Cold, clumpy accretion onto an active supermassive black hole.
Supermassive black holes in galaxy centres can grow by the accretion of gas, liberating energy that might regulate star formation on galaxy-wide scales. 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 gas. Recent theory and simulations 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 plasma. Under the right conditions, thermal instabilities produce a rain of cold clouds that fall towards the galaxy's centre, sustaining star formation amid a kiloparsec-scale molecular nebula that is found at its core. 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 observations of warmer atomic gas at extremely high spatial resolution, 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.
Yale Center for Astronomy and Astrophysics, Yale University, 52 Hillhouse Avenue, New Haven, Connecticut 06511, USA.|European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching bei München, Germany.
Grant R
GR
Tremblay
ASTRON, Netherlands Institute for Radio Astronomy, PO Box 2, 7990 AA Dwingeloo, The Netherlands.|Leiden Observatory, Leiden University, Niels Borhweg 2, NL-2333 CA Leiden, The Netherlands.
J B Raymond
JB
Oonk
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
F
Combes
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.
Philippe
P
Salomé
Department of Physics and Astronomy, University of Manitoba, Winnipeg, Manitoba R3T 2N2, Canada.|School of Physics and Astronomy, Rochester Institute of Technology, 84 Lomb Memorial Drive, Rochester, New York 14623, USA.
Christopher  P
C
O'Dea
Department of Physics and Astronomy, University of Manitoba, Winnipeg, Manitoba R3T 2N2, Canada.|Chester F. Carlson Center for Imaging Science, Rochester Institute of Technology, 84 Lomb Memorial Drive, Rochester, New York 14623, USA.
Stefi A
SA
Baum
Physics and Astronomy Department, Michigan State University, East Lansing, Michigan 48824-2320, USA.
G Mark
GM
Voit
Physics and Astronomy Department, Michigan State University, East Lansing, Michigan 48824-2320, USA.
Megan
M
Donahue
Physics and Astronomy Department, Waterloo University, 200 University Avenue West, Waterloo, Ontario N2L 2GL, Canada.
Brian R
BR
McNamara
European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching bei München, Germany.|School of Physics and Astronomy, Cardiff University, The Parade, Cardiff CF24 3AA, UK.
Timothy A
TA
Davis
Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA.
Michael A
MA
McDonald
Department of Physics, Durham University, Durham DHL 3LE, UK.
Alastair C
AC
Edge
Naval Research Laboratory Remote Sensing Division, Code 7213, 4555 Overlook Avenue Southwest, Washington DC 20375, USA.
Tracy E
TE
Clarke
European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching bei München, Germany.|Instituto de Radioastronomía y Astrofísica, UNAM, Apartado Postal 3-72 (Xangari), 58089 Morelia, Michoacán, Mexico.
Roberto
R
Galván-Madrid
H. W. Wills Physics Laboratory, University of Bristol, Tyndall Avenue, Bristol BS8 1TL, UK.
Malcolm N
MN
Bremer
Yale Center for Astronomy and Astrophysics, Yale University, 52 Hillhouse Avenue, New Haven, Connecticut 06511, USA.
Louise O V
LO
Edwards
Institute of Astronomy, Cambridge University, Madingly Road, Cambridge CB3 0HA, UK.
Andrew C
AC
Fabian
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.
Stephen
S
Hamer
Department of Astronomy, University of Michigan, 1085 South University Avenue, Ann Arbor, Michigan 48109, USA.
Yuan
Y
Li
Laboratoire AIM-Paris-Saclay, CEA/DSM/Irfu CNRS-Université Paris Diderot, CE-Saclay, F-91191 Gif-sur-Yvette, France.
Anaëlle
A
Maury
Institute of Astronomy, Cambridge University, Madingly Road, Cambridge CB3 0HA, UK.
Helen R
HR
Russell
Department of Physics and Astronomy, University of Rochester, Rochester, New York 14627, USA.
Alice C
AC
Quillen
Yale Center for Astronomy and Astrophysics, Yale University, 52 Hillhouse Avenue, New Haven, Connecticut 06511, USA.
C Megan
CM
Urry
Max-Planck-Institut für Extraterrestrische Physik, 85748 Garching bei München, Germany.
Jeremy S
JS
Sanders
ASTRON, Netherlands Institute for Radio Astronomy, PO Box 2, 7990 AA Dwingeloo, The Netherlands.
Michael W
MW
Wise