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Abstract

When the core hydrogen is exhausted during stellar evolution, the central region of a star contracts and the outer envelope expands and cools, giving rise to a red giant. Convection takes place over much of the star’s radius. Conservation of angular momentum requires that the cores of these stars rotate faster than their envelopes; indirect evidence supports this1,2. Information about the angular-momentum distribution is inaccessible to direct observations, but it can be extracted from the effect of rotation on oscillation modes that probe the stellar interior. Here we report an increasing rotation rate from the surface of the star to the stellar core in the interiors of red giants, obtained using the rotational frequency splitting of recently detected ‘mixed modes’3,4. By comparison with theoretical stellar models, we conclude that the core must rotate at least ten times faster than the surface. This observational result confirms the theoretical prediction of a steep gradient in the rotation profile towards the deep stellar interior1,5,6.

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Acknowledgements

We acknowledge the work of the team behind Kepler. Funding for the Kepler Mission is provided by NASA's Science Mission Directorate. P.G.B. and C.A. were supported by the European Community’s Seventh Framework Programme (ERC grant PROSPERITY); J.D.R. and T.K. were supported by the Fund for Scientific Research, Flanders. S.H. was supported by the Netherlands Organisation for Scientific Research. J.M. and M.V. were supported by the Belgian Science Policy Office. The work is partly based on observations with the High Efficiency and Resolution Mercator Echelle Spectrograph at the Mercator Telescope, which is operated at La Palma in Spain by the Flemish Community.

Author information

Affiliations

  1. Instituut voor Sterrenkunde, Katholieke Universiteit Leuven, 3001 Leuven, Belgium

    • Paul G. Beck
    • , Thomas Kallinger
    • , Joris De Ridder
    • , Conny Aerts
    • , Fabien Carrier
    •  & Michel Hillen
  2. Institut d’Astrophysique et de Géophysique de l’Université de Liège, 4000 Liège, Belgium

    • Josefina Montalban
    • , Marc-Antoine Dupret
    •  & Marica Valentini
  3. Institut für Astronomie der Universität Wien, Türkenschanzstraße 17, 1180 Wien, Austria

    • Thomas Kallinger
  4. Afdeling Sterrenkunde, Institute for Mathematics Astrophysics and Particle Physics (IMAPP), Radboud University Nijmegen, 6500GL Nijmegen, The Netherlands

    • Conny Aerts
  5. Laboratoire Astrophysique, Instrumentation et Modélisation (AIM), CEA/DSM—CNRS—Université Paris Diderot; Institut de Recherche sur les lois Fondamentales de l'Univers/Service d’Astrophysique (IRFU/Sap), Centre de Saclay, 91191 Gif-sur-Yvette Cedex, France

    • Rafael A. García
  6. Astronomical Institute 'Anton Pannekoek', University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands

    • Saskia Hekker
  7. School of Physics and Astronomy, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK

    • Saskia Hekker
    • , Yvonne Elsworth
    •  & Andrea Miglio
  8. Laboratoire d’études spatiales et d’instrumentation (LESIA), CNRS, Université Pierre et Marie Curie, Université Denis Diderot, Observatoire de Paris, 92195 Meudon Cedex, France

    • Benoit Mosser
  9. Observatoire de Genève, Université de Genève, 51 Ch. des Maillettes, 1290 Sauverny, Switzerland

    • Patrick Eggenberger
  10. Sydney Institute for Astronomy (SIfA), School of Physics, University of Sydney 2006, Australia

    • Dennis Stello
    •  & Timothy R. Bedding
  11. Department of Physics and Astronomy, Aarhus University, DK-8000 Aarhus C, Denmark

    • Søren Frandsen
    • , Jørgen Christensen-Dalsgaard
    •  & Hans Kjeldsen
  12. Department of Astronomy and Physics, Saint Marys University, Halifax, NS B3H 3C3, Canada

    • Michael Gruberbauer
  13. Orbital Sciences Corporation/NASA Ames Research Center, Moffett Field, 94035 California, USA

    • Forrest R. Girouard
    • , Jennifer R. Hall
    •  & Khadeejah A. Ibrahim

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Contributions

P.G.B., T.K., J.D.R., C.A., R.A.G., S.H., B.M., Y.E., S.F., F.C. and M.G. measured the mode parameters, and derived and interpreted the rotational splitting and period spacings. J.M., M.-A.D., P.E., J.C.-D. and A.M. calculated stellar models and provided theoretical interpretation of the rotational splitting. M.H. and M.V. observed and analysed the spectra. J.D.R., S.H., S.F., Y.E., D.S., T.R.B., H.K., F.R.G., J.R.H. and K.A.I. contributed to the coordination of the project, including the acquisition and distribution of the data. C.A. defined and supervised the research. All authors discussed the results and commented on the manuscript.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Paul G. Beck.

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    Supplementary Information

    This file contains Supplementary Notes and Data , Supplementary References, Supplementary Tables 1-2 and Supplementary Figures 1-11 with legends.

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DOI

https://doi.org/10.1038/nature10612

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