Letter | Published:

A kilonova as the electromagnetic counterpart to a gravitational-wave source

Nature volume 551, pages 7579 (02 November 2017) | Download Citation


Gravitational waves were discovered with the detection of binary black-hole mergers1 and they should also be detectable from lower-mass neutron-star mergers. These are predicted to eject material rich in heavy radioactive isotopes that can power an electromagnetic signal. This signal is luminous at optical and infrared wavelengths and is called a kilonova2,3,4,5. The gravitational-wave source GW170817 arose from a binary neutron-star merger in the nearby Universe with a relatively well confined sky position and distance estimate6. Here we report observations and physical modelling of a rapidly fading electromagnetic transient in the galaxy NGC 4993, which is spatially coincident with GW170817 and with a weak, short γ-ray burst7,8. The transient has physical parameters that broadly match the theoretical predictions of blue kilonovae from neutron-star mergers. The emitted electromagnetic radiation can be explained with an ejected mass of 0.04 ± 0.01 solar masses, with an opacity of less than 0.5 square centimetres per gram, at a velocity of 0.2 ± 0.1 times light speed. The power source is constrained to have a power-law slope of −1.2 ± 0.3, consistent with radioactive powering from r-process nuclides. (The r-process is a series of neutron capture reactions that synthesise many of the elements heavier than iron.) We identify line features in the spectra that are consistent with light r-process elements (atomic masses of 90–140). As it fades, the transient rapidly becomes red, and a higher-opacity, lanthanide-rich ejecta component may contribute to the emission. This indicates that neutron-star mergers produce gravitational waves and radioactively powered kilonovae, and are a nucleosynthetic source of the r-process elements.

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This work is based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere, Chile, as part of ePESSTO (the extended Public ESO Spectroscopic Survey for Transient Objects Survey) ESO programme 199.D-0143 and 099.D-0376. We thank ESO staff for their support at La Silla and Paranal and for making the NACO and VISIR data public to LIGO–Virgo collaborating scientists. We thank J. Ward for permitting a time switch on the NTT. Part of the funding for GROND was generously granted from the Leibniz Prize to G. Hasinger (DFG grant HA 1850/28-1). Pan-STARRS1 and ATLAS are supported by NASA grants NNX08AR22G, NNX12AR65G, NNX14AM74G and NNX12AR55G issued through the SSO Near Earth Object Observations Program. We acknowledge help in obtaining GROND data from A. Hempel, M. Rabus and R. Lachaume on La Silla. The Pan-STARRS1 Surveys were made possible by the IfA, University of Hawaii, the Pan-STARRS Project Office, the Max-Planck Society, MPIA Heidelberg and MPE Garching, Johns Hopkins University, Durham University, the University of Edinburgh, Queen’s University Belfast, Harvard-Smithsonian Center for Astrophysics, Las Cumbres Observatory Global Telescope Network Incorporated, National Central University of Taiwan, Space Telescope Science Institute, the National Science Foundation under grant number AST-1238877, the University of Maryland, and Eotvos Lorand University (ELTE) and the Los Alamos National Laboratory. We acknowledge EU/FP7-ERC grants 291222 and 615929 and STFC funding through grants ST/P000312/1 and ERF ST/M005348/1. A.J. acknowledges Marie Sklodowska-Curie grant number 702538. M.G., A.H., K.A.R. and Ł.W. acknowledge the Polish NCN grant OPUS 2015/17/B/ST9/03167, J.S. is funded by the Knut and Alice Wallenberg Foundation. C.B., M.D.V., N.E.-R., A.P. and G.T. are supported by the PRIN-INAF 2014. M.C. is supported by the David and Ellen Lee Prize Postdoctoral Fellowship at the California Institute of Technology. M.F. is supported by a Royal Society Science Foundation Ireland University Research Fellowship. M.S. and C.I. acknowledge support from EU/FP7-ERC grant number 615929. P.G.J. acknowledges the ERC consolidator grant number 647208. GREAT is funded by V.R. J.D.L. acknowledges STFC grant ST/P000495/1. T.W.C., P.S. and P.W. acknowledge support through the Alexander von Humboldt Sofja Kovalevskaja Award. J.H. acknowledges financial support from the Vilho, Yrjö and Kalle Väisälä Foundation. J.V. acknowledges FONDECYT grant number 3160504. L.G. was supported in part by the US National Science Foundation under grant AST-1311862. MB acknowledges support from the Swedish Research Council and the Swedish Space Board. A.G.-Y. is supported by the EU via ERC grant number 725161, the Quantum Universe I-Core programme, the ISF, the BSF and by a Kimmel award. L.S. acknowledges IRC grant GOIPG/2017/1525. A.J.R. is supported by the Australian Research Council Centre of Excellence for All-sky Astrophysics (CAASTRO) through project number CE110001020. I.R.S. was supported by the Australian Research Council grant FT160100028. We acknowledge Millennium Science Initiative grant IC120009. This paper uses observations obtained at the Boyden Observatory, University of the Free State, South Africa.

