Using observations from NASA’s Stratospheric Observatory for Infrared Astronomy, SOFIA, researchers have found that the dust surrounding active, ravenous black holes is much more compact than previously thought. Most, if not all, large galaxies contain a supermassive black hole at their centres. Many of these black holes are relatively quiet and inactive, like the one at the centre of our Milky Way galaxy. However, some supermassive black holes are currently consuming significant amounts of material that are being drawn into them, resulting in the emission of huge amounts of energy. These active black holes are called active galactic nuclei.

SOFIA flies above 99 per cent of the Earth’s water vapour, enabling the research group to characterise 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 characterisation of active galactic nuclei dust tori,” said Lindsay Fuller, graduate student at the University of Texas San Antonio and lead author of the study.

Previous studies have suggested that all active galactic nuclei have essentially the same structure. Models indicate that active galactic nuclei have a donut-shaped dust structure, known as a torus, surrounding the supermassive black hole. The team observed the infrared emissions around 11 supermassive black holes in active galactic nuclei located at distances of 100 million light years and more, and determined the size, opacity, and distribution of dust in each torus.

In a paper published in the Monthly Notices of the Royal Astronomical Society, the team said that the tori are 30 per cent smaller than predicted and that the peak infrared emission is at even longer infrared wavelengths than previously estimated. The implication is that the dust obscuring the central black hole is more compact that previously thought.