Asteroseismology can reveal strong internal magnetic fields in red giant stars

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Science  23 Oct 2015:
Vol. 350, Issue 6259, pp. 423-426
DOI: 10.1126/science.aac6933

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Stellar oscillations as magnetic probes

Unlike magnetic fields on the surfaces of stars, those within a star have so far remained difficult to observe. Fuller et al. have developed a method of delving into the magnetic depths by exploiting the oscillations of red giant stars. A high magnetic field can cause sound waves to become trapped within the central regions of the star, damping certain vibration modes. Using seismological techniques, this suppression can help infer the core magnetic field for several red giants.

Science, this issue p. 423


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.

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