Abstract

Every supernova so far observed has been considered to be the terminal explosion of a star. Moreover, all supernovae with absorption lines in their spectra show those lines decreasing in velocity over time, as the ejecta expand and thin, revealing slower-moving material that was previously hidden. In addition, every supernova that exhibits the absorption lines of hydrogen has one main light-curve peak, or a plateau in luminosity, lasting approximately 100 days before declining1. Here we report observations of iPTF14hls, an event that has spectra identical to a hydrogen-rich core-collapse supernova, but characteristics that differ extensively from those of known supernovae. The light curve has at least five peaks and remains bright for more than 600 days; the absorption lines show little to no decrease in velocity; and the radius of the line-forming region is more than an order of magnitude bigger than the radius of the photosphere derived from the continuum emission. These characteristics are consistent with a shell of several tens of solar masses ejected by the progenitor star at supernova-level energies a few hundred days before a terminal explosion. Another possible eruption was recorded at the same position in 1954. Multiple energetic pre-supernova eruptions are expected to occur in stars of 95 to 130 solar masses, which experience the pulsational pair instability2,3,4,5. That model, however, does not account for the continued presence of hydrogen, or the energetics observed here. Another mechanism for the violent ejection of mass in massive stars may be required.

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Acknowledgements

I. Arcavi is an Einstein Fellow. B.S. is a Hubble Fellow and a Carnegie-Princeton Fellow. A.V.F. is a Miller Senior Fellow. See the Supplementary Information for a full list of Acknowledgements.

Author information

Affiliations

  1. Las Cumbres Observatory, Goleta, California 93117, USA

    • Iair Arcavi
    • , D. Andrew Howell
    • , Griffin Hosseinzadeh
    • , Curtis McCully
    • , Zheng Chuen Wong
    • , Sarah Rebekah Katz
    •  & David Guevel
  2. Kavli Institute for Theoretical Physics, University of California, Santa Barbara, California 93106, USA

    • Iair Arcavi
    •  & Lars Bildsten
  3. Department of Physics, University of California, Santa Barbara, California 93106, USA

    • Iair Arcavi
    • , D. Andrew Howell
    • , Lars Bildsten
    • , Griffin Hosseinzadeh
    • , Curtis McCully
    • , Zheng Chuen Wong
    • , Sarah Rebekah Katz
    •  & David Guevel
  4. Nuclear Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA

    • Daniel Kasen
  5. Department of Physics, University of California, Berkeley, California 94720, USA

    • Daniel Kasen
  6. Department of Astronomy, University of California, Berkeley, California 94720-3411, USA

    • Daniel Kasen
    • , Peter E. Nugent
    • , Melissa L. Graham
    • , Ken J. Shen
    •  & Alexei V. Filippenko
  7. Department of Particle Physics and Astrophysics, The Weizmann Institute of Science, Rehovot 76100, Israel

    • Avishay Gal-Yam
    • , Giorgos Leloudas
    • , Assaf Horesh
    • , Eran O. Ofek
    • , Ofer Yaron
    •  & Danny Khazov
  8. The Oskar Klein Centre, Department of Astronomy, Stockholm University, AlbaNova, SE-10691 Stockholm, Sweden

    • Jesper Sollerman
    • , Francesco Taddia
    • , Christoffer Fremling
    •  & Anders Nyholm
  9. Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, Juliane Maries vej 30, 2100 Copenhagen, Denmark

    • Giorgos Leloudas
    •  & Daniel A. Perley
  10. Computational Research Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA

    • Peter E. Nugent
  11. Racah Institute of Physics, The Hebrew University of Jerusalem, Jerusalem 91904, Israel

    • Assaf Horesh
    •  & Nir J. Shaviv
  12. Department of Physics, Astrophysics, University of Oxford, Denys Wilkinson Building, Oxford OX1 3RH, UK

    • Kunal Mooley
    •  & Rob Fender
  13. Astrophysics Group, Cavendish Laboratory, 19 J. J. Thomson Avenue, Cambridge CB3 0HE, UK

    • Clare Rumsey
  14. Astrophysics Science Division, NASA Goddard Space Flight Center, Code 661, Greenbelt, Maryland 20771, USA

    • S. Bradley Cenko
  15. Joint Space-Science Institute, University of Maryland, College Park, Maryland 20742, USA

    • S. Bradley Cenko
  16. Department of Astronomy, University of Washington, Box 351580, Seattle, Washington 98195-1580, USA

    • Melissa L. Graham
    •  & Yi Cao
  17. Astrophysics Research Institute, Liverpool John Moores University, IC2, Liverpool Science Park, 146 Brownlow Hill, Liverpool L3 5RF, UK

    • Daniel A. Perley
  18. The Raymond and Beverly Sackler School of Physics and Astronomy, Tel Aviv University, Tel Aviv 69978, Israel

    • Ehud Nakar
    •  & Omer Bromberg
  19. eScience Institute, University of Washington, Box 351570, Seattle, Washington 98195-1580, USA

    • Yi Cao
  20. Physics Department and Tsinghua Center for Astrophysics, Tsinghua University, Beijing 100084, China

    • Xiaofeng Wang
    • , Fang Huang
    • , Liming Rui
    • , Wenxiong Li
    •  & Zhitong Li
  21. Key Laboratory of Optical Astronomy, National Astronomical Observatories of China, Chinese Academy of Sciences, Beijing 100012, China

    • Tianmeng Zhang
  22. School of Astronomy and Space Science, University of Chinese Academy of Sciences, Beijing 101408, China

    • Tianmeng Zhang
  23. Yunnan Observatories, Chinese Academy of Sciences, Kunming 650011, China

