Abstract
A red giant star is an evolved low- or intermediate-mass star that has exhausted its central hydrogen content, leaving a helium core and a hydrogen-burning shell. Oscillations of stars can be observed as periodic dimmings and brightenings in the optical light curves. In red giant stars, non-radial acoustic waves couple to gravity waves and give rise to mixed modes, which behave as pressure modes in the envelope and gravity modes in the core. These modes have previously been used to measure the internal rotation of red giants1,2, leading to the conclusion that purely hydrodynamical processes of angular momentum transport from the core are too inefficient3. Magnetic fields could produce the additional required transport4,5,6. However, owing to the lack of direct measurements of magnetic fields in stellar interiors, little is currently known about their properties. Asteroseismology can provide direct detection of magnetic fields because, like rotation, the fields induce shifts in the oscillation mode frequencies7,8,9,10,11,12. Here we report the measurement of magnetic fields in the cores of three red giant stars observed with the Kepler13 satellite. The fields induce shifts that break the symmetry of dipole mode multiplets. We thus measure field strengths ranging from about 30 kilogauss to about 100 kilogauss in the vicinity of the hydrogen-burning shell and place constraints on the field topology.
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Data availability
Kepler data are publicly available from the Mikulski Archive for Space Telescopes (MAST) portal at https://archive.stsci.edu. Spectra are available at https://doi.org/10.5281/zenodo.6818371.
Code availability
This study makes use of the stellar evolution code MESA, which is available at https://docs.mesastar.org.
References
Deheuvels, S. et al. Seismic evidence for a rapidly rotating core in a lower-giant-branch star observed with Kepler. Astrophys. J. 756, 19 (2012).
Gehan, C., Mosser, B., Michel, E., Samadi, R. & Kallinger, T. Core rotation braking on the red giant branch for various mass ranges. Astron. Astrophys. 616, A24 (2018).
Marques, J. P. et al. Seismic diagnostics for transport of angular momentum in stars. I. Rotational splittings from the pre-main sequence to the red-giant branch. Astron. Astrophys. 549, A74 (2013).
Gough, D. O. & McIntyre, M. E. Inevitability of a magnetic field in the Sun’s radiative interior. Nature 394, 755–757 (1998).
Fuller, J., Piro, A. L. & Jermyn, A. S. Slowing the spins of stellar cores. Mon. Not. R. Astron. Soc. 485, 3661–3680 (2019).
Gouhier, B., Jouve, L. & Lignières, F. Angular momentum transport in a contracting stellar radiative zone embedded in a large scale magnetic field. Astron. Astrophys. 661, A119 (2022).
Unno, W., Osaki, Y., Ando, H., Saio, H. & Shibahashi, H. Nonradial Oscillations of Stars (Univ. Tokyo Press, 1989).
Gough, D. O. & Thompson, M. J. The effect of rotation and a buried magnetic field on stellar oscillations. Mon. Not. R. Astron. Soc. 242, 25–55 (1990).
Hasan, S. S., Zahn, J. P. & Christensen-Dalsgaard, J. Probing the internal magnetic field of slowly pulsating B-stars through g modes. Astron. Astrophys. 444, L29–L32 (2005).
Gomes, P. & Lopes, I. Core magnetic field imprint in the non-radial oscillations of red giant stars. Mon. Not. R. Astron. Soc. 496, 620–628 (2020).
Bugnet, L. et al. Magnetic signatures on mixed-mode frequencies. I. An axisymmetric fossil field inside the core of red giants. Astron. Astrophys. 650, A53 (2021).
Loi, S. T. Topology and obliquity of core magnetic fields in shaping seismic properties of slowly rotating evolved stars. Mon. Not. R. Astron. Soc. 504, 3711–3729 (2021).
Borucki, W. J. et al. Kepler planet-detection mission: introduction and first results. Science 327, 977–980 (2010).
Mathis, S. et al. Probing the internal magnetism of stars using asymptotic magneto-asteroseismology. Astron. Astrophys. 647, A122 (2021).
Deheuvels, S., Ouazzani, R. M. & Basu, S. Near-degeneracy effects on the frequencies of rotationally-split mixed modes in red giants. Astron. Astrophys. 605, A75 (2017).
Dziembowski, W. A. & Goode, P. R. Effects of differential rotation on stellar oscillations: a second-order theory. Astrophys. J. 394, 670 (1992).
