Asteroseismology Can Reveal Strong Internal Magnetic Fields in Red Giant Stars

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 $\approx \! \! 10^7 \,{\rm G}$.

Published in Science on October 23, 2015, available at http://www.sciencemag.org/content/350/6259/423.short. This is the authors' version of the manuscript. Authorea version of the paper, including supplementary material, ancillary data and a layman summary, can be found at https://www.authorea.com/83992