen into the neutron star. The origin of the field is probably the parent star, although various schemes have been suggested for generating fields in neutron stars.

I hope this helps,

Tim Kallman
for the Ask an Astrophysicist team

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