Asteroseismology Can Reveal Strong Internal Magnetic Fields in Red Giant Stars

TL;DR

This paper shows that asteroseismology can detect strong internal magnetic fields in red giant stars by observing depressed dipole oscillation modes caused by magnetic effects in the core.

Contribution

It introduces a method to identify strong core magnetic fields in red giants through asteroseismic observations, revealing fields larger than 10^5 G.

Findings

Depressed dipole modes indicate strong core magnetic fields.

Core magnetic fields >10^5 G can cause observable mode depression.

Minimum inferred core field strength is approximately 10^7 G.

Abstract

Internal stellar magnetic fields are inaccessible to direct observations and little is known about their amplitude, geometry and evolution. We demonstrate that strong magnetic fields in the cores of red giant stars can be identified with asteroseismology. The fields can manifest themselves via depressed dipole stellar oscillation modes, which arises from a magnetic greenhouse effect that scatters and traps oscillation mode energy within the core of the star. The Kepler satellite has observed a few dozen red giants with depressed dipole modes which we interpret as stars with strongly magnetized cores. We find field strengths larger than $\sim\! 10^5 \,{\rm G}$ may produce the observed depression, and in one case we infer a minimum core field strength of $\approx \! \! 10^7 \,{\rm G}$.