A U.S. space telescope, peering into a cloud of dust and gas, has spotted a hidden collection of supermassive black holes. A finding that suggests many more may exist in the universe if we know where to look.

A team of international researchers used NASA's Nuclear Spectroscopic Telescope Array satellite observatory to detect the high-energy emission of X-rays from the giant black holes, previously hidden from direct observation within the shroud of dust and gas.

Most galaxies are assumed to have such giant cosmic beasts at their centers actively devouring material, but observing them is often a challenge through intervening dust and gas clouds.

To track them down, the scientists turned NuSTAR toward nine separate galaxies where they thought giant black holes might be highly active but for the most part obscured.

Five galaxies did in fact reveal hidden supermassive black holes to NuSTAR and they were even more extremely active than was previously assumed.

Led by astronomers at Durham University in the United Kingdom, the new research strongly supports theories that the universe could contain millions of such supermassive black holes, with many of them, or perhaps even a majority, hidden from view.

"Thanks to NuSTAR, for the first time, we have been able to clearly identify these hidden monsters that are predicted to be there, but have previously been elusive because of their surrounding cocoons of material," says Durham astronomer George Lansbury, first author of a study to be published in the The Astrophysical Journal.

"Although we have only detected five of these hidden supermassive black holes, when we extrapolate our results across the whole universe, then the predicted numbers are huge and in agreement with what we would expect to see," he says.

Such detections were impossible before the 2012 launch of NuSTAR, which can detect X-rays at much higher energy levels than was possible with previous space-based observatories.

"High-energy X-rays are more penetrating than low-energy X-rays, so we can see deeper into the gas burying the black holes," explains NuSTAR project scientist Daniel Stern at NASA's Jet Propulsion Laboratory in Pasadena, California.

"NuSTAR allows us to see how big the hidden monsters are, and is helping us learn why only some black holes appear obscured," he says.