A luminous quasar at a redshift of z = 7.085

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The intergalactic medium was not completely reionized until approximately a billion years after the Big Bang, as revealed1 by observations of quasars with redshifts of less than 6.5. It has been difficult to probe to higher redshifts, however, because quasars have historically been identified2,3,4 in optical surveys, which are insensitive to sources at redshifts exceeding 6.5. Here we report observations of a quasar (ULAS J112001.48+064124.3) at a redshift of 7.085, which is 0.77 billion years after the Big Bang. ULAS J1120+0641 has a luminosity of 6.3 × 1013L and hosts a black hole with a mass of 2 × 109M (where L and M are the luminosity and mass of the Sun). The measured radius of the ionized near zone around ULAS J1120+0641 is 1.9 megaparsecs, a factor of three smaller than is typical for quasars at redshifts between 6.0 and 6.4. The near-zone transmission profile is consistent with a Lyα damping wing5, suggesting that the neutral fraction of the intergalactic medium in front of ULAS J1120+0641 exceeded 0.1.

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M.P. acknowledges support from the University of London’s Perren Fund. P.C.H. and R.G.McM. acknowledge support from the STFC-funded Galaxy Formation and Evolution programme at the Institute of Astronomy. X. Fan and R. White supplied spectra of the SDSS quasars. M. Haehnelt provided insights into quasar near-zone physics. The staffs of the Joint Astronomy Centre, the Cambridge Astronomical Survey Unit and the Wide-Field Astronomy Unit, Edinburgh, all made vital contributions to the UKIDSS project. The support staff at the Gemini North Telescope, particularly K. Roth, provided assistance with the Gemini observations. This work is based in part on data obtained from UKIDSS, SDSS, the Liverpool Telescope, the Isaac Newton Telescope, the Gemini Observatory and the European Southern Observatory.

Author information


  1. Astrophysics Group, Imperial College London, Blackett Laboratory, Prince Consort Road, London SW7 2AZ, UK

    • Daniel J. Mortlock
    • , Stephen J. Warren
    •  & Mitesh Patel
  2. European Southern Observatory, 2 Karl-Schwarzschild Strasse, 85748 Garching bei München, Germany

    • Bram P. Venemans
  3. Institute of Astronomy, Madingley Road, Cambridge CB3 0HA, UK

    • Paul C. Hewett
    • , Richard G. McMahon
    • , Eduardo A. Gonzáles-Solares
    •  & Mike J. Irwin
  4. Astrophysics Research Institute, Liverpool John Moores University, Twelve Quays House, Egerton Wharf, Birkenhead CH41 1LD, UK

    • Chris Simpson
  5. Institute for Computational Cosmology, Department of Physics, University of Durham, South Road, Durham DH1 3LE, UK

    • Tom Theuns
  6. Universiteit Antwerpen, Campus Groenenborger, Groenenborgerlaan 171, B-2020 Antwerpen, Belgium

    • Tom Theuns
  7. Joint Astronomy Centre, 660 North A'oho¯ku¯ Place, Hilo, Hawaii 96720, USA

    • Andy Adamson
  8. School of Physics and Astronomy, University of Nottingham, University Park, Nottingham NG7 2RD, UK

    • Simon Dye
  9. Institute for Astronomy, SUPA (Scottish Universities Physics Alliance), University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ, UK

    • Nigel C. Hambly
    •  & Andy Lawrence
  10. Gemini Observatory, 670 North A'oho¯ku¯ Place, Hilo, Hawaii 96720, USA

    • Paul Hirst
  11. Leiden Observatory, Leiden University, PO Box 9513, NL-2300 RA Leiden, The Netherlands

    • Ernst Kuiper
    •  & Huub J. A. Röttgering


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D.J.M., S.J.W., M.P., B.P.V., P.C.H., R.G.McM. and C.S. identified ULAS J1120+0641 and obtained the follow-up observations. S.J.W., P.C.H., D.J.M., T.T., B.P.V., R.G.McM. and M.P. analysed the follow-up observations and interpreted the results. A.A., S.D., E.A.G.-S., N.C.H., P.H., M.J.I. and A.L. obtained, analysed and disseminated the UKIDSS data. E.K. and H.J.A.R. obtained the FORS2 spectrum of ULAS J1120+0641. D.J.M. and S.J.W. wrote the manuscript, into which all other authors had input.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Daniel J. Mortlock.