Author information


  1. Astrophysics Research Centre, School of Mathematics and Physics, Queens University Belfast, Belfast BT7 1NN, UK

    • S. J. Smartt
    • , E. Kankare
    • , S. A. Sim
    • , K. Maguire
    • , M. Magee
    • , L. J. Shingles
    • , K. W. Smith
    • , D. R. Young
    • , R. Kotak
    • , P. Clark
    • , O. McBrien
    •  & D. O’Neill
  2. Max-Planck-Institut für Extraterrestrische Physik, Giessenbach-Strasse 1, D-85748 Garching, Munich, Germany

    • T.-W. Chen
    • , T. Krühler
    • , J. Greiner
    • , A. Rau
    • , P. Schady
    • , T. Schweyer
    •  & P. Wiseman
  3. Max-Planck Institut für Astrophysik, Karl-Schwarzschild-Strasse 1, D-85748 Garching, Munich, Germany

    • A. Jerkstrand
    • , A. Flörs
    •  & S. Taubenberger
  4. LIGO Laboratory West Bridge, Room 257 California Institute of Technology, MC 100-36, Pasadena, California 91125, USA

    • M. Coughlin
  5. School of Physics, O’Brien Centre for Science North, University College Dublin, Belfield, Dublin 4, Ireland

    • M. Fraser
    • , L. Hanlon
    • , A. Martin-Carrillo
    •  & L. Salmon
  6. Department of Physics and Astronomy, University of Southampton, Southampton SO17 1BJ, UK

    • C. Inserra
    • , C. R. Angus
    • , R. Cartier
    • , G. Dimitriadis
    • , R. E. Firth
    • , C. P. Gutiérrez
    • , M. Smith
    •  & M. Sullivan
  7. Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, Hawaii 96822, USA.

    • K. C. Chambers
    • , M. E. Huber
    • , J. Tonry
    • , J. Bulger
    • , L. Denneau
    • , H. Flewelling
    • , A. Heinze
    • , T. B. Lowe
    • , E. A. Magnier
    • , A. S. B. Schultz
    • , R. J. Wainscoat
    • , C. Waters
    • , H. Weiland
    •  & M. Willman
  8. Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, 2100 Copenhagen Ø, Denmark

    • G. Leloudas
    •  & K. E. Heintz
  9. Department of Particle Physics and Astrophysics, Weizmann Institute of Science, Rehovot 76100, Israel

    • A. Gal-Yam
    • , I. Manulis
    •  & O. Yaron
  10. Department of Physics, University of Warwick, Coventry CV4 7AL, UK.

