Hanny's Voorwerp
Credit: WIYN/William Keel/Anna Manning

Unseen is Important

Often the story's told by what's there, though sometimes what's missing is most important. This has turned out to be the case in the explanation of Hanny's Voorwerp, a mysterious green glow found by Hanny van Arkel, a Dutch school teacher and avid participant in the Galaxy Zoo project. Galaxy Zoo lets volunteers scan online images of galaxies to categorize them and to search for peculiar and mysterious cosmic objects. Such as the Voorwerp (Dutch for "object") shown in the image above, just below the large spiral galaxy IC 2497. The Voorwerp is really a huge patch of ionized gas and an intense puzzle to astronomers. Illumination by radiation produced by a supermassive blackhole in the center of IC 2497 was presumed a likely culprit, but optical images of IC 2497 showed no sign of the tell-tale activity expected near the nucleus of the galaxy. Maybe the active supermassive black hole is really hidden by thick clouds of gas and dust in the galaxy's nucleus. Astronomers tried to detect infrared radiation from these clouds, to no avail. Then, using the Suzaku X-ray satellite, astronomers tried to directly detect evidence of a hidden active black hole in IC 2497 using the penetrating power of its hard X-ray emission. But Suzaku showed no signs of any such X-ray emission. Strangely, this means that the black hole near the center of IC 2497 shut off in the recent past, and the Voorwerp is only a faint echo of this once-mighty beast. A case of sudden death on a cosmic scale.
Published: December 13, 2010

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Page Author: Dr. Michael F. Corcoran
Last modified Saturday, 15-Jul-2017 12:30:31 EDT