Magnetic fields play a part in almost all stages of stellar evolution1. Most low-mass stars, including the Sun, show surface fields that are generated by dynamo processes in their convective envelopes2,3. Intermediate-mass stars do not have deep convective envelopes4, although 10 per cent exhibit strong surface fields that are presumed to be residuals from the star formation process5. These stars do have convective cores that might produce internal magnetic fields6, and these fields might survive into later stages of stellar evolution, but information has been limited by our inability to measure the fields below the stellar surface7. Here we report the strength of dipolar oscillation modes for a sample of 3,600 red giant stars. About 20 per cent of our sample show mode suppression, by strong magnetic fields in the cores8, but this fraction is a strong function of mass. Strong core fields occur only in red giants heavier than 1.1 solar masses, and the occurrence rate is at least 50 per cent for intermediate-mass stars (1.6–2.0 solar masses), indicating that powerful dynamos were very common in the previously convective cores of these stars.
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This paper has been written collaboratively, on the web, using Authorea (http://www.authorea.com). We acknowledge the entire Kepler team, whose efforts made these results possible. D.S. is the recipient of an Australian Research Council Future Fellowship (project number FT140100147). J.F. acknowledges support from NSF under grant number AST-1205732 and through a Lee DuBridge Fellowship at Caltech. R.A.G. acknowledges the support of the European Community’s Seventh Framework Programme (FP7/2007–2013) under grant agreement number 269194 (IRSES/ASK), the CNES, and the ANR-12-BS05-0008, IDEE. D.H. acknowledges support by the Australian Research Council’s Discovery Projects funding scheme (project number DE140101364) and support by the National Aeronautics and Space Administration under grant number NNX14AB92G issued through the Kepler Participating Scientist Program. This project was supported by NASA under TCAN grant number NNX14AB53G, and by the NSF under grant numbers PHY11-25915 and AST11-09174. Funding for the Stellar Astrophysics Centre is provided by The Danish National Research Foundation (grant agreement number DNRF106). The research is supported by the ASTERISK project (ASTERoseismic Investigations with SONG and Kepler) funded by the European Research Council (grant agreement number 267864).
The authors declare no competing financial interests.
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Stello, D., Cantiello, M., Fuller, J. et al. A prevalence of dynamo-generated magnetic fields in the cores of intermediate-mass stars. Nature 529, 364–367 (2016). https://doi.org/10.1038/nature16171
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