|ALMA Witness Intergalactic Deluge Feeding a Black Hole||
Wednesday, 08 June 2016
An international team of astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA) has witnessed a cosmic weather event that has never been seen before – a cluster of towering intergalactic gas clouds raining in on the supermassive black hole at the center of a huge galaxy one billion light-years from Earth. The results will appear in the journal Nature on June 9, 2016.
The new ALMA observation is the first direct evidence that cold dense clouds can coalesce out of hot intergalactic gas and plunge into the heart of a galaxy to feed its central supermassive black hole. It also reshapes astronomers’ views on how supermassive black holes feed, in a process known as accretion.
Previously, astronomers believed that, in the largest galaxies, supermassive black holes fed on a slow and steady diet of hot ionized gas from the galaxy’s halo. The new ALMA observation shows that, when the intergalactic weather conditions are right, black holes can also gorge on a clumpy, chaotic downpour of giant clouds of very cold molecular gas.
"This so-called cold, chaotic accretion has been a major theoretical prediction in recent years, but this is one of the first unambiguous pieces of observational evidence for a chaotic, cold 'rain' feeding a supermassive black hole," said Grant Tremblay, an astronomer with Yale University in New Haven, Connecticut, USA and lead author on the new paper. "It's exciting to think we might actually be observing this galaxy-spanning ‘rainstorm’ feeding a black hole whose mass is about 300 million times that of our Sun."
Tremblay and his team used ALMA to peer into an unusually bright cluster of about 50 galaxies, collectively known as Abell 2597. At its core is a singular massive elliptical galaxy, descriptively named the Abell 2597 Brightest Cluster Galaxy. Spreading over the space between these galaxies is a diffuse atmosphere of hot, ionized plasma, which was previously observed with NASA’s Chandra X-ray Observatory.
"This very, very hot gas can quickly cool, condense, and precipitate in much the same way that warm, humid air in Earth's atmosphere can spawn rain clouds and precipitation," Tremblay said. "The newly condensed clouds then rain in on the galaxy, fueling star formation and feeding its supermassive black hole."
The cosmic weather report, as illustrated in this artist concept, calls for condensing clouds of cold molecular gas around the Abell 2597 Brightest Cluster Galaxy. The clouds condense out of the hot, ionized gas that suffuses the space between the galaxies in this cluster. New ALMA data show that these clouds are raining in on the galaxy, plunging toward the supermassive black hole at its center. Credit: NRAO/AUI/NSF; Dana Berry / SkyWorks; ALMA (ESO/NAOJ/NRAO) | Download image
Near the center of this galaxy, the researchers discovered this exact scenario: three massive clumps of cold gas careening toward the supermassive black hole in the galaxy’s core at 300 kilometers per second, at about a million kilometers. 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 the billion light-year-long "shadows" they cast toward Earth. These shadows, known as absorption features, were formed by the in-falling gas clouds blocking out a portion of the bright background millimeter-wavelength light emitted by electrons spiraling around magnetic fields very near the central supermassive black hole.
Deep in the heart of the Abell 2597 Brightest Cluster Galaxy, astronomers see a small cluster of giant gas clouds raining in on the central black hole. They were revealed by the billion light-year-long shadows they cast toward Earth. These ALMA data present the first observational evidence for predicted "chaotic, cold" accretion on a supermassive black hole. Credit: NRAO/AUI/NSF; Dana Berry / SkyWorks; ALMA (ESO/NAOJ/NRAO) | Download image
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, essentially teetering on the edge of being devoured, in astronomical terms.
Composite image of Abell 2597 Brightest Cluster Galaxy. The background image (blue) is from the Hubble Space Telescope. The foreground (red) is ALMA data showing the distribution of carbon monoxide gas in and around the galaxy. The pull-out box is the ALMA data of the "shadow" (black) produced by absorption of the millimeter-wavelength light emitted by electrons whizzing around powerful magnetic fields generated by the galaxy's supermassive black hole. The shadow indicates that cold clouds of molecular gas are raining in on the black hole. Credit: B. Saxton (NRAO/AUI/NSF); G. Tremblay et al.; NASA/ESA Hubble; ALMA (ESO/NAOJ/NRAO) | Download image
While ALMA was only able to detect three clouds of cold gas near the black hole, the astronomers speculate that there may be thousands like them in the vicinity, setting up the black hole for a continuing downpour that could fuel its activity well into the future.
The astronomers now plan to use ALMA in a broader search for these "rainstorms" in other galaxies in order to determine if such cosmic weather is as common as current theory suggests it might be.
The cosmic weather report, as illustrated in this artist’s concept video, calls for condensing clouds of cold molecular gas around the Abell 2597 Brightest Cluster Galaxy. The clouds condense out of the hot, ionised gas that suffuses the space between the galaxies in this cluster. New ALMA data show that these clouds are raining in on the galaxy, plunging toward the supermassive black hole at its centre. Credit: NRAO/AUI/NSF; Dana Berry/SkyWorks; ALMA (ESO/NAOJ/NRAO). Music: Johan B. Monell | Download video
This research was presented in a paper entitled “Cold, clumpy accretion onto an active supermassive black hole”, by Grant R. Tremblay et al., to appear in the journal Nature on 9 June 2016. on 9 June 2016.
The research paper can be downloaded here.
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, Michoacán, México; 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 the European Organisation for Astronomical Research in the Southern Hemisphere (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.
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