Revealing space’s secret supermassive black holes

Specialist technology 

Standard telescopes are unable to find these hidden supermassive black holes, which are veiled beneath thick blankets of dust and gas and can’t even be detected by low-energy X-ray light. 

Thanks to specialist technology, the team have revealed that the number of unseen or undiscovered black holes is over double the previously estimated number.

Using data taken from NASA’s InfraRed Astronomy Satellite and the X-ray space telescope NuSTAR, the astronomers have captured these black holes by viewing the infrared emissions from clouds surrounding supermassive black holes.

Poshak Gandhi, Professor of Astrophysics at Southampton, explains: “Though black holes themselves are dark, they can heat up surrounding gas which glows intensely, making them some of the brightest objects in the universe. 

“Even when hidden, the surrounding dust absorbs and re-emits this light as infrared radiation, revealing their presence. At the same time, X-rays provide a complementary view peering through the veiling gas, much like a medical X-ray scan allows a doctor to peer through to our innards.”

Poshak reveals that this discovery will give us a clearer picture of just how many of these giants surround us in the universe.

Shaping galaxies

Comparing these hidden black holes to non-hidden ones can give scientists an insight into how these black holes grow and behave, and how they change galaxies. 

“If they do grow by consuming material, then a significant number should be surrounded by thick clouds and potentially obscured,” says lead author Dr Peter Boorman, formerly of the University of Southampton and now at the California Institute of Technology (Caltech).

The census found that about 70% of growing supermassive black holes are hidden in this way, with the most deeply embedded population accounting for 35%. Growing black holes are very shy and hard to detect.

“Black holes influence the galaxies they live in – this happens because they are surrounded by massive clouds of gas and dust and can consume vast amounts of material,” Peter adds.

“If too much falls toward a black hole, it starts coughing up the excess and firing it back out into the galaxy. That can disperse gas clouds within the galaxy where stars are forming, slowing the rate of star formation.”

Revealing these hidden black holes, and exploring their behaviour, will give us a better insight into how they behave, and just how much the universe has been changed by their presence.