Simulation of AGN clouds seen by RXTE
Credit: NASA's Goddard Space Flight Center/Wolfgang Steffen, UNAM

Clouds from Both Sides Now

Supermassive black holes are what put the activity in active galaxies. At the centers of active galaxies, a hungry black hole millions or billions of times more massive than the Sun generates more energy than the entire rest of the galaxy. It does this by swallowing enormous amounts of matter from its surroundings. All this power is generated in an incredibly small space: a billion solar mass black hole, placed at the center of our solar system, would comfortably fit within the orbit of Neptune. Central black holes in active galaxies are surrounded by a thick disk of material orbiting far beyond the black hole's reach, and our line of sight towards the black hole, either through this torus or perpendicular to it, accounts for the variety of active galaxies out there - blazars show bright central cores, while radio galaxies show centers that are relatively faint, but with huge radio and X-ray emitting jets extending from the galaxy for hundreds of lightyears or more. The relation between the outer torus and the inner accretion disk which feeds the black hole is a bit of a puzzle to astronomers. Using 16 years of data from NASA's Rossi X-ray Timing Explorer (RXTE) archive, astronomers have now provided the best study of the structure of the tori around a selection of the 153 active galaxies that RXTE observed during its mission (it was decommissioned by NASA in 2012). These astronomers were able to identify 12 eclipses of supermassive black holes in 8 galaxies by thick clouds in the obscuring torus. This nearly triples the previous number of detected eclipse events. These eclipses reveal that at least some tori are composed of discrete clouds that average 4 billion miles across with twice the mass of Earth, lying a few light-weeks to a few light-years from the black hole. The image above shows an artistic impression of a central supermassive black hole in an active galaxy with its cloudy torus, while an accompanying video shows how clouds in the dynamic torus eclipse the central black hole.
Published: April 7, 2014

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Page Author: Dr. Michael F. Corcoran
Last modified Monday, 14-Apr-2014 06:52:16 EDT