In the heart of MCG-6-30-15, a galaxy 130 million light-years away, there is a hole. It’s as big around as the orbit of Mars. Into this hole stars and star stuff are always falling—a lot of stuff, the equivalent of a hundred million suns so far. From this hole nothing escapes, not even light. It is perfectly black, like the mouth of a long tunnel. If you were to get into a spaceship and put it into orbit around this perfect blackness, you would find, once you got close enough, and even before you started your final descent into darkness, that you were no longer in control. You would be swept along by an irresistible current, not of swirling gas or stardust but of space-time itself.
That’s because the black hole in MCG-6-30-15 is spinning. And as it spins, it drags space-time around with it.
No spaceship has been there to check it out, of course. And none of this is directly visible from Earth. From our planet, MCG-6-30-15 doesn’t look like much. It’s a lenticular galaxy, a lens-shaped blob of stars without the photogenic spiral arms that mark our Milky Way galaxy. “It’s very undistinguished,” says Cambridge University astronomer Andrew Fabian, who has been studying it for more than a decade. “If you were to use an optical telescope and just look at images, you wouldn’t jump up and down.” But if you look at the galaxy with a different kind of telescope, it comes alive. As gas falls toward the central black hole, before it disappears from the universe forever, it becomes so hot that it emits X-rays, which astronomers can collect and plot on a spectrum.
In 2002 a team led by Jörn Wilms of the University of Tübingen in Germany published the best spectrum yet for MCG-6-30-15. That doesn’t look like much either, just a gently sloping line of data points, with a small spike at the top. But it was Figure 1 in the researchers’ paper [pdf]—there was no Figure 2—and although they did not actually jump up and down when they first saw it, they did get quite excited. “We just didn’t believe what it was,” Wilms says. That graph, he and his colleagues claim, says it all if you read it right. It represents a giant black hole spinning at nearly the speed of light, the space-time around it twisted like a whirlpool, and the fluorescent iron atoms that trace that fantastic motion cast like leaves on swirling water.
All that—and one more thing. The X-ray glow of those iron atoms is so intense that gravitational heating alone cannot explain it. What that unassuming little graph may represent is the detection of a new source of cosmic energy, one predicted a quarter century ago but never before observed. Some theorists believe a large fraction of all the light in the universe, including its most spectacular displays—the jets of radiant gas that shoot out of certain galaxies at near- light speed—may be generated this way. Its basic principle is familiar; Michael Faraday discovered it in 1831. But the setting is exotic, to say the least. If Wilms and his colleagues are right, there is not just a hole but also an electromagnetic generator at the heart of MCG-6-30-15, one that takes the rotational energy of swirling space-time and converts it into light, much as an alternator spinning atop an auto engine spits out electricity.
