Supermassive black holes in galaxy centres can grow by the accretion of gas, liberating energy that might regulate star formation on galaxy-wide scales1,2,3. The nature of the gaseous fuel reservoirs that power black hole growth is nevertheless largely unconstrained by observations, and is instead routinely simplified as a smooth, spherical inflow of very hot gas4. Recent theory5,6,7 and simulations8,9,10 instead predict that accretion can be dominated by a stochastic, clumpy distribution of very cold molecular clouds—a departure from the ‘hot mode’ accretion model—although unambiguous observational support for this prediction remains elusive. Here we report observations that reveal a cold, clumpy accretion flow towards a supermassive black hole fuel reservoir in the nucleus of the Abell 2597 Brightest Cluster Galaxy (BCG), a nearby (redshift z = 0.0821) giant elliptical galaxy surrounded by a dense halo of hot plasma11,12,13. Under the right conditions, thermal instabilities produce a rain of cold clouds that fall towards the galaxy’s centre14, sustaining star formation amid a kiloparsec-scale molecular nebula that is found at its core15. The observations show that these cold clouds also fuel black hole accretion, revealing ‘shadows’ cast by the molecular clouds as they move inward at about 300 kilometres per second towards the active supermassive black hole, which serves as a bright backlight. Corroborating evidence from prior observations16 of warmer atomic gas at extremely high spatial resolution17, along with simple arguments based on geometry and probability, indicate that these clouds are within the innermost hundred parsecs of the black hole, and falling closer towards it.

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ALMA is a partnership of ESO (representing its member states), NSF (USA) and NINS (Japan), together with NRC (Canada) and NSC and ASIAA (Taiwan), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by ESO, AUI/NRAO and NAOJ. We are grateful to the European ALMA Regional Centres, particularly those in Garching and Manchester, for their dedicated end-to-end support of data associated with this paper. We thank R. Larson for discussions. G.R.T. acknowledges support from National Aeronautics and Space Administration (NASA) through Einstein Postdoctoral Fellowship Award Number PF-150128, issued by the Chandra X-ray Observatory Center, which is operated by the Smithsonian Astrophysical Observatory for and on behalf of NASA under contract NAS8-03060. F.C. acknowledges the European Research Council (ERC) for the Advanced Grant Program no. 267399-Momentum. B.R.M. is supported by a grant from the Natural Sciences and Engineering Research Council of Canada. T.A.D. acknowledges support from a Science and Technology Facilities Council (STFC) Ernest Rutherford Fellowship. A.C.E. acknowledges support from STFC grant ST/L00075X/1. A.C.F. and H.R.R. acknowledge support from ERC Advanced Grant Program no. 340442-Feedback. M.N.B. acknowledges funding from the STFC. Basic research in radio astronomy at the Naval Research Laboratory is supported by 6.1 Base funding.

Author information


  1. Yale Center for Astronomy and Astrophysics, Yale University, 52 Hillhouse Avenue, New Haven, Connecticut 06511, USA

    • Grant R. Tremblay
    • , Louise O. V. Edwards
    •  & C. Megan Urry
  2. European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching bei München, Germany

    • Grant R. Tremblay
    • , Timothy A. Davis
    •  & Roberto Galván-Madrid
  3. ASTRON, Netherlands Institute for Radio Astronomy, PO Box 2, 7990 AA Dwingeloo, The Netherlands

    • J. B. Raymond Oonk
    •  & Michael W. Wise
  4. Leiden Observatory, Leiden University, Niels Borhweg 2, NL-2333 CA Leiden, The Netherlands

    • J. B. Raymond Oonk
  5. Laboratory for Studies of Radiation and Matter in Astrophysics and Atmospheres (LERMA), Observatoire de Paris, PSL Research University, College de France, CNRS, Sorbonne University, Paris, France

    • Françoise Combes
    • , Philippe Salomé
    •  & Stephen Hamer
  6. Department of Physics and Astronomy, University of Manitoba, Winnipeg, Manitoba R3T 2N2, Canada

    • Christopher P. O’Dea
    •  & Stefi A. Baum
  7. School of Physics and Astronomy, Rochester Institute of Technology, 84 Lomb Memorial Drive, Rochester, New York 14623, USA

    • Christopher P. O’Dea
  8. Chester F. Carlson Center for Imaging Science, Rochester Institute of Technology, 84 Lomb Memorial Drive, Rochester, New York 14623, USA

    • Stefi A. Baum
  9. Physics and Astronomy Department, Michigan State University, East Lansing, Michigan 48824-2320, USA

    • G. Mark Voit
    •  & Megan Donahue
  10. Physics and Astronomy Department, Waterloo University, 200 University Avenue West, Waterloo, Ontario N2L 2GL, Canada

    • Brian R. McNamara
  11. School of Physics and Astronomy, Cardiff University, The Parade, Cardiff CF24 3AA, UK

    • Timothy A. Davis
  12. Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA

    • Michael A. McDonald
  13. Department of Physics, Durham University, Durham DHL 3LE, UK

    • Alastair C. Edge
  14. Naval Research Laboratory Remote Sensing Division, Code 7213, 4555 Overlook Avenue Southwest, Washington DC 20375, USA

    • Tracy E. Clarke
  15. Instituto de Radioastronomía y Astrofísica, UNAM, Apartado Postal 3-72 (Xangari), 58089 Morelia, Michoacán, Mexico

    • Roberto Galván-Madrid
  16. H. W. Wills Physics Laboratory, University of Bristol, Tyndall Avenue, Bristol BS8 1TL, UK

    • Malcolm N. Bremer
  17. Institute of Astronomy, Cambridge University, Madingly Road, Cambridge CB3 0HA, UK

    • Andrew C. Fabian
    •  & Helen R. Russell
  18. Department of Astronomy, University of Michigan, 1085 South University Avenue, Ann Arbor, Michigan 48109, USA

    • Yuan Li
  19. Laboratoire AIM-Paris-Saclay, CEA/DSM/Irfu CNRS—Université Paris Diderot, CE-Saclay, F-91191 Gif-sur-Yvette, France

    • Anaëlle Maury
  20. Department of Physics and Astronomy, University of Rochester, Rochester, New York 14627, USA

    • Alice C. Quillen
  21. Max-Planck-Institut für Extraterrestrische Physik, 85748 Garching bei München, Germany

    • Jeremy S. Sanders


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G.R.T. was principal investigator on the original proposal, performed the data analysis, and wrote the paper. J.B.R.O., T.A.D., R.G.M. and A.M. were substantially involved in planning both scientific and technical aspects of the proposal, while T.A.D. and R.G.M. contributed ALMA data reduction and analysis expertise once the data were obtained. J.B.R.O., F.C. and P.S. invested substantial time in analysis of the data. Substantial scientific feedback was also provided over many months by F.C., J.B.R.O., C.P.O., S.A.B., G.M.V., M.D., B.R.M., M.A.M., T.E.C., H.R., A.C.E. and A.C.F., while all other co-authors discussed the results and commented on the manuscript.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Grant R. Tremblay.

This paper makes use of the following ALMA data: ADS/JAO.ALMA#2012.1.00988.S.

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