Starquakes Reveal Ancient Magnetic Fields in White Dwarfs
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- Lukas Einramhof and Lisa Bugnet at ISTA led a team that published theoretical models in Astronomy & Astrophysics connecting surface magnetism in white dwarfs to core magnetism in red giants, reviving a fossil field theory that had fallen out of fashion over the past decade.
- Asteroseismic data from starquakes allowed the team to probe the interiors of red giants — the dying progenitors of white dwarfs — and confirm that magnetic fields detected at the cores of those progenitors match fields that later surface on their white dwarf remnants.
- The team's simulations show that to connect core magnetism in red giants to surface magnetism in older white dwarfs, a larger fraction of a star's core must be magnetized, though not necessarily more strongly, and the fields form shell-like structures rather than being centered at a single point.
- The researchers argue that these magnetic fields must originate even earlier than the red giant phase — potentially early in a star's main-sequence life — and survive billions of years of stellar evolution to emerge as fossil fields on white dwarf surfaces.
- A key open question the team flagged: it remains unknown whether the sun's core is magnetic, and current models assume it is not — if it turns out to be magnetic, 'this information would change everything we know and all the models we've based our work on,' Einramhof said.
- The conclusion: 'Given how little we know at this stage, our work suggests that stars are most likely all magnetic. But we can't always detect this magnetism,' according to Einramhof, whose findings could reshape models of how stars like the sun will evolve and how long they live.
Why it matters: The fossil field theory had been sidelined for a decade in the white dwarf community, and this paper is the first to merge independent observations from red giant cores and white dwarf surfaces into a single framework. If the sun's core turns out to be magnetic — something the team says current models wrongly assume it isn't — stellar evolution timelines and the sun's projected engulfment of Earth could need to be revised. The work opens a new observational path for testing stellar interiors using asteroseismology.
