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Earth’s nearest candidate supermassive black hole lies at the centre of the Milky Way1. Its electromagnetic emission is thought to be powered by radiatively inefficient accretion of gas from its environment2, which is a standard mode of energy supply for most galactic nuclei. X-ray measurements have already resolved a tenuous hot gas component from which the black hole can be fed3. The magnetization of the gas, however, which is a crucial parameter determining the structure of the accretion flow, remains unknown. Strong magnetic fields can influence the dynamics of accretion, remove angular momentum from the infalling gas4, expel matter through relativistic jets5 and lead to synchrotron emission such as that previously observed6,7,8. Here we report multi-frequency radio measurements of a newly discovered pulsar close to the Galactic Centre9,10,11,12 and show that the pulsar’s unusually large Faraday rotation (the rotation of the plane of polarization of the emission in the presence of an external magnetic field) indicates that there is a dynamically important magnetic field near the black hole. If this field is accreted down to the event horizon it provides enough magnetic flux to explain the observed emission—from radio to X-ray wavelengths—from the black hole.

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  • 20 August 2013

    Source Data files for Figs 1–3 were added.


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We wish to thank D. D. Xu., P. Lazarus and L. Guillemot for discussions. We also thank O. Wucknitz and R. Beck for reading the manuscript. R.K., L.G.S. and P.C.C.F. gratefully acknowledge financial support from the European Research Council for the ERC Starting Grant BEACON under contract no. 279702. K.J.L. was funded by ERC Advanced Grant LEAP under contract no. 227947. H.F. acknowledges funding from an Advanced Grant of the European Research Council under the European Union’s Seventh Framework Programme (FP/2007-2013)/ERC Grant Agreement no. 227610. This work was based on observations with the 100-m telescope of the MPIfR (Max-Planck-Institut für Radioastronomie) at Effelsberg. The Nançay radio telescope is part of the Paris Observatory, associated with the Centre National de la Recherche Scientifique (CNRS), and partly supported by the Région Centre in France. The National Radio Astronomy Observatory (NRAO) is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.

Author information


  1. Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn, Germany

    • R. P. Eatough
    • , H. Falcke
    • , R. Karuppusamy
    • , K. J. Lee
    • , D. J. Champion
    • , G. Desvignes
    • , D. H. F. M. Schnitzeler
    • , L. G. Spitler
    • , M. Kramer
    • , B. Klein
    • , A. Brunthaler
    • , P. C. C. Freire
    • , A. Kraus
    • , A. Noutsos
    •  & N. Wex
  2. Department of Astrophysics, Institute for Mathematics, Astrophysics and Particle Physics, Radboud University, PO Box 9010, 6500 GL Nijmegen, The Netherlands

    • H. Falcke
  3. ASTRON, PO Box 2, 7990 AA Dwingeloo, The Netherlands

    • H. Falcke
    •  & A. T. Deller
  4. Jodrell Bank Centre for Astrophysics, School of Physics and Astronomy, The University of Manchester, Manchester M13 9PL, UK

    • E. F. Keane
    • , M. Kramer
    • , C. Bassa
    • , A. G. Lyne
    •  & B. Stappers
  5. Bonn-Rhein-Sieg University of Applied Sciences, Grantham-Allee 20, D-53757 Sankt Augustin, Germany

    • B. Klein
  6. Astronomy Department, B-20 Hearst Field Annex, University of California, Berkeley, California 94720-3411, USA

    • G. C. Bower
  7. LPC2E/CNRS - Université d’Orléans, 45071 Orléans, France

    • I. Cognard
  8. Nançay/Paris Observatory, 18330 Nançay, France

    • I. Cognard
  9. National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, Virginia 22903, USA

    • P. B. Demorest


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R.P.E.: initial detections, observations performed at Effelsberg and data processing; H.F.: observational and theoretical background and paper formulation; R.K.: observational technical assistance and pulsar timing; K.J.L.: polarization and RM measurements; D.J.C.: pulsar timing solution; E.F.K.: flux density calculations, observational assistance and observations at Jodrell Bank; G.D.: observations at Nançay; D.H.F.M.S.: observational background and RM interpretation; L.G.S.: observational background and data processing and analysis; M.K.: observational background and RM interpretation; B.K.: technical observational assistance at Effelsberg; C.B.: observations at Jodrell Bank; G.C.B.: observations at the VLA and RM interpretation; A.B.: observations at the VLA; I.C.: observations at Nançay; A.T.D.: observations at the VLA; P.B.D.: observations at the VLA; P.C.C.F.: observational background and pulsar timing; A.K.: technical observational assistance at Effelsberg; A.G.L.: observations at Jodrell Bank and help with initial detections; A.N.: observational background and RM interpretation; B.S.: observations at Jodrell Bank; N.W.: theoretical background and orbital characteristics.

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The authors declare no competing financial interests.

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Correspondence to R. P. Eatough.

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