Origin of magnetic fields in magnetic white dwarfs

Determine the physical origin of the powerful magnetic fields observed in magnetic white dwarfs, identifying which mechanisms—such as fossil fields from progenitors, crystallization-driven dynamos, or common-envelope dynamos—are responsible and under what evolutionary conditions they operate.

Background

Magnetic white dwarfs exhibit surface fields spanning 10^3–10^9 G, with many objects showing complex, non-dipolar structures. Several formation channels have been proposed, including inheritance of fossil fields from progenitors, dynamo action during crystallization, and dynamos active in common-envelope phases of binary evolution.

Understanding the origin of these fields is crucial for modeling magnetospheric environments that influence weakly interacting slim particle (WISP) searches, including axion–photon conversion signatures in X-ray and polarization observables. Despite multiple hypotheses, a definitive, unifying explanation for the observed magnetic field strengths and geometries in magnetic white dwarfs has not yet been established.