A neutron star is stellar remnant that results from the gravitational collapse of a massive star (between 8 to 20 solar masses). Even though neutron stars are composed of almost entirely neutrons, they have very strong magnetic fields.
To understand why a neutron star has a huge magnetic field, let's look at its structure.
This model hasn't been proven, but it gives very good understanding of neutron stars and reveals many known properties of neutron stars. The surface of a neutron star is composed of ordinary nuclei with a sea of free electrons flowing around them. Most of the nuclei are left over hydrogen, helium and iron. The atmospheres of these stars, according to recent hypothesis, could be at most several micrometers. This is because of the intense gravity on the surface. A calculation of gravity is here. This is approximately 10^12 times stronger than earth's gravity.
A little deeper into the star, the gravity gets strong enough so that neutrons leak out of nuclei and become free neutrons. As we dig dipper and dipper, the nuclei becomes smaller and smaller until the core is reached where nuclei disappear. The composition of the super dense core remains uncertain.
Here is a sample calculation. We can get something like several rotations per second!!!
Here is a link to the interactive CDF file to explore magnetic field of neutron star with different parameters.
Click here to download
Sources
Wikipedia Neutron Star
Magnetic Field of a rotating Sphere Estimates
To understand why a neutron star has a huge magnetic field, let's look at its structure.
The structure
A little deeper into the star, the gravity gets strong enough so that neutrons leak out of nuclei and become free neutrons. As we dig dipper and dipper, the nuclei becomes smaller and smaller until the core is reached where nuclei disappear. The composition of the super dense core remains uncertain.
Angular velocity
To get a rough estimate of angular velocity, we can assume that angular velocity is conserved.Here is a sample calculation. We can get something like several rotations per second!!!
Magnetic Field
Here is a rough calculations of neutron stars' magnetic field assuming charge density is uniform in spherical shell shape. This shell can have a lot of surface charge density since there is a sea of electrons. If we estimate the magnetic field of rotating charged sphere, then the below picture shows that neutron stars can have magnetic fields like 50,000 Tesla. Compare that to earth's magnetic field (0.0001 Tesla) or maximum magnetic field produced on earth (100 Tesla).
Here is a link to the interactive CDF file to explore magnetic field of neutron star with different parameters.
Click here to download
Sources
Wikipedia Neutron Star
Magnetic Field of a rotating Sphere Estimates
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