An international research team led by Michael Kramer and Kuo Liu from the Max Planck Institute for Radio Astronomy in Bonn, Germany, have studied magnetars to uncover an underlying law that appears to apply universally to neutron stars.
Your last one is a good question. I don’t have an answer but I was leaning towards some sort of conservation law (e.g. normal stars have magnetic fields, when they get squeezed down to a neutron star those fields must go somewhere and it will be very much “concentrated”). Apparently this is a bit too easy (didn’t expect to be nothing different). Wikipedia provides a reference to a not too recent (2003) survey, namely this one: https://arxiv.org/abs/astro-ph/0307133 . I don’t know if it’s the state of the art but it surely is interesting.
Your last one is a good question. I don’t have an answer but I was leaning towards some sort of conservation law (e.g. normal stars have magnetic fields, when they get squeezed down to a neutron star those fields must go somewhere and it will be very much “concentrated”). Apparently this is a bit too easy (didn’t expect to be nothing different). Wikipedia provides a reference to a not too recent (2003) survey, namely this one: https://arxiv.org/abs/astro-ph/0307133 . I don’t know if it’s the state of the art but it surely is interesting.