‘Shadows’ cast by molecular clouds moving toward the supermassive black hole. imprinting absorption lines on the continuum-subtracted spectrum from the region around the core of the galaxy.

Cold gas cloud shadows in the glare of a supermassive black hole

An international team of astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA) has detected a cluster of cold molecular gas clouds only a few hundred lightyears from a supermassive black hole and falling toward it at a million kilometres per hour.  This new ALMA observation provides evidence that dense clouds can coalesce out of hot intergalactic gas and fall to the core of a galaxy to feed the supermassive black hole at its centre.  The results will appear in the journal Nature on 9 June 2016.

Lead author Grant Tremblay and his team used ALMA to peer into an unusually bright cluster of about 50 galaxies, collectively known as Abell 2597, which are one billion light-years from Earth.  At its core is a massive elliptical galaxy - the brightest cluster galaxy. Suffusing the space between these galaxies is a diffuse atmosphere of hot, ionised plasma, which was previously observed with NASA’s Chandra X-ray Observatory.

Near the central galaxy in Abell 2597, the researchers discovered three massive clumps of cold gas falling toward the supermassive black hole at the galaxy’s centre.  Each cloud contains as much material as a million Suns and is tens of light-years across.  Normally, objects on that scale would be difficult to distinguish at these cosmic distances, even with ALMA’s amazing resolution. They were revealed, however, by their absorption of background light, which creates “shadows” in the observed spectrum[1].

Additional data from the National Science Foundation’s Very Long Baseline Array indicate that the gas clouds observed by ALMA are only about 300 light-years from the central black hole and could fuel radio-jet outbursts.  While ALMA was only able to detect three clouds of cold gas near the black hole, the astronomers speculate that there may be part of a larger ordered inflow that is steadily fuelling the supermassive black hole activity.

The astronomers now plan to use ALMA to search for these cold clouds in other galaxies in order to determine how the supermassive black hole activity can be dictated by rapidly cooling inflows from the surrounding gas atmosphere.

Notes
[1] The shadows, known as absorption features, are formed when the in-falling gas clouds block out a portion of the bright background millimetre-wavelength light emitted by electrons spiraling around magnetic fields very near the central supermassive black hole.

More Information
This research was presented in a paper entitled “Cold, clumpy accretion toward an active supermassive black hole”, by Grant R. Tremblay et al., to appear in the journal Nature on 9 June 2016.

Local contacts:

Dr Helen Russell & Prof Andy Fabian, Institute of Astronomy, Cambridge University

Figures:

Composite wavelength view of the A2597 cluster of galaxies: X-rays (blue); Radio (red) and Visible (yellow).

Credit: X-ray: NASA/CXC/Michigan State Univ/G.Voit et al; Optical: NASA/STScI & DSS; H-alpha: Carnegie Obs./Magellan/W.Baade Telescope/U.Maryland/M.McDonald

Composite wavelength view of the core of the A2597 cluster of galaxies: molecular gas detected by ALMA (red) superposed on the visible HST image.

The team is composed of Grant R. Tremblay (Yale University, New Haven, Connecticut, USA; ESO, Garching, Germany), J. B. Raymond Oonk (ASTRON, Netherlands Institute for Radio Astronomy, Dwingeloo, the Netherlands; Leiden Observatory, Leiden University, Leiden, the Netherlands), Françoise Combes (LERMA, Observatoire de Paris, PSL Research University, College de France, CNRS, Sorbonne University, Paris, France), Philippe Salomé (LERMA, Observatoire de Paris, PSL Research University, College de France, CNRS, Sorbonne University, Paris, France), Christopher O’Dea (University of Manitoba, Winnipeg, Canada; Rochester Institute of Technology, Rochester, New York, USA), Stefi A. Baum (University of Manitoba, Winnipeg, Canada; Rochester Institute of Technology, Rochester, New York, USA), G. Mark Voit (Michigan State University, East Lansing, Michigan, USA), Megan Donahue (Michigan State University, East Lansing, Michigan, USA), Brian R. McNamara (Waterloo University, Waterloo, Ontario, Canada), Timothy A. Davis (Cardiff University, Cardiff, United Kingdom; ESO, Garching, Germany), Michael A. McDonald (Kavli Institute for Astrophysics & Space Research, MIT, Cambridge, Massachusetts, USA), Alastair C. Edge (Durham University, Durham, United Kingdom), Tracy E. Clarke (Naval Research Laboratory Remote Sensing Division, Washington DC, USA), Roberto Galván-Madrid (Instituto de Radioastronomía y Astrofísica, UNAM, Morelia, Michoacan, Mexico; ESO, Garching, Germany), Malcolm N. Bremer (University of Bristol, Bristol, United Kingdom), Louise O. V. Edwards (Yale University, New Haven, Connecticut, USA), Andrew C. Fabian (Institute of Astronomy, Cambridge University, Cambridge, United Kingdom), Stephen Hamer (LERMA, Observatoire de Paris, PSL Research University, College de France, CNRS, Sorbonne University, Paris, France) , Yuan Li (University of Michigan, Ann Arbor, Michigan, USA ), Anaëlle Maury (Laboratoire AIMParis-Saclay, CEA/DSM/Irfu CNRS, University Paris Diderot, CE-Saclay, Gif-sur-Yvette, France), Helen Russell (Institute of Astronomy, Cambridge University, Cambridge, United Kingdom), Alice C. Quillen (University of Rochester, Rochester, New York, USA), C. Megan Urry (Yale University, New Haven, Connecticut, USA), Jeremy S. Sanders (Max-Planck-Institut für extraterrestrische Physik, Garching bei München, Germany), and Michael Wise (ASTRON, Netherlands Institute for Radio Astronomy, Dwingeloo, the Netherlands).

The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership of ESO, the U.S. National Science Foundation (NSF) and the National Institutes of Natural Sciences (NINS) of Japan in cooperation with the Republic of Chile. ALMA is funded by ESO on behalf of its Member States, by NSF in cooperation with the National Research Council of Canada (NRC) and the National Science Council of Taiwan (NSC) and by NINS in cooperation with the Academia Sinica (AS) in Taiwan and the Korea Astronomy and Space Science Institute (KASI).
ALMA construction and operations are led by ESO on behalf of its Member States; by the National Radio Astronomy Observatory (NRAO), managed by Associated Universities, Inc. (AUI), on behalf of North America; and by the National Astronomical Observatory of Japan (NAOJ) on behalf of East Asia. The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning and operation of ALMA.

ESO is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive ground-based astronomical observatory by far. It is supported by 16 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the United Kingdom, along with the host state of Chile. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world’s most advanced visible-light astronomical observatory and two survey telescopes. VISTA works in the infrared and is the world’s largest survey telescope and the VLT Survey Telescope is the largest telescope designed to exclusively survey the skies in visible light. ESO is a major partner in ALMA, the largest astronomical project in existence. And on Cerro Armazones, close to Paranal, ESO is building the 39-metre European Extremely Large Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.