Astronomers see huge clouds of gas orbiting supermassive black holes at the centers 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, they report in a paper to be published in the Monthly Notices of the Royal Astronomical Society, available online now.
The clouds they observed orbit a few light-weeks to a few light-years from the centers of active galactic nuclei. One in a spiral galaxy in the direction of the constellation Centaurus, appeared to be in the midst of being torn apart by tidal forces. Video produced by the Scientific Visualization Studio, Goddard Spaceflight Center, NASA, based in part on visualizations created by Wolfgang Steffen, Institute of Astronomy, National Autonomous University of Mexico.
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 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.
Support for this research came from NASA's Astrophysics Data Analysis Program and the European Community's Seventh Framework Program. Nikutta acknowledges support from ALMA-CONICYT.