    • J. D. Lyman
  11. Institute for Astronomy, SUPA (Scottish Universities Physics Alliance), University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ, UK

    • D. S. Homan
    •  & A. Lawrence
  12. Departamento de Ciencias Fisicas, Universidad Andres Bello, Avenida de Republica 252, Santiago, Chile

    • C. Agliozzo
    •  & G. Pignata
  13. Millennium Institute of Astrophysics (MAS), Nuncio Monseñor Sótero Sanz 100, Providencia, Santiago, Chile

    • C. Agliozzo
    • , F. E. Bauer
    •  & G. Pignata
  14. European Southern Observatory, Alonso de Córdova 3107, Casilla 19, Santiago, Chile

    • J. P. Anderson
    •  & A. Razza
  15. Astrophysics Research Institute, Liverpool John Moores University, IC2, Liverpool Science Park, 146 Brownlow Hill, Liverpool L3 5RF, UK

    • C. Ashall
    • , P. A. James
    •  & S. J. Prentice
  16. The Oskar Klein Centre, Department of Astronomy, Stockholm University, AlbaNova, 10691 Stockholm, Sweden

    • C. Barbarino
    • , R. Roy
    • , J. Sollerman
    •  & F. Taddia
  17. Instituto de Astrofísica and Centro de Astroingeniería, Facultad de Física, Pontificia Universidad Católica de Chile, Casilla 306, Santiago 22, Chile

    • F. E. Bauer
  18. Space Science Institute, 4750 Walnut Street, Suite 205, Boulder, Colorado 80301, USA

    • F. E. Bauer
  19. Dipartimento di Fisica e Astronomia ‘G. Galilei’, Università di Padova, Vicolo dell’Osservatorio 3, 35122 Padova, Italy

    • M. Berton
  20. INAF — Osservatorio Astronomico di Brera, via E. Bianchi 46, 23807 Merate, Italy

    • M. Berton
  21. INAF — Osservatorio Astronomico di Capodimonte, via Salita Moiariello 16, 80131 Napoli, Italy

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    •  & M. Della Valle
  22. The Oskar Klein Centre, Department of Physics, Stockholm University, AlbaNova, 10691 Stockholm, Sweden

    • M. Bulla
  23. SRON, Netherlands Institute for Space Research, Sorbonnelaan 2, NL-3584 CA Utrecht, The Netherlands

    • G. Cannizzaro
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    • , Z. Kostrzewa-Rutkowska
    •  & F. Onori
  24. Department of Astrophysics/IMAPP, Radboud University, PO Box 9010, NL-6500 GL Nijmegen, The Netherlands

    • G. Cannizzaro
    • , P. G. Jonker
    • , Z. Kostrzewa-Rutkowska
    •  & F. Onori
  25. Instituto de Astrofísica de Andalucía (IAA-CSIC), Glorieta de la Astronomía, E-18008 Granada, Spain

    • Z. Cano
    •  & L. Izzo
  26. European Southern Observatory, Karl-Schwarzschild Strasse 2, 85748 Garching bei München, Germany

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    • , A. De Cia
    • , A. Flörs
    • , A. Hamanowicz
    • , W. E. Kerzendorf
    • , F. Patat
    •  & S. Taubenberger
  27. ICRANet-Pescara, Piazza della Repubblica 10, I-65122 Pescara, Italy

    • M. Della Valle
  28. IAP/CNRS and University Pierre et Marie Curie, Paris, France

    • M. Dennefeld
  29. Unidad Mixta Internacional Franco-Chilena de Astronomía (CNRS UMI 3386), Departamento de Astronomía, Universidad de Chile, Camino El Observatorio 1515, Las Condes, Santiago, Chile

    • L. Dessart
  30. Istituto Nazionale di Astrofisica, Viale del Parco Mellini 84, I-00136 Roma, Italy

    • N. Elias-Rosa
  31. Physik-Department, Technische Universität München, James-Franck-Straße 1, 85748 Garching bei München, Germany