    • Jujia Zhang
  24. Key Laboratory for the Structure and Evolution of Celestial Objects, Chinese Academy of Sciences, Phoenix Mountain, East District, Kunming, Yunnan 650216, China

    • Jujia Zhang
  25. Department of Physics, University of California, 1 Shields Avenue, Davis, California 95616, USA

    • Stefano Valenti
  26. Carnegie Observatories, 813 Santa Barbara Street, Pasadena, California 91101, USA

    • Benjamin Shappee
    •  & Nick Konidaris
  27. Department of Astronomy, The Ohio State University, 140 West 18th Avenue, Columbus, Ohio 43210, USA

    • Christopher S. Kochanek
    •  & Thomas W.-S. Holoien
  28. Center for Cosmology and AstroParticle Physics (CCAPP), The Ohio State University, 191 W. Woodruff Avenue, Columbus, Ohio 43210, USA

    • Christopher S. Kochanek
    •  & Thomas W.-S. Holoien
  29. Miller Institute for Basic Research in Science, University of California, Berkeley, California 94720, USA

    • Alexei V. Filippenko
  30. Cahill Center for Astrophysics, California Institute of Technology, Pasadena, California 91125, USA

    • Mansi M. Kasliwal
    • , Nadja Blagorodnova
    • , Richard S. Walters
    •  & Ragnhild Lunnan
  31. Department of Physics and Astronomy, University of Southampton, Southampton SO17 1BJ, UK

    • Mark Sullivan
  32. Centre for Astrophysics and Supercomputing, Swinburne University of Technology, PO Box 218, Victoria 3122, Australia

    • Igor Andreoni
  33. ARC Centre of Excellence for All-sky Astrophysics (CAASTRO), Australia

    • Igor Andreoni
  34. Australian Astronomical Observatory. PO Box 915, North Ryde, New South Wales 1670, Australia

    • Igor Andreoni
  35. Spitzer Science Center, California Institute of Technology, MS 314-6, Pasadena, California 91125, USA

    • Russ R. Laher
  36. Space and Atmospheric Sciences Group, Mail Stop D466, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA

    • Przemek Wozniak
  37. Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California 91109, USA

    • Brian Bue

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Contributions

I. Arcavi initiated the study, triggered follow-up observations, reduced data, performed the analysis and wrote the manuscript. D.A.H. is the Principal Investigator of the Las Cumbres Observatory (LCO) Supernova Key Project through which all of the LCO data were obtained; he also assisted with interpretation and the manuscript. D. Kasen and L.B. assisted with theoretical models, data interpretation, and with the manuscript. G.H. and C.McC. assisted with obtaining and reducing LCO data. Z.C.W. first flagged the supernova as interesting. S.R.K. performed the spectral expansion velocity measurements. A.G.-Y. is the Principal Investigator for core-collapse supernovae in iPTF and assisted with interpretation. J.S. and F.T. obtained the Nordic Optical Telescope spectra and polarimetry data and assisted with the manuscript. G.L. reduced the polarimetry data. C.F. reduced the Palomar 60-inch telescope (P60) data. P.E.N. discovered the 1954 eruption image of iPTF14hls, helped obtain the host-galaxy spectrum, and is a Co-Principal Investigator of the Keck proposal under which it and one of the supernova spectra were obtained. A.H. obtained and reduced the Very Large Array (VLA) data and is Principal Investigator of the programme through which the data were obtained. K.M. and C.R. obtained and reduced the Arcminute Microkelvin Imager Large Array (AMI-LA) data. S.B.C. obtained and reduced the Swift X-Ray Telescope (XRT) data. M.L.G. obtained and reduced Keck spectra. D.A.P. performed the host-galaxy analysis and assisted with the manuscript. E.N., O.B., N.J.S. and K.J.S. assisted with theoretical interpretation and the manuscript. E.O.O. helped with interpretation and the manuscript. Y.C. built the real-time iPTF image-subtraction pipeline and obtained Palomar 200-inch telescope (P200) observations. X.W., F.H., L.R., T.Z., W.L., Z.L. and J.Z. obtained and reduced the Xinglong, Lijiang, and Tsinghua University-NAOC telescope (TNT) data. S.V. built the LCO photometric and spectroscopic reduction pipelines and assisted with LCO observations, interpretation, and the manuscript. D.G. assisted with the Palomar Observatory Sky Survey (POSS) image analysis. B.S., C.S.K. and T.W.-S.H. obtained and reduced the All Sky Automated Survey for Supernovae (ASAS-SN) pre-discovery limits. A.V.F. is a Co-Principal Investigator of the Keck proposal under which the host-galaxy spectrum and one of the supernova spectra were obtained; he also helped with the manuscript. R.F. is Principal Investigator of the programme through which the AMI-LA data were obtained. A.N. helped scan for iPTF candidates and assisted with the manuscript. O.Y. is in charge of the iPTF candidate scanning effort. M.M.K. led the work for building iPTF. M.S. wrote the pipeline used to reduce Palomar 48-inch Oschin Schmidt telescope (P48) data. N.B. and R.S.W. obtained P60 SEDM photometry. R.L., D. Khazov, and I. Andreoni obtained P200 observations. R.R.L. contributed to building the P48 image-processing pipeline. N.K. was a main builder of the P60 SEDM. P.W. and B.B. helped build the machine-learning algorithms that identify iPTF supernova candidates.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Iair Arcavi.

Reviewer Information Nature thanks P. Mazzali, S. Woosley and the other anonymous reviewer(s) for their contribution to the peer review of this work.

Publisher's note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

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    Supplementary Information

    This file contains the full list of acknowledgements.