Nearly a century ago it was recognized1 that radiation absorption by stellar matter controls the internal temperature profiles within stars. Laboratory opacity measurements, however, have never been performed at stellar interior conditions, introducing uncertainties in stellar models2,3,4,5. A particular problem arose2,3,6,7,8 when refined photosphere spectral analysis9,10 led to reductions of 30–50 per cent in the inferred amounts of carbon, nitrogen and oxygen in the Sun. Standard solar models11 using the revised element abundances disagree with helioseismic observations that determine the internal solar structure using acoustic oscillations. This could be resolved if the true mean opacity for the solar interior matter were roughly 15 per cent higher than predicted2,3,6,7,8, because increased opacity compensates for the decreased element abundances. Iron accounts for a quarter of the total opacity2,12 at the solar radiation/convection zone boundary. Here we report measurements of wavelength-resolved iron opacity at electron temperatures of 1.9–2.3 million kelvin and electron densities of (0.7–4.0) × 1022 per cubic centimetre, conditions very similar to those in the solar region that affects the discrepancy the most: the radiation/convection zone boundary. The measured wavelength-dependent opacity is 30–400 per cent higher than predicted. This represents roughly half the change in the mean opacity needed to resolve the solar discrepancy, even though iron is only one of many elements that contribute to opacity.

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Sandia is a multiprogramme laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under contract DE-AC04-94AL85000. The Los Alamos National Laboratory is operated by Los Alamos National Security, LLC, for the NNSA of the US DOE under contract number DE-AC5206NA25396. J.E.B. acknowledges support from a DOE High Energy Density Laboratory Plasmas grant. A.K.P. and C.O. also acknowledge support from a DOE High Energy Density Laboratory Plasmas grant. We appreciate the efforts of the entire Z facility team. We thank S. Turck-Chièze, H. Morris, and M. Pinsonneault for discussions. We also thank R. W. Lee for critiquing the manuscript. We appreciate support for the experiments provided by R. J. Leeper, J. L. Porter, M. K. Matzen and M. Herrmann.

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  1. Sandia National Laboratories, 1515 Eubank SE, Albuquerque, New Mexico 87185-1196, USA

    • J. E. Bailey
    • , T. Nagayama
    • , G. P. Loisel
    • , G. A. Rochau
    •  & S. B. Hansen
  2. Commissariat à l’Énergie Atomique (CEA) et aux Énergies Alternatives, F-91297 Arpajon, France

    • C. Blancard
    • , Ph. Cosse
    • , G. Faussurier
    • , F. Gilleron
    •  & J.-C. Pain
  3. Los Alamos National Laboratory, Bikini Atoll Road, Los Alamos, New Mexico 87545, USA

    • J. Colgan
    • , C. J. Fontes
    • , D. P. Kilcrease
    •  & M. Sherrill
  4. Prism Computational Sciences, 455 Science Drive, Suite 140, Madison, Wisconsin 53711, USA

    • I. Golovkin
    •  & J. J. MacFarlane
  5. Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, California 94550-9234, USA

    • C. A. Iglesias
    •  & B. G. Wilson
  6. University of Nevada, 1664 North Virginia Street, Reno, Nevada 89557, USA

    • R. C. Mancini
  7. Ohio State University, 140 West 18th Avenue, Columbus, Ohio 43210, USA

    • S. N. Nahar
    • , C. Orban
    •  & A. K. Pradhan


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These measurements were conceived and planned by J.E.B. and G.A.R. J.E.B. was the primary author of the manuscript, with important contributions from T.N. Experiments were conducted by J.E.B., G.A.R. and G.P.L. The Z-facility data were analysed by T.N., J.E.B. and G.P.L., with assistance from G.A.R., C.A.I., B.G.W., I.G., J.J. M. and R.C.M. OPAS calculations were performed by C.B., G.F. and Ph.C. ATOMIC calculations were performed by J.C., with assistance from C.F., D.P.K. and M.S. SCRAM calculations were provided by S.B.H. SCO calculations were performed by J.-C.P. and F.G. OP calculations were performed by C.O., with assistance from A.K.P. and S.N.N. All authors discussed the results, commented on the manuscript, and contributed to the interpretation.

Competing interests

The authors declare no competing financial interests.

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Correspondence to J. E. Bailey.

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