The most detailed observations ever of the dust around a huge black hole, at the centre of an active galaxy, have been gathered by European Southern Observatory’s Very Large Telescope Interferometer (VLTI).
Rather than finding all of the glowing dust in a doughnut-shaped torus around the black hole as expected, the astronomers found that much of it is located above and below the torus.
These observations show that dust is being pushed away from the black hole as a cool wind — a surprising finding that challenges current theories and reveals how supermassive black holes evolve and interact with their surroundings.
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Over the last twenty years, astronomers have found that almost all galaxies have a huge black hole at their centre.
Some of these black holes are growing by drawing in matter from their surroundings, creating the most energetic objects in the Universe: active galactic nuclei (AGN).
The central regions of these powerhouses are ringed by doughnuts of cosmic dust dragged from the surrounding space; similar to how water forms a small whirlpool around the plughole of a sink.
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It was thought that most of the strong infrared radiation coming from AGN originated in these doughnuts, but new observations of a nearby active galaxy called NGC 3783, harnessing the power of the VLTI at ESO’s Paranal Observatory in Chile, have surprised astronomers.
Although the hot dust — at some 700 to 1000 degrees Celsius — is indeed in a torus as expected, they found huge amounts of cooler dust above and below this main torus.
“This is the first time we’ve been able to combine detailed mid-infrared observations of the cool, room temperature dust around an AGN with similarly detailed observations of the very hot dust,” said Sebastian Honig from the University of California Santa Barbara, US and Christian-Albrechts-Universitat zu Kiel, Germany.
“This also represents the largest set of infrared interferometry for an AGN published yet,” said Mr. Honig, also lead author of the paper in The Astrophysical Journal .
The newly-discovered dust forms a cool wind streaming outwards from the black hole. This wind must play an important role in the complex relationship between the black hole and its environment.
The black hole feeds its insatiable appetite from the surrounding material, but the intense radiation this produces also seems to be blowing the material away.
It is still unclear how these two processes work together and allow supermassive black holes to grow and evolve within galaxies.
These new observations may lead to a paradigm shift in the understanding of AGN. They are direct evidence that dust is being pushed out by the intense radiation, the study said.