2.8 Degenerate stars

If the magnetic flux is conserved during stellar evolution, white dwarfs should be expected to have magnetic fields of 107  – 108 G. Yet, isolated magnetic white dwarfs are quite rare, comprising about 5% of all white dwarfs (Wickramasinghe and Ferrario, 2000). Observed spectral variations of magnetic white dwarfs on a timescale of hours or days suggest a complex magnetic field distribution on their surfaces. In some cases, spot-like magnetic field enhancements superimposed on a weaker dipole magnetic field can be identified (Landi Degl’Innocenti, 1976Maxted et al., 2000). Similar structures are most probably present on the surfaces of neutron stars as well. There is a growing evidence, based on X-ray and radio observations, that besides the large-scale dipolar magnetic field, isolated neutron stars possess small-scale magnetic field enhancements (Geppert et al., 2003). Current theory predicts that such structures can be generated from strong subsurface toroidal fields on both white dwarfs and neutron stars.

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