NASA's SOFIA detects cool dust around active black holes!

New Delhi: Black holes and their behaviour have been long since been no less than an enigma for scientists to decipher.

Found in abundance in the universe, these gravity-pulling, star-devouring black holes have always been known to exist in distant galaxies.

A supermassive black hole, however, is the largest type of black hole, on the order of hundreds of thousands to billions of solar masses, and is found in the centre of almost all currently known massive galaxies.

In this regard, the observations of the Stratospheric Observatory for Infrared Astronomy or SOFIA – a collaborative initiative of NASA and the German Aerospace Center (DLR) – have been assessed and examined to discover that 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 percent 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 percent 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.

(With IANS inputs)