Mystery of The Cosmic Monster

By MICHAEL D. LEMONICK

Astronomers and physicists have learned repeatedly that the universe is more creative than they are. Time and again they have peered closely at the cosmos and discovered some object or phenomenon that they had never imagined could exist. The latest surprise came last week, and it forced scientists to drop whatever they were doing and scribble hurried calculations, even on napkins and scraps of envelopes. A report in the Astrophysical Journal claimed that something gigantic is hiding in the core of a distant galaxy called NGC 6240. Perhaps it is a black hole, a concentration of matter so dense that not even light can escape its powerful gravity. If so, it is more massive by far than any black hole ever detected. Or it may be something so bizarre that it does not fit into existing theories.

The history of science is full of similar discoveries, some of which have revolutionized ideas about the universe and many of which turned out to be less than they had seemed. In the former category, for example, is the 1936 discovery of a new particle, the muon, an elementary particle similar to the electron but more massive. Existing theories had predicted no such thing, and its appearance greatly complicated high-energy physics. "Who ordered that?" grumbled theorist I.I. Rabi at the time. But the muon and its kin led eventually to a new understanding of the subatomic world.

And then there are the breakthroughs that become embarrassments. Cold fusion is probably in this category. So is the discovery, reported two years ago, that under certain conditions a gyroscope weighs less when spun upside down. If that were true, it would force scientists to rewrite the laws of gravity.

Now comes the mysterious phenomenon in NGC 6240. It was first spotted in 1986 by astronomers working with a University of Hawaii telescope, but they checked and rechecked their puzzling findings before finally publishing a report last week. At first blush, it looks temptingly revolutionary. The apparent object is invisible, detectable only by its gravitational pull on surrounding gases. Calculation pegs its mass at about 100 billion times the mass of the sun, or about as much as the entire Milky Way. Yet it is squeezed into a mere 3,000 light-years, only about one-thirtieth the diameter of the Milky Way. The mass could come from tightly packed stars, but then their light should be blazingly bright, contend the report's authors. The only other choices: a black hole of unprecedented proportions, or some even more peculiar form of matter.

NGC 6240 is an abnormal galaxy though. In fact, it is really two galaxies in the process of colliding. The violence of the collision may account for the unexpected forces at work, rather than a black hole or some other strange object. And even if there is a great mass in the galaxy, it could be made of ordinary stars. All it would take to hide these would be a veil of dust.

At an informal lunch last week, members of Princeton's prestigious astrophysics department checked their envelopes and napkins and gave this discovery a preliminary thumbs-down. They think a simple explanation for the mystery of NGC 6240 will be found. All would admit, however, that they have been surprised before -- and will be again.