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Viewing the dust that fuels a distant black hole

May 16, 2012|By Thomas H. Maugh II
  • An artist's conception of the distant galaxy NGC 3783, which has a supermassive black hole at its center.
An artist's conception of the distant galaxy NGC 3783, which has a… (European Southern Observatory )

Using as many as three telescopes located on a mountaintop in Chile's barren Atacama Desert, astronomers from the European Southern Observatory have managed to image a small galaxy, only half a light-year across, at a distance of 130 million light-years from Earth. Viewing it with a single telescope would have required one with a mirror diameter of 130 meters (426.6 feet), more than 48 times bigger than the mirror at the iconic Mt. Palomar telescope in Southern California.

Astronomers at the Max Planck Institute for Radio Astronomy in Bonn, Germany, obtained the image by using interferometry, a technique in which light from two to three telescopes is combined to produce high-resolution images. The image obtained is equivalent to that which would be yielded by a telescope with a mirror the size of the distance between the two telescopes. In this case, that distance was 130 meters.

Most galaxies have a black hole at their center, and many have so-called supermassive black holes, with masses more than a million times greater than that of our sun. The black holes themselves cannot be imaged directly because their gravitation is so strong that they allow no radiation to escape. But they are surrounded by a hot, bright gas disk called the accretion disk, which is illuminated by the energy released when gas molecules plunge into the black hole. That, in turn, is surrounded by a dust torus, a doughnut-shaped blob of cooler gas that provides new fuel for the accretion disk. Without this supply of new fuel, the accretion disk would eventually grow dim and disappear. The dust torus of NGC 3783, imaged by a team headed by astronomer Gerd Weigelt of the Max Planck Institute, has an angular radius in the Earth's sky of only 0.7 milliarcseconds, less than one five-millionth of one degree.

The research team recorded thousands of images of the galaxy. Those images, Weigelt said, will help astronomers better understand the violent processes that occur at galactic centers. Further research will examine the same galaxy at shorter wavelengths of light and with longer baselines between telescopes, which will improve resolution even further.

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