Paxton, B. et al. Modules for Experiments in Stellar Astrophysics (MESA). Astrophys. J. Suppl. Ser. 192, 3 (2011).
Mosser, B. et al. Period spacings in red giants. IV. Toward a complete description of the mixed-mode pattern. Astron. Astrophys. 618, A109 (2018).
Takata, M. Asymptotic analysis of dipolar mixed modes of oscillations in red giant stars. Publ. Astron. Soc. Jpn 68, 109 (2016).
Fuller, J., Cantiello, M., Stello, D., Garcia, R. A. & Bildsten, L. Asteroseismology can reveal strong internal magnetic fields in red giant stars. Science 350, 423–426 (2015).
Stello, D. et al. A prevalence of dynamo-generated magnetic fields in the cores of intermediate-mass stars. Nature 529, 364–367 (2016).
Donati, J. F. & Landstreet, J. D. Magnetic fields of nondegenerate stars. Annu. Rev. Astron. Astrophys. 47, 333–370 (2009).
Braithwaite, J. & Spruit, H. C. Magnetic fields in non-convective regions of stars. R. Soc. Open Sci. 4, 160271 (2017).
Becerra, L., Reisenegger, A., Valdivia, J. A. & Gusakov, M. E. Evolution of random initial magnetic fields in stably stratified and barotropic stars. Mon. Not. R. Astron. Soc. 511, 732–745 (2022).
Cantiello, M., Fuller, J. & Bildsten, L. Asteroseismic signatures of evolving internal stellar magnetic fields. Astrophys. J. 824, 14 (2016).
Brun, A. S., Browning, M. K. & Toomre, J. Simulations of core convection in rotating A-type stars: magnetic dynamo action. Astrophys. J. 629, 461–481 (2005).
Aurière, M. et al. Weak magnetic fields in Ap/Bp stars. Evidence for a dipole field lower limit and a tentative interpretation of the magnetic dichotomy. Astron. Astrophys. 475, 1053–1065 (2007).
Deheuvels, S. et al. Seismic constraints on the radial dependence of the internal rotation profiles of six Kepler subgiants and young red giants. Astron. Astrophys. 564, A27 (2014).
Mosser, B., Vrard, M., Belkacem, K., Deheuvels, S. & Goupil, M. J. Period spacings in red giants. I. Disentangling rotation and revealing core structure discontinuities. Astron. Astrophys. 584, A50 (2015).
Acknowledgements
We acknowledge support from from the project BEAMING ANR-18-CE31-0001 of the French National Research Agency (ANR) and from the Centre National d’Etudes Spatiales (CNES).
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Contributions
G.L. discovered the three stars with asymmetric splittings. G.L. and S.D. measured the asymmetries and rotation rates. S.D. measured the absolute magnetic shifts and supervised the whole project. J.B. and F.L. developed the theoretical framework used to interpret the observations. All the authors contributed to writing the manuscript.
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Nature thanks Matteo Cantiello, Margarida Cunha and the other, anonymous, reviewer(s) for their contribution to the peer review of this work. Peer reviewer reports are available.
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Extended data figures and tables
Extended Data Fig. 1 Shape of the weight function K(m) as a function of the normalized mass.
The function K(m) is shown for the stellar model representative of KIC 11515377. The blue shaded region indicates the hydrogen-burning shell. The vertical dashed line corresponds to the maximal extent of the initial convective core at the beginning of the main sequence.
Extended Data Fig. 2 Multiplet asymmetries in KIC 11515377 as a function of mode frequency.
Symbols have the same meaning as in Fig. 2.
Extended Data Fig. 3 Multiplet asymmetries in KIC 7518143 as a function of mode frequency.
Symbols have the same meaning as in Fig. 2.
Extended Data Fig. 4 Stretched échelle diagram for KIC 11515377.
Symbols have the same meaning as in Fig. 3.
Extended Data Fig. 5 Stretched échelle diagram for KIC 7518143.
Symbols have the same meaning as in Fig. 3.
Supplementary information
Supplementary Information
Supplementary Sections 1–7, including Supplementary Figs. 1–6 and Tables 1–7.
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Li, G., Deheuvels, S., Ballot, J. et al. Magnetic fields of 30 to 100 kG in the cores of red giant stars. Nature 610, 43–46 (2022). https://doi.org/10.1038/s41586-022-05176-0
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DOI: https://doi.org/10.1038/s41586-022-05176-0
