White Dwarf Magnetism

The magnetic fields of some white dwarfs are more than a million times stronger than the Earth's. The origin of white dwarf magnetism is still a puzzle; a possible mechanism is the crystallization-driven dynamo.

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Most white dwarfs are made of carbon and oxygen. As a white dwarf cools down, its core begins to crystallize (solidify). The crystal phase is slightly enriched in oxygen, generating an unstable composition gradient in the liquid above (a heavier element on top of a lighter one), which drives convection. This convection, when combined with the white dwarf's rotation, can generate a strong magnetic field.

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See Ginzburg, Fuller, Kawka, Caiazzo (2022) for details.