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Zoom into the cloudy heart of an active galaxy. This animation shows an artist's rendition of the cloudy structure revealed by a study of data from NASA's Rossi X-Ray Timing Explorer satellite. Credit: NASA's Goddard Space Flight Center/Wolfgang Steffen, UNAMWatch this video on the NASAgovVideo YouTube channel.For complete transcript, click here. This animation shows an artist's rendition of the cloudy structure revealed by a study of data from NASA's Rossi X-Ray Timing Explorer satellite.Credit: Wolfgang Steffen, UNAM This animation uses familiar weather symbols — sunny, partly cloudy, and mostly cloudy — to illustrate how our viewing angle alters the apparent total cloud cover of a supermassive black hole. Credit: Wolfgang Steffen, UNAM Because the clouds absorb low-energy X-rays more strongly than high-energy X-rays, astronomers can measure the total density of gas along the line of sight directly from RXTE spectra. This animation shows changes in X-ray spectra corresponding to the number of clouds present at any instant along our line of sight.Credit: Wolfgang Steffen, UNAM At the hearts of most big galaxies, including our own Milky Way, there lurks a supermassive black hole weighing millions to billions of times the sun's mass. As gas falls toward a supermassive black hole, it gathers into a so-called accretion disk and becomes compressed and heated, ultimately emitting X-rays. The centers of some galaxies produce unusually powerful emission that exceeds the sun's energy output by billions of times. These are active galactic nuclei, or AGN.Using data from NASA's Rossi X-ray Timing Explorer (RXTE) satellite, an international team has uncovered a dozen instances where X-ray signals from active galaxies dimmed as a result of a cloud of gas moving across our line of sight. The new study triples the number of cloud events previously identified in the 16-year archive.The study is the first statistical survey of the environments around supermassive black holes and is the longest-running AGN-monitoring study yet performed in X-rays. Scientists determined various properties of the occulting clouds, which vary in size and shape but average 4 billion miles (6.5 billion km) across – greater than Pluto's distance from the sun — and twice the mass of Earth. They orbit a few light-weeks to a few light-years from the black hole. For More InformationSee [http://www.nasa.gov/content/goddard/rxte-reveals-the-cloudy-cores-of-active-galaxies/](http://www.nasa.gov/content/goddard/rxte-reveals-the-cloudy-cores-of-active-galaxies/) Related pages