2004/10/01 by Jonathan Braithwaite, J. Braithwaite, H. C. Spruit +1 · 6 citations
Physics and Astronomy · #Astro and Planetary Science #Solar and Space Plasma Dynamics #Stellar, planetary, and galactic studies #astro-ph
paper · pdf · doi:10.1038/nature02934
published as Nature 431 (2004) 819 · Appeared in Nature, 431, 819 (2004)
openalex publication_date 2004/10/01 · arxiv created 2005/02/02 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/01
Some main-sequence stars of spectral type A are observed to have a strong (300-30000 G), static, large-scale magnetic field, of a chiefly dipolar shape -- the `Ap stars' (for example Alioth, the fifth star in the Big Dipper). Following their discovery fifty years ago, it was speculated that these fields a remnants of the star's formation, a `fossil' field. Alternatively, they could be generated by a dynamo process in the star's convective core. The dynamo hypothesis has difficulty explaining high field strengths and the lack of a correlation with rotation. The weakness of the fossil-field theory has been the absence of known field configurations stable enough to survive in a star over its lifetime. We demonstrate here the formation of stable magnetic field configurations, with properties agreeing with those observed, by evolution from arbitrary, unstable initial fields. The results are applicable equally to Ap stars, magnetic white dwarfs and some highly magnetised neutron stars known as magnetars. This establishes fossil fields as the natural, unifying explanation for the magnetism of all these stars.