Artist’s impression of cold intergalactic rain
Artist’s impression of cold intergalactic rain
Composite image of Abell 2597 Brightest Cluster Galaxy
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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 centre of a huge galaxy one billion
light-years from Earth. The results will appear in the journal Nature on
9 June 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 ionised gas from the galaxy’s halo.
The new ALMA observations show 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.
“Although it has been a major theoretical prediction in
recent years, 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, former ESO Fellow, 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 the 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 massive elliptical galaxy, descriptively named the
Abell 2597 Brightest Cluster Galaxy. Suffusing the space between these
galaxies is a diffuse atmosphere of hot ionised gas, 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."
Near the centre of this galaxy the researchers discovered
just this scenario: three massive clumps of cold gas are careening
toward the supermassive black hole in the galaxy’s core at about a
million kilometres per hour. 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 [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, essentially teetering on the
edge of being devoured, in astronomical terms.
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 for a long time.
The astronomers now plan to use ALMA to search for these
"rainstorms" in other galaxies in order to determine whether such cosmic
weather is as common as current theory suggests it might be.
Notes
[1] The shadows are formed when the in-falling opaque gas clouds block
out a portion of the bright background millimetre-wavelength light
emitted by electrons spiraIling around magnetic fields very near the
central supermassive black hole.
More Information
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.
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”.
Links
Contacts
Grant Tremblay
Yale University
New Haven, Connecticut, USA
Tel: +1 207 504 4862
Email: grant.tremblay@yale.edu
Francoise Combes
LERMA, Paris Observatory
France
Email: francoise.combes@obspm.fr
Richard Hook
ESO Public Information Officer
Garching bei München, Germany
Tel: +49 89 3200 6655
Cell: +49 151 1537 3591
Email: rhook@eso.org
Source: ESO