    • A. Flörs
  32. Deutsches Elektronen Synchrotron DESY, D-15738 Zeuthen, Germany

    • A. Franckowiak
    •  & M. Kowalski
  33. Institute of Cosmology and Gravitation, Dennis Sciama Building, University of Portsmouth, Burnaby Road, Portsmouth PO1 3FX, UK

    • C. Frohmaier
  34. PITT PACC, Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, USA

    • L. Galbany
  35. CENTRA, Instituto Superior Técnico — Universidade de Lisboa, Lisbon, Portugal

    • S. González-Gaitán
  36. Warsaw University Astronomical Observatory, Aleje Ujazdowskie 4, 00-478 Warszawa, Poland

    • M. Gromadzki
    • , A. Hamanowicz
    • , K. A. Rybicki
    •  & Ł. Wyrzykowski
  37. Thüringer Landessternwarte Tautenburg, Sternwarte 5, 07778 Tautenburg, Germany

    • A. Nicuesa Guelbenzu
    •  & S. Klose
  38. Tuorla observatory, Department of Physics and Astronomy, University of Turku, Väisäläntie 20, FI-21500 Piikkiö, Finland

    • J. Harmanen
    • , H. Kuncarayakti
    • , S. Mattila
    •  & T. Reynolds
  39. Centre for Astrophysics and Cosmology, Science Institute, University of Iceland, Dunhagi 5, 107 Reykjavík, Iceland

    • K. E. Heintz
  40. Instituto de Física y Astronomía, Universidad de Valparaiso, Gran Bretaña 1111, Playa Ancha, Valparaíso 2360102, Chile

    • M.-S. Hernandez
    •  & J. Vos
  41. Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK

    • S. T. Hodgkin
    •  & N. A. Walton
  42. Department of Physics, Lancaster University, Lancaster LA1 4YB, UK

    • I. M. Hook
  43. Institut fur Physik, Humboldt-Universitat zu Berlin, Newtonstrasse 15, D-12489 Berlin, Germany

    • M. Kowalski
    •  & J. Nordin
  44. Zentrum für Astronomie der Universität Heidelberg, Institut für Theoretische Astrophysik, Philosophenweg 12, 69120 Heidelberg, Germany

    • M. Kromer
  45. Heidelberger Institut für Theoretische Studien, Schloss-Wolfsbrunnenweg 35, 69118 Heidelberg, Germany

    • M. Kromer
  46. Finnish Centre for Astronomy with ESO (FINCA), University of Turku, Väisäläntie 20, 21500 Piikkiö, Finland

    • H. Kuncarayakti
  47. Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany

    • A. Müller
  48. Sorbonne Universités, UPMC Université Paris 6 and CNRS, UMR 7095, Institut d’Astrophysique de Paris, 98 bis boulevard Arago, 75014 Paris, France

    • J. T. Palmerio
  49. INAF-Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy

    • A. Pastorello
    • , M. L. Pumo
    •  & G. Terreran
  50. Department of Astrophysics, University of Oxford, Oxford OX1 3RH, UK

    • Ph. Podsiadlowski
  51. Università degli studi di Catania, DFA DIEEI, Via Santa Sofia 64, 95123 Catania, Italy

    • M. L. Pumo
  52. INFN-Laboratori Nazionali del Sud, Via Santa Sofia 62, 95123 Catania, Italy

    • M. L. Pumo
  53. Department of Astronomy, Universidad de Chile, Camino El Observatorio 1515, Las Condes, Santiago de Chile, Chile

    • A. Razza
  54. Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, Maryland 21218, USA

    • A. Rest
  55. Department of Physics and Astronomy, The Johns Hopkins University, 3400 North Charles Street, Baltimore, Maryland 21218, USA

    • A. Rest
  56. Inter-University Centre for Astronomy and Astrophysics (IUCAA), Pune 411007, India

    • R. Roy
  57. School of Physical, Environmental, and Mathematical Sciences, University of New South Wales, Australian Defence Force Academy, Canberra, Australian Capital Territory 2600, Australia

