Active supermassive black holes are wrapped in cool dust, NASA's SOFIA Telescope discovers

NASA's Stratospheric Observatory for Infrared Astronomy, SOFIA, has detected cool dust around the black holes that are energetic active. The researchers at the University of Texas San Antonio have observed that the dust surrounding these black holes is much more compact than previously thought.

Most of the massive galaxies are home to a supermassive black hole which exists at the centre. Many of these black holes are relatively inactive and quiet. One of the examples is the black hole which is present at the centre of our Milky Way galaxy.

However, there are some supermassive black holes that emit huge amounts of energy because they consume significant amounts of material that are being drawn into them. Such active black holes are known as active galactic nuclei.

As per previous studies, all the active black holes or active galactic nuclei have a donut-shaped structure called a torus and surrounds the supermassive black hole.

The team used the instrument called the Faint Object infraRed CAmera for the SOFIA Telescope, FORCAST to study the infrared emissions found around 11 supermassive black holes in active galactic nuclei located at distances of 100 million light years and more. They also determined the size, opacity and distribution of dust in each torus.

The study has been published in the Monthly Notices of the Royal Astronomical Society. The team has said in the report that the tori are 30 per cent smaller than predicted. It has also said that the peak infrared emission is at even longer infrared wavelengths than previously thought. 

The implication is that the dust obscuring the central black hole is more compact that previously thought.

Also, there are indications that most of the energy radiated by active galactic nuclei is at wavelengths that are not observable from the ground as the water vapour in Earth’s atmosphere absorbs the energy.

Flying above 99 per cent of the Earth’s water vapour, SOFIA allows the team to characterize the properties of the torus-shaped dust structures at far-infrared wavelengths.

"Using SOFIA, we were able to obtain the most spatially detailed observations possible at these wavelengths, allowing us to make new discoveries on the characterization of active galactic nuclei dust tori," said Lindsay Fuller, graduate student at the University of Texas San Antonio and lead author of the published paper.

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Future observations are necessary to determine whether or not all of the observed emission originates with the tori, or if there is some other component adding to the total emission of the active galactic nuclei. 

"Next, our goal will be to use SOFIA to observe a larger sample of active galactic nuclei, and at longer wavelengths. That will allow us to put tighter constraints on the physical structure of the dusty environment surrounding the active galactic nuclei," Enrique Lopez-Rodriguez, principal investigator of this project and Universities Space Research Association staff scientist at the SOFIA Science Center said.

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