Type Ia supernovae have been used empirically as ‘standard candles’ to demonstrate the acceleration of the expansion of the Universe1,2,3 even though fundamental details, such as the nature of their progenitor systems and how the stars explode, remain a mystery4,5,6. There is consensus that a white dwarf star explodes after accreting matter in a binary system, but the secondary body could be anything from a main-sequence star to a red giant, or even another white dwarf. This uncertainty stems from the fact that no recent type Ia supernova has been discovered close enough to Earth to detect the stars before explosion. Here we report early observations of supernova SN 2011fe in the galaxy M101 at a distance7 from Earth of 6.4 megaparsecs. We find that the exploding star was probably a carbon–oxygen white dwarf, and from the lack of an early shock we conclude that the companion was probably a main-sequence star. Early spectroscopy shows high-velocity oxygen that slows rapidly, on a timescale of hours, and extensive mixing of newly synthesized intermediate-mass elements in the outermost layers of the supernova. A companion paper8 uses pre-explosion images to rule out luminous red giants and most helium stars as companions to the progenitor.
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The PTF project is a scientific collaboration between the California Institute of Technology, Columbia University, Las Cumbres Observatory, the Lawrence Berkeley National Laboratory, the National Energy Research Scientific Computing Center, the University of Oxford and the Weizmann Institute of Science. The National Energy Research Scientific Computing Center, supported by the Office of Science of the US Department of Energy (DOE), provided staff, computational resources and data storage for this project. P.E.N. acknowledges support from the US DOE Scientific Discovery through Advanced Computing programme. M.S. acknowledges support from the Royal Society. J.S.B. and L.B. were supported by the National Science Foundation (NSF). The work of A.V.F. is funded by the NSF, the TABASGO Foundation, Gary and Cynthia Bengier, and the Richard and Rhoda Goldman Fund. A.G. thanks the ISF and BSF. The Liverpool Telescope is operated by Liverpool John Moores University in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias with financial support from the UK Science and Technology Facilities Council. Some of the data presented here were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and NASA; the observatory was made possible by the generous financial support of the W. M. Keck Foundation. We thank the staffs of the many observatories at which data were obtained for their assistance.
The authors declare no competing financial interests.
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Nugent, P., Sullivan, M., Cenko, S. et al. Supernova SN 2011fe from an exploding carbon–oxygen white dwarf star. Nature 480, 344–347 (2011). https://doi.org/10.1038/nature10644
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