Magneto-Archaeology: New Models Link White Dwarf Fields to Their Giant Predecessors

An international team of scientists, led by experts from the Institute of Science and Technology Austria (ISTA), has presented theoretical models that, for the first time, establish a direct link between magnetic fields recorded on the surface of white dwarfs and fields discovered in the cores of their predecessors—red giants. The study's findings, published in the journal Astronomy & Astrophysics in early 2026, support the "fossil field" hypothesis, which posits that magnetic fields form during the early stages of a star's life and persist throughout its entire subsequent evolution.

The study, titled "Magneto-archaeology of white dwarfs," featuring key contributions from PhD student Lukas Einramhof and Assistant Professor Lisa Bugnet of ISTA, utilizes asteroseismology data to calibrate its calculations. This breakthrough is critical for understanding stellar evolution processes, including the distant future of our Sun, which is currently a 4.6-billion-year-old main-sequence star. Asteroseismic measurements, which analyze brightness fluctuations caused by acoustic and gravity waves, have provided evidence of strong magnetic fields within the radiative interiors of red giants.

As a white dwarf is the exposed core of a red giant that has shed its outer layers, the new research successfully reconciles field strengths measured in giant cores with those predicted for magnetized white dwarfs. This reinforces the "fossil field" theory as a plausible explanation for stellar magnetism. The team's modeling, specifically for a 1.5-solar-mass star, revealed that fields associated with the convective core during the main sequence would be "buried" too deep within the core during the red giant phase to match observed white dwarf fields.

Calculations demonstrate that if the field originated in the core during the main sequence or filled the radiative core as the star evolved along the red giant branch, the measured field strengths associated with the hydrogen-burning shell in red giants align with field amplitudes in magnetized white dwarfs. The simulations also suggest that magnetic fields may persist as shell-like structures where peripheral field strength exceeds that of the center, even after the outer envelopes are shed.

One of the primary unresolved questions is whether the Sun's core currently possesses a magnetic field, as standard models often assume it does not. The magnetization of the solar core could alter predictions of its longevity, potentially allowing the star to transport hydrogen into the inner core and thereby extend its lifespan. The ISTA study, partially funded by the European Research Council, provides clarity on the "magnetic memory" of stars, linking their past to the present throughout their life cycle.