A Real Space Monster

By MICHAEL D. LEMONICK

To hear people talk, there are "black holes" all around us: the U.S. deficit, the Russian economy, the Chicago Post Office. They are found wherever things seem to disappear wholesale without leaving a trace. Ever since Princeton physicist John Wheeler coined the term in 1967 to describe an object whose gravity is so powerful that it swallows everything around it -- even light -- this bizarre concept, which first emerged from Einstein's equations of general relativity, has been part of everyday language.

While journalists and ordinary folks have been throwing the expression around loosely, astronomers have been searching for the real thing. The evidence so far has been tantalizing but circumstantial. Last week, however, nasa announced that the newly sharp-eyed Hubble Space Telescope has found something strange lurking about 50 million light-years away, at the core of galaxy M87 -- something with the mass of more than 2 billion stars the size of the sun crammed into a space no bigger than our solar system. The only thing scientists know of that could possibly fit this description: a gigantic black hole.

The astronomers didn't actually see the hole, of course, since it is invisible by definition. What they detected was a disk-shaped cloud of gas rotating at a dizzying 1.2 million miles an hour. A disk of gas is just what researchers expect to see around a black hole: any star that ventures too close will first be ripped apart by the hole's intense gravity and then start to spiral in, the way water spirals down a bathtub drain. As it is being sucked in, the gas should be compressed and heated -- and in fact the gas disk in M87 is glowing with a temperature of about 18,000 degrees F.

It was the speed, though, that convinced astronomers that they had nabbed their black hole at last. The rules of celestial mechanics dictate that the speed of an orbiting body must depend on the mass of whatever it is orbiting and the distance between the two. Given the incredible velocity and 60-light- year diameter of the gas cloud in question, it has to be circling something of unprecedented mass and density.

How did the black hole form in the first place? It could have started with a large star that burned out its nuclear fuel and then collapsed. If the star was big enough, the implosion would have been so violent that all the atoms would have been crushed out of existence. The entire star would have been squeezed into an immeasurably small size, and its density and gravity would have increased enormously. Over the universe's 15 billion-year history, billions of other stars could have ventured too close and been sucked in, making the hole grow ever more massive and powerful.

Though M87 is the first supermassive black hole ever discovered, astronomers are convinced that such objects lie at the heart of many galaxies. The powerful forces unleashed as the holes gobble up stars and gas may be the source of quasars, mysterious beacons of light so bright that they're visible across the universe. There are even hints of a giant black hole in our own Milky Way. But the sun is too far away to be in any danger of falling in. The only "black holes" we have to fear are the metaphorical ones here on Earth.