June 20, 2013
Black Hole Observed Pushing Matter Away, Rather Than Consuming It
Lawrence LeBlond for redOrbit.com - Your Universe Online
Observations of a nearby active galaxy using the Very Large Telescope Interferometer (VLTI) at ESO´s Paranal Observatory in Chile have shown astronomers something they hadn´t expected to see.
Astronomers have found over the past twenty years that nearly all galaxies have a black hole at their center, some of which grow by drawing in matter from their surroundings. This growth process creates some of the most energetic objects known in the Universe: active galactic nuclei (AGN). The central regions of these often supermassive black holes are ringed by cosmic dust, and it was commonly believed that most of the infrared radiation coming from AGN originated in these doughnut-shaped rings.
However, the new observations in galaxy NGC 3783 were surprising. Although the hot dust “between 1300 and 1800 degrees Fahrenheit" was found to indeed be part of a doughnut-shaped ring, or torus, astronomers also found large amounts of cooler dust both above and below the main ring.
The observations show that dust is continuously being pushed away from the black hole as a cool wind. This surprising find challenges current theories as it gives astronomers a new look at how supermassive black holes evolve and interact with their surroundings.
"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. This also represents the largest set of infrared interferometry for an AGN published yet," explained lead author Sebastian Hönig from University of California-Santa Barbara and University of Kiel in Germany.
The cool dusty wind that streams outward from the black hole plays an important role in the complex relationship between the black hole and its environment, according to the researchers. They added that the black hole not only feeds itself on the surrounding material, but also blows material away due to the intense radiation produced by feeding. It is unclear as to how these processes work together and allow the supermassive black hole to grow and evolve within galaxies, but the researchers note that the presence of cool dusty wind adds new evidence to the mystery.
Astronomers knew in order to investigate the central regions of NGC 3783 in more detail, they needed to implement the combined power of the Unit Telescopes of ESO´s Very Large Telescope. By using the units together, the team was able to form an interferometer that can obtain a resolution equivalent to that of a 130-metre telescope.
"By combining the world-class sensitivity of the large mirrors of the VLT with interferometry we are able to collect enough light to observe faint objects. This lets us study a region as small as the distance from our Sun to its closest neighbouring star, in a galaxy tens of millions of light-years away. No other optical or infrared system in the world is currently capable of this," said Gerd Weigelt, a team member from Max-Planck-Institut für Radioastronomie, Bonn, Germany.
The team believes these new observations could lead to a paradigm shift in the understanding of AGN. The observations are direct evidence that dust is being pushed away by intense radiation. They add that new models must take into account the newly-discovered effects of how dust is distributed and how supermassive black holes grow and evolve.
"I am now really looking forward to MATISSE, which will allow us to combine all four VLT Unit Telescopes at once and observe simultaneously in the near- and mid-infrared – giving us much more detailed data," concludes Hönig.
MATISSE is a second-generation instrument currently being constructed for the VLTI.
The research paper, entitled "Dust in the Polar Region as a Major Contributor to the Infrared Emission of Active Galactic Nuclei," is published on June 20, 2013 in the Astrophysical Journal.