    • A. J. Ruiter
    •  & I. R. Seitenzahl
  58. Research School of Astronomy and Astrophysics, The Australian National University, Canberra, Australian Capital Territory 2611, Australia

    • A. J. Ruiter
    •  & I. R. Seitenzahl
  59. ARC Centre of Excellence for All-sky Astrophysics (CAASTRO)

    • A. J. Ruiter
  60. LSST, 950 North Cherry Avenue, Tucson, Arizona 85719, USA

    • B. Stalder
  61. Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA

    • C. W. Stubbs
  62. Department of Physics, University of the Free State, Bloemfontein 9300, South Africa

    • H. Szegedi
    •  & B. van Soelen
  63. Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA) and Department of Physics and Astronomy, Northwestern University, Evanston, Illinois 60208, USA

    • G. Terreran
  64. School of Physics and Astronomy, University of Minnesota, 116 Church Street SE, Minneapolis, Minnesota 55455-0149, USA

    • D. E. Wright


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S.J.S. is Principal Investigator of ePESSTO and co-lead for the Pan-STARRS gravitational-wave follow-up. S.J.S. led the writing of the text and managed the project. A.J. wrote the light curve fitting code, led the modelling and co-wrote the text. M.C. provided code for modelling and Markov chain Monte Carlo analysis, provided analysis and text. K.W. provided input. S.A.S., L.J.S. and M.M. did the TARDIS modelling, assisted by A.G.-Y. in line identification. T.-W.C., J.G., S.K., A.R., P.S., T.S., T.K., P.W. and A.N.G. managed, executed, reduced and provided GROND data. E.K., M.F., C.I., K.M., T.K. and G.L. reduced and analysed photometry and spectra and contributed to analysis, text and figures. K.W.S. and D.R.Y. ran data management for ATLAS and Pan-STARRS analysis. J.T. is the ATLAS lead and provided data. K.C.C. is the Pan-STARRS director, the co-lead of the gravitational-wave follow-up and managed the observing sequences. Pan-STARRS and ATLAS data and products were provided by the team of M.E.H., J.B., L.D., H.F., T.B.L., E.A.M., A.R., A.S.B.S., B.S., R.J.W., C.W., H.W., M.W. and D.E.W. C.W.S. is the ATLAS co-lead for the gravitational-wave follow-up and contributed to the text. O.M.B. and P.C. checked the ATLAS data for candidates and O.M.B. provided manuscript editing support. The ePESSTO project was delivered by the following, who have contributed to data, analysis and text comments: R.K., J.D.L., D.S.H., C.A., J.P.A., C.R.A., C.A., C.B., F.E.B., M.B., M.B., Z.C., R.C., A.C., P.C., A.D.C., M.T.B., M.D.V., M.D., G.D., N.E.-R., R.E.F., A. Flörs, A. Franckowiak, C.F., L.B., S.G.-G., M.G., C.P.G., A.H., J.H., K.E.H., A.H., M.-S.H., S.T.H., I.M.H., L.I., P.A.J., P.G.J., Z.K.-R., M. Kowalski, M. Kromer, H.K., A.L., I.M., S.M., J.N., D.O’N., F.O., J.T.P., A.P., F.P., G.P., M.L.P., S.J.P., T.R., R.R., A.J.R., K.A.R., I.R.S., M.S., J.S., M.S., F.T., S.T., G.T., J.V., N.A.W., Ł.W., O.Y., G.C. and A.R. P.P. provided text and analysis comments. The 1.5B telescope data were provided, reduced and analysed by L.H., A.M.-C., L.S., H.S. and B.v.S. A.M. reduced and analysed the NACO and VISIR data.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to S. J. Smartt.

Reviewer Information Nature thanks R. Chevalier, C. Miller and the other anonymous reviewer(s) for their contribution to the peer review of this work.

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