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. (*)
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