Resonant Instability of mixed poloidal-toroidal magnetic configurations

We present a global linear analysis of a resonant magnetic instability of mixed poloidal–toroidal field configurations within radiative stellar interiors. This instability, previously studied in cylindrical geometry in the context of fusion physics but largely unexplored in astrophysical contexts, arises when the stability condition known as the Suydam criterion is violated. The instability is resonant in nature, appearing only for a narrow band of wavenumbers that satisfy the condition k · B ≈ 0, leading to perturbations that propagate almost perpendicularly to the magnetic field. This instability displays dynamical properties similar to the Tayler instability, notably its resilience against suppression by stable stratification. However, unlike Tayler modes, it can remain active even in the presence of a relatively strong poloidal field. Our results suggest that resonant magnetic instabilities may allow us to better understand the magnetic and rotational evolution of radiative stellar interiors, and deserve further investigation in both linear and nonlinear regimes.