The effects of surface fossil magnetic fields on massive star evolution

speaker: Zsolt Keszthelyi

Abstract :

Magnetism plays a vital role in several astrophysical phenomena, from the scale of sub-atomic particles up to galaxy clusters. Studying stellar magnetic fields can help us better understand planetary habitability, stellar variability, and the overall magnetic flux evolution from star formation to compact objects.
There has been renewed interest in this field, partly due to the surprising discovery that some massive stars host strong, globally organized, large-scale magnetic fields. The long-term (years to decades-long) spectropolarimetric monitoring shows a lack of correlation with stellar parameters. This suggests that the observed fields of early-type stars are not produced by a dynamo mechanism. Instead, they are thought to be remnants from the earlier history of the star (from the star formation phase or, in part, produced by stellar mergers).
In a series of publications, we have been studying the long-term, evolutionary impact of such fossil fields on massive star evolution. Two main effects concern i) trapping wind material and thus reducing the mass loss and ii) magnetic braking leading to slowly spinning stars. Both have far-reaching consequences and could affect completely evolutionary pathways, stellar populations, predictions on stellar end products, and gravitational wave progenitors.
We recently computed and scrutinized a grid of models including these effects in three metallicity environments. The library of new stellar models is open source and available for the community via: https://zenodo.org/record/7069766