On large-scale dynamos with stable stratification and the application to stellar radiative zones

V. Skoutnev, J. Squire, A. Bhattacharjee

Research output: Contribution to journalArticlepeer-review

5 Scopus citations

Abstract

Our understanding of large-scale magnetic fields in stellar radiative zones remains fragmented and incomplete. Such magnetic fields, which must be produced by some form of dynamo mechanism, are thought to dominate angular-momentum transport, making them crucial to stellar evolution. A major difficulty is the effect of stable stratification, which generally suppresses dynamo action. We explore the effects of stable stratification on mean-field dynamo theory with a particular focus on a non-helical large-scale dynamo (LSD) mechanism known as the magnetic shear-current effect. We find that the mechanism is robust to increasing stable stratification as long as the original requirements for its operation are met: A source of shear and non-helical magnetic fluctuations (e.g. from a small-scale dynamo). Both are plausibly sourced in the presence of differential rotation. Our idealized direct numerical simulations, supported by mean-field theory, demonstrate the generation of near equipartition large-scale toroidal fields. Additionally, a scan over magnetic Reynolds number shows no change in the growth or saturation of the LSD, providing good numerical evidence of a dynamo mechanism resilient to catastrophic quenching, which has been an issue for helical dynamos. These properties-the absence of catastrophic quenching and robustness to stable stratification-make the mechanism a plausible candidate for generating in situ large-scale magnetic fields in stellar radiative zones.

Original languageEnglish (US)
Pages (from-to)526-542
Number of pages17
JournalMonthly Notices of the Royal Astronomical Society
Volume517
Issue number1
DOIs
StatePublished - Nov 1 2022

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

Keywords

  • MHD
  • dynamo
  • stars: interiors

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