Letter | Published:

Optical emission from a kilonova following a gravitational-wave-detected neutron-star merger

Nature volume 551, pages 6466 (02 November 2017) | Download Citation


The merger of two neutron stars has been predicted to produce an optical–infrared transient (lasting a few days) known as a ‘kilonova’, powered by the radioactive decay of neutron-rich species synthesized in the merger1,2,3,4,5. Evidence that short γ-ray bursts also arise from neutron-star mergers has been accumulating6,7,8. In models2,9 of such mergers, a small amount of mass (10−4–10−2 solar masses) with a low electron fraction is ejected at high velocities (0.1–0.3 times light speed) or carried out by winds from an accretion disk formed around the newly merged object10,11. This mass is expected to undergo rapid neutron capture (r-process) nucleosynthesis, leading to the formation of radioactive elements that release energy as they decay, powering an electromagnetic transient1,2,3,9,10,11,12,13,14. A large uncertainty in the composition of the newly synthesized material leads to various expected colours, durations and luminosities for such transients11,12,13,14. Observational evidence for kilonovae has so far been inconclusive because it was based on cases15,16,17,18,19 of moderate excess emission detected in the afterglows of γ-ray bursts. Here we report optical to near-infrared observations of a transient coincident with the detection of the gravitational-wave signature of a binary neutron-star merger and with a low-luminosity short-duration γ-ray burst20. Our observations, taken roughly every eight hours over a few days following the gravitational-wave trigger, reveal an initial blue excess, with fast optical fading and reddening. Using numerical models21, we conclude that our data are broadly consistent with a light curve powered by a few hundredths of a solar mass of low-opacity material corresponding to lanthanide-poor (a fraction of 10−4.5 by mass) ejecta.

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We are indebted to W. Rosing and the LCO staff for making these observations possible, and to the LIGO and Virgo science collaborations. We thank L. Singer, T. Piran and W. Fong for assistance with planning the LCO observing program. We appreciate assistance and guidance from the LIGO–Virgo Collaboration—Electromagnetic follow-up liaisons. We thank B. Tafreshi and G. M. Árnason for helping to secure Internet connections in Iceland while this paper was being reviewed. Support for I.A. and J.B. was provided by the National Aeronautics and Space Administration (NASA) through the Einstein Fellowship Program (via grant numbers PF6-170148 and PF7-180162, respectively). G.H., D.A.H. and C.M. are supported by US National Science Foundation (NSF) grant AST-1313484. D.P. and D.M. acknowledge support by Israel Science Foundation grant number 541/17. D.K. is supported in part by a Department of Energy (DOE) Early Career award DE-SC0008067, a DOE Office of Nuclear Physics award DE-SC0017616, and a DOE SciDAC award DE-SC0018297, and by the Director, Office of Energy Research, Office of High Energy and Nuclear Physics, Divisions of Nuclear Physics, of the US Department of Energy under contract number DE-AC02-05CH11231. This research used resources of the National Energy Research Scientific Computing Center, a DOE Office of Science User Facility supported by the Office of Science of the US Department of Energy under contract number DE AC02-05CH11231. This research has made use of the NASA/IPAC Extragalactic Database, which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with NASA. The Digitized Sky Surveys were produced at the Space Telescope Science Institute (STScI) under US Government grant number NAG W-2166. The UK Schmidt Telescope was operated by the Royal Observatory Edinburgh, with funding from the UK Science and Engineering Research Council (later the UK Particle Physics and Astronomy Research Council), until June 1988, and thereafter by the Anglo-Australian Observatory. Supplementary funding for sky-survey work at the STScI is provided by the European Southern Observatory.

Author information


  1. Department of Physics, University of California, Santa Barbara, California 93106-9530, USA

    • Iair Arcavi
    • , Griffin Hosseinzadeh
    • , D. Andrew Howell
    • , Curtis McCully
    •  & Sergiy Vasylyev
  2. Las Cumbres Observatory, 6740 Cortona Drive, Suite 102, Goleta, California 93117-5575, USA

    • Iair Arcavi
    • , Griffin Hosseinzadeh
    • , D. Andrew Howell
    • , Curtis McCully
    •  & Sergiy Vasylyev
  3. School of Physics and Astronomy, Tel Aviv University, Tel Aviv 69978, Israel

    • Dovi Poznanski
    • , Michael Zaltzman
    •  & Dan Maoz
  4. Nuclear Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720-8169, USA

    • Daniel Kasen
  5. Departments of Physics and Astronomy, University of California, Berkeley, California 94720-7300, USA

    • Daniel Kasen
  6. Columbia Astrophysics Laboratory, Columbia University, New York, New York 10027, USA

    • Jennifer Barnes
  7. Department of Physics, University of California, 1 Shields Avenue, Davis, California 95616-5270, USA

    • Stefano Valenti


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I.A. is Principal Investigator of the LCO gravitational-wave follow-up program; he initiated and analysed the observations presented here and wrote the manuscript. G.H. helped with the LCO alert listener and ingestion pipeline, with follow-up observations and image analysis, and performed the blackbody fits. D.A.H. is the LCO–LIGO liaison, head of the LCO supernova group, and helped with the manuscript. C.M. assisted with obtaining and analysing data, and helped with the LCO alert listener. D.P. helped design the LCO follow-up program, assisted with the galaxy prioritization pipeline and contributed to the manuscript. D.K. and J.B. developed theoretical models and interpretations. M.Z. built the galaxy prioritization pipeline. S. Vasylyev built the LCO alert listener and ingestion pipeline. D.M. helped in discussions and with the manuscript. S. Valenti helped with image analysis and with the manuscript.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Iair Arcavi.

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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