Space telescopes have combined to take a snapshot of the sky that reveals more than a thousand of the biggest black holes in the universe. The hungry monsters are each up to several billion times more massive than the sun and they lie in the centres of galaxies.

Light cannot escape from a black hole because its gravitational pull is so strong. However, they show themselves thanks to the huge amounts of light and energy generated by stars and dust as they fall into them.

Astronomers used an X-ray space telescope called Chandra plus Spitzer, a heat-seeking infrared observatory in orbit, together with data from telescopes on the ground to take their snapshot.

It covers an area of sky more than 40 times the apparent area of the full moon in the constellation of Bootes, the herdsman. The black holes show up as red, green or blue dots, depending on the level of X-rays they emit.

Ryan Hickox of the Harvard-Smithsonian Centre for Astrophysics in Cambridge, Massachusetts, said: “We’re trying to get a complete census across the universe of black holes and their habits.”

Instead of staring at one relatively small part of the sky for a long time, this team scanned a much bigger portion with shorter exposures. Co-investigator Christine Jones said: “With this approach, we found well over a thousand of these monsters, and have started using them to test our understanding of these powerful objects.”

The investigators say their new survey raises doubts about a popular current model of a supermassive black hole which says it is surrounded by a doughnut-shaped region, or torus, of gas.

Read the full release here. Picture: X-ray: NASA/CXC/CfA/R.Hickox et al.; Moon: NASA/JPL

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