The Cosmic Light No One Can Explain

By LEON JAROFF

It isn't visible to the naked eye, and when viewed through a large telescope it looks very much like any of the ordinary cosmic bodies in its celestial neighborhood. But this pinpoint of light is anything but ordinary. Spotted more than three years ago, it seemed at first to be a garden-variety star--but it wasn't. It might have turned out to be an unremarkable galaxy or quasar--but it didn't. Frustrated in their attempts to learn its nature, and even its distance from Earth, astronomers have begun to refer to the mystery object as, well, the "mystery object."

Just what the enigmatic body is has been the subject of much buzz in the astronomical community--and deservedly so. Astronomer S. George Djorgovski and his team at the California Institute of Technology first spotted the object in color photographs taken for an ongoing digitized survey of the northern skies. In one of the images, they noticed what seemed to be an oddly colored star in the constellation Serpens (the snake).

Intrigued, the Caltech team turned a larger telescope on the object to analyze its light. They were confident that the resulting spectrum, not unlike the band of colors that appears when sunlight is passed through a prism, would tell them a lot. "Once you have a star's spectrum," says Djorgovski, "you can determine its temperature, its heavy elements and how fast it's moving with respect to Earth."

Ordinarily, astronomers can take the measure of a star within hours after obtaining its spectrum. But when the Caltech astronomers got their first look at this object's spectrum, displayed in the form of an EKG-like graph on a computer screen, they were shocked. "Our mouths fell open," says Djorgovski. "I suspect that what we said was not printable. But the gist of it was, 'What the heck is this?'"

What stunned the scientists was where the peaks and dips of the graph fell. A trained astronomer can read a star's spectrum the way a forensic scientist reads a fingerprint, spotting almost at a glance the presence of an element like magnesium or carbon. But on this spectrum, something was drastically amiss. "It looks like somebody crumpled the spectrum," says Djorgovski. "It's not that we see things that we know about but are in the wrong place. It's simply that we don't know what they are."

The spectrum has two large peaks that may or may not mark an ample presence of an as yet unidentified element, and many small dips that probably represent segments of the spectrum where light has been absorbed by other elements--perhaps those in the object's outer atmosphere or in gas clouds between the object and Earth. Bewildered, the Caltech team looked for other answers. Maybe the object was a supernova, an exploding star, which often projects what Djorgovski calls a "weird-looking" spectrum. But the team observed the target a number of times over several months and noted no change. That ruled out a supernova's light, which gradually fades after the initial explosion.

Some of the astronomers then suggested that the spectrum resembled those of a particular category of quasars--fantastically bright and distant objects powered by black holes. Only one or two of them, known as iron broad-absorption quasars, have spectrums that bear a passing resemblance to that of the Caltech object. Could it be that a plethora of iron ions in the mystery object is distorting its spectrum?

"My personal guess," says Djorgovski. "is that we're dealing with a very special, sub-sub-sub-category of quasar. There may be only one of them." Or, he muses, his team may be looking at a quasar through a "very special" line of sight, a line that passes through a strange cloud of gas that accounts for its curious absorptions. But, he stresses, "I wouldn't stake any money on either of these possibilities."

The Caltech team was reluctant to publish a report that would merely say, in Djorgovski's words, "Gee, look what we've found," without offering a viable explanation. So after three years of examining and re-examining the spectrum and vainly searching through scientific literature, the team at last decided to go semipublic.

At the meeting of the American Astronomical Society in Chicago this spring, they showed their prize spectrum to other scientists and asked for their opinion. No one had seen anything like it, and few would hazard a guess about what message it might convey. Stymied at every turn, Djorgovski is pinning his hopes on investigating the object's invisible infrared emissions, which have wavelengths slightly longer than the red light at one end of the visible spectrum. Within the next few weeks, astronomers at the Keck Observatory in Hawaii will train a telescope equipped with an experimental infrared spectrograph on the quarry. What it captures could be revealing. "Our hope," says Djorgovski, "is that by seeing the longer wavelengths on the spectrum, we might actually notice a pattern that is familiar."

That insight might merely confirm that the Caltech astronomers have found an oddball quasar. Or it could herald the discovery of an entirely new and remarkable celestial object.