However, the furious activity that occurs around the rim of the black hole, before matter falls into it, appears to generate the magnetic fields, the Los Alamos scientists said at a meeting of the American Astronomical Society, in Albuquerque.

The energy contained in these huge magnetic fields is comparable to that released into space as light, X-rays and gamma rays, which means that the black hole's power generator is highly efficient, according to astronomer Philipp Kronberg.

There is an upper limit to how much energy each black hole can put out, Kronberg said at a news conference, and there is "an uncomfortably small gap between the size of the fuel reservoir and the actual energy that has to be put out.

"What this tells us is that the energy has to be put out very efficiently," Kronberg said.

He said systems like the one in the image may tend to spread out into intergalactic space. "And if they have, it means that there's a substantial fraction of energy in intergalactic space."

This energy might have been generated by a very dense, super-small but super-massive black hole, Kronberg said.

Black holes can theoretically be billions of times the Sun's mass, but scientists have also postulated that tiny ones also exist.