Astronomers in Chile said Wednesday they had caught the first-ever glimpse of a "supermassive" black hole preparing to gorge itself on gas clouds about a billion light years from Earth.

Using the ALMA telescope in the Atacama desert, the international team spotted three clouds streaming towards a black hole at speeds of up to 800,000 miles (1.3 million kilometres per hour).

Composed mainly of carbon monoxide, the clouds were "only" 300 light years from the huge hole, "essentially teetering on the edge of being devoured, in astronomical terms," the European Southern Observatory said in a statement.

The microwave-spectrum observation provides the first direct evidence for the theory that black holes feed on clouds of gas.

"It was magical being able to see evidence of these clouds accreting onto the supermassive black hole," said Timothy Davis of Cardiff University, who took part in the research.

"This is telling us more about what they (supermassive black holes) like to eat and how they evolved," he told AFP by telephone.

The researchers cannot observe the black hole directly, inferring its presence from the motion of objects around it.

The observation was an accidental one, the teams were trying to measure how many stars are born in the galaxy when they spotted the clouds.

"We use the black hole as a backlight," said Davis. "So, the black hole itself obviously emits no radiation but as stuff falls into the black hole that stuff is heated to very high temperatures and that material emits a lot of light.

"So what we see in this case is the shadow of the clouds as they fall into what's the black hole... they're between us and the black hole so they blank out some of this light."

Black holes are very dense regions in spacetime with a gravitational force so strong that even light cannot escape it -- making them invisible. 

Source: AFP