Asteroseismology can reveal strong internal magnetic fields in red giant stars

• Published in: Science (American Association for the Advancement of Science) Vol. 350; no. 6259; pp. 423 - 426
• Main Authors: Fuller, Jim, Cantiello, Matteo, Stello, Dennis, Garcia, Rafael A., Bildsten, Lars
• Format: Journal Article
• Language: English
• Published: United States American Association for the Advancement of Science 23.10.2015; The American Association for the Advancement of Science; American Association for the Advancement of Science (AAAS)
• Subjects: Astrophysics; Dipoles; Field strength; Giant stars; Magnetic fields; Oscillations; Red giant stars; Sciences of the Universe; Stellar magnetic fields; Stellar oscillations; Vibration mode
• ISSN: 0036-8075; 1095-9203
• DOI: 10.1126/science.aac6933

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, arising 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 that field strengths larger than ∼105 gauss may produce the observed depression, and in one case we infer a minimum core field strength of ≈107 gauss.