Feb 19, 2014 |
Clouds seen circling supermassive black hole (w/video)
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(Nanowerk News) Astronomers see huge clouds of gas orbiting supermassive black holes at the centres of galaxies. Once thought to be a relatively uniform, fog-like ring, the accreting matter instead forms clumps dense enough to intermittently dim the intense radiation blazing forth as these enormous objects condense and consume matter.
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Artist's concept of a supermassive black hole at the centre of a galaxy. (Image: NASA / JPL / Caltech)
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The international team reports their sightings in a paper to be published in the Monthly Notices of the Royal Astronomical Society ("First X-ray-based statistical tests for clumpy-torus models: eclipse events from 230 years of monitoring of Seyfert AGN"), available online now.
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Evidence for the clouds comes from records collected over 16 years by NASA's Rossi X-ray Timing Explorer, a satellite in low-earth orbit equipped with instruments that measured variations in X-ray sources. Those sources include active galactic nuclei, brilliantly luminous objects powered by supermassive black holes as they gather and condense huge quantities of dust and gas.
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By sifting through records for 55 active galactic nuclei Alex Markowitz, an astrophysicist at the University of California, San Diego and the Karl Remeis Observatory in Bamberg, Germany and colleagues found a dozen instances when the X-ray signal dimmed for periods of time ranging from hours to years, presumably when a cloud of dense gas passed between the source and satellite.
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Conceptual animation of the findings from the paper by A. Markowitz (UC San Diego & KRO/ECAP/FAU), M. Krumpe (ESO) and R. Nikutta (Univ. Andrés Bello) published in Monthly Notices of the Royal Astronomical Society. Animation by Wolfgang Steffen (UNAM, Ensenada, Mexico).
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Mirko Krumpe of the European Southern Observatory in Garching, Germany and Robert Nikutta, of Andrés Bello University in Santiago, Chile co-authored the report, which confirms what recent models of these systems have predicted.
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The clouds they observed orbit a few light-weeks to a few light-years from the centre of the active galactic nuclei. One, in a spiral galaxy in the direction of the constellation Centaurus designated NGC 3783, appeared to be in the midst of being torn apart by tidal forces.
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Support for this research came from NASA's Astrophysics Data Analysis Program (NNX11AD07G) and the European Community's Seventh Framework Program (229517). Nikutta acknowledges support from ALMA-CONICYT (31110001). Video produced by the Scientific Visualization Studio, Goddard Spaceflight Centre, NASA, based in part on visualisations created by Wolfgang Steffen, Institute of Astronomy, National Autonomous University of Mexico.
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