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Clouds circling supermassive black holes

Last Updated on Wednesday, 19 February 2014 17:25
Published on Wednesday, 19 February 2014 16:00

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.

Supermassiveblackhole nasajplArtist's concept of a supermassive black hole at the centre of a galaxy. Credit: NASA / JPL / CaltechThe international team reports their sightings in a paper to be published in the Monthly Notices of the Royal Astronomical Society, available online now. Videos depicting the swirling clouds are posted to YouTube.

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.

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 his 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.

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.

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.

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.


Science contacts

Alex Markowitz, in Germany
This email address is being protected from spambots. You need JavaScript enabled to view it. (preferred)
Tel: +49 (0)951 95222 26
Available for interviews in English only

Mirko Krumpe, in California, U.S.
Tel: +1 858 822 3435
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Available for interviews in German (preferred) or English

Robert Nikutta, in Chile
Tel: +56 9 7370 1865
Available for interviews in German or English



YouTube animations of clouds in orbit around a black hole are available from (with weather symbols) (with a diagram showing changing X-ray emission)

A NASA video with accompanying soundtrack is available from


Further information

The researchers publish their work in “First X-ray-based statistical tests for clumpy-torus models: eclipse events from 230 years of monitoring of Seyfert AGN”, A. G. Markowitz, M. Krumpe and R. Nikutta, Monthly Notices of the Royal Astronomical Society, in press.


Notes for editors

The Royal Astronomical Society (RAS,, founded in 1820, encourages and promotes the study of astronomy, solar-system science, geophysics and closely related branches of science. The RAS organizes scientific meetings, publishes international research and review journals, recognizes outstanding achievements by the award of medals and prizes, maintains an extensive library, supports education through grants and outreach activities and represents UK astronomy nationally and internationally. Its more than 3800 members (Fellows), a third based overseas, include scientific researchers in universities, observatories and laboratories as well as historians of astronomy and others.

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