Astronomers glimpse energy exiting a black hole

For the first time, astronomers may have spotted energy coming out of a black hole, a spherical chasm in space and time from which nothing was thought to be able to escape.

The supermassive black hole lies in the heart of a galaxy 120 million light years away, where it spins in the middle of a gigantic disk of hot matter and energy. This "accretion disc" drags on the black hole, causing it to slow and lose energy, say researchers working with the orbiting XMM-Newton X-ray observatory.

The lost energy heats the inner edge of the accretion disk so that it produces telltale X-rays, report Jцrn Wilms of University of Tьbingen, Germany, and colleagues in a forthcoming paper.

Black holes that consume accretion disks are thought to power astronomical phenomena ranging from quasars to gamma ray bursts, says Christopher Reynolds, a team member and astrophysicist at the University of Maryland in College Park. "This new powerful energy source might be relevant in a whole host of objects," he says.

Uncertain model

The result is exciting, but it depends on uncertain mathematical models of accretion disks, says Chris Done, an astrophysicist at the University of Durham in the UK. "I don't think they have shown that from the data their conclusions are absolutely necessary," she says.

The X-rays in question come from iron in the accretion disk. Usually such X-rays all have nearly the same energy, but the X-rays from the black hole have a broader range of energies. That implies they are coming from the very inner edge of the disk, where matter swirls at a range of speeds, causing the energies of the X-rays to spread.

However, the disc also produces other X-rays and the mathematical models are needed to account for this background.

Angels' wings

If the black hole is losing energy, it confirms a prediction made more than 25 years ago by astronomers Roger Blandford and Roman Znajek.

They suggested that an accretion disc could generate a magnetic field that would latch on to a spinning black hole as it twists space and time around it. This "friction" would slow the black hole down, heating the disc.

But the idea remains speculative because researchers still do not understand precisely how the disc produces a field, Done says: "When most astrophysicists start invoking magnetic fields, they might as well say 'when angels flap their wings'."

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