Global simulations of Tayler instability in stellar interiors: the stabilizing effect of gravity
Abstract
Unveiling the evolution of toroidal field instability, known as Tayler instability, is essential to understand the strength and topology of the magnetic fields observed in earlytype stars, in the core of the red giants, or in any stellar radiative zone. We want to study the nonlinear evolution of the instability of a toroidal field stored in a stably stratified layer, in spherical symmetry and in the absence of rotation. In particular, we intend to quantify the suppression of the instability as a function of the BruntVäisäla (ω_{BV}) and the Alfvén (ω_{A}) frequencies. We use the magnetohydrodynamic (MHD) equations as implemented in the anelastic approximation in the EULAGMHD code and perform a large series of numerical simulations of the instability exploring the parameter space for the ω_{BV} and ω_{A}. We show that beyond a critical value gravity strongly suppress the instability, in agreement with the linear analysis. The intensity of the initial field also plays an important role: weaker fields show much slower growth rates. Moreover, in the case of very low gravity, the fastest growing modes have a large characteristic radial scale, at variance with the case of strong gravity, where the instability is characterized by horizontal displacements. Our results illustrate that the anelastic approximation can efficiently describe the evolution of toroidal field instability in stellar interiors. The suppression of the instability as a consequence of increasing values of ω_{BV} might play a role to explain the magnetic desert in Ap/Bp stars, since weak fields are only marginally unstable in the case of strong gravity.
 Publication:

Monthly Notices of the Royal Astronomical Society
 Pub Date:
 December 2019
 DOI:
 10.1093/mnras/stz2849
 arXiv:
 arXiv:1909.02897
 Bibcode:
 2019MNRAS.490.4281G
 Keywords:

 MHD;
 stars: magnetic field;
 Astrophysics  Solar and Stellar Astrophysics
 EPrint:
 11 pages, 11 figures, Accepted for publication in MNRAS