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January 20, 2002

More Up There Than Meets the Eye


Agence France-Presse
Satellites and electronic sensors have allowed scientists to peer beyond the narrow spectrum of visible light.

EVERY January, as though cheered by the completion of the Earth's latest jaunt around the sun, the field of astronomy explodes like a supernova spewing barrages of celestial news. The year 2002 has been no different, with arresting tales of effervescing "bubbles" light-years across — a kind of cosmic burp — and a towering fountain of gas erupting from a galaxy like a slow-motion volcano. The assortment of new planets has expanded once again, including a stillborn star called a brown dwarf orbiting its own sun.

The timing of the announcements is actually coincidental. January is when the American Astronomical Society holds the first of its two yearly meetings — the most recent was earlier this month in Washington — giving members a chance to reveal what they have been working on. Another burst of revelations comes every June at the summer meeting, the two events circling each other as rhythmically as binary stars.

For astronomy fans, the excitement eclipses the Super Bowl, with one report after another conjuring up visions of vast luminescent turmoil. But don't try to look too closely. To take in the whole show one would need not only a powerful telescope but eyes sensitive to a spectrum far wider than the narrow little rainbow people call visible light.

Every year, as satellites and electronic sensors further extend the visual range, more and more of the astronomical drama takes place on invisible stages. The familiar image of a laboratory prism casting its gradations of red, orange, yellow, green, blue, indigo and violet is so deeply ingrained that we forget that color — or, more precisely, electromagnetic radiation — stretches way beyond both edges of the scale.

To directly experience the thrill of the galactic fountain, observed by Dr. Edward M. Murphy, an astronomer at the University of Virginia, one would have to see far beyond blue with eyes that registered ultraviolet. Spewing from supernovae — exploding stars — these geysers of extremely hot gas vault into the galactic sky like Old Faithful before cooling and falling back down. Dr. Murphy was able to register the event, in the nearby Whale Galaxy (NGC 4631), using the Far Ultraviolet Spectroscopic Explorer, a satellite launched in June 1999 to study this small window of light.

Ultraviolet, with a frequency slightly higher than visible light, lies just beyond the eye's grasp. To see the gargantuan bubbles reported by Dr. Brian McNamara of Ohio University in Athens, one would literally have to have X-ray vision — the ability to register extremely high-pitched electromagnetic waves. Instead Dr. McNamara relied on the orbiting Chandra X-ray Observatory. What he found was evidence, in a cluster of galaxies called Abell 2597, of huge voids, or "ghost cavities," foaming through the surrounding gas — the aftershocks of ancient explosions ignited perhaps by matter falling into a black hole.

With its penetrating sensors, Chandra can also see through the stellar muck to the center of the Milky Way, revealing the black holes, neutron stars and other astronomical exotica lurking at its core. At the meeting, Dr. Q. Daniel Wang of the University of Massachusetts showed off stunning images — a pyrotechnical wonder of reds, greens, yellows and blues. (To make them pretty, his team took a bit of artistic license, substituting the familiar colors for various frequencies of X-rays.)

OTHER sessions of the meeting focused on sightings made with gamma-rays, the highest treble notes on the scale. Others concentrated on the bass notes at the opposite end: low- frequency radio and infrared emissions that provide their own points of view.

These days astronomers often find themselves pondering ways to map the universe without using light at all. Future Januarys may be filled with results from projects like LIGO (Laser Interferometer Gravitational- Wave Observatory), which aim to measure the faint waves of gravity emitted by collapsing stars, colliding black holes and other calamities. To make the delicate measurements, laser beams will be sent ricocheting between mirrors 2 1/2 miles apart, a distance that should subtly fluctuate as the Earth is buffeted by claps of gravity. By precisely measuring changes in the length of the beams, astronomers hope to listen in on the rumbling.

ACTUALLY, much of what scientists are learning about the universe already comes from studying gravity. The new planets often reported in January and June cannot actually be seen, even by the orbiting Hubble Space Telescope. Their existence is inferred from the way they cause their mother stars to wobble.

Thus one of the most satisfying finds revealed this month was a distant planet that could actually be observed by its light — and even the visible kind. Sixty-five times as massive as Jupiter, the orbiting body technically qualifies as a brown dwarf — bigger than a planet but not quite heavy enough to collapse in on itself, igniting the nuclear furnace that powers stars. Dr. Michael Liu of the University of Hawaii found the system, 58 light-years from Earth, using the Gemini North and Keck optical telescopes on Mauna Kea. They were rigged with computerized "adaptive optics": by compensating for atmospheric turbulence, they allow for sharper images of distant objects.

In the end there is still nothing more pleasing than good old-fashioned light. In fact, two Johns Hopkins University astronomers, Dr. Ivan Baldry and Dr. Karl Glazebrook, stole the show by demonstrating that the universe is pale green, somewhere between aquamarine and turquoise. This is a little strange considering that there are no green stars. Old ones are reddish and new ones are bluish. But when the light of all the stars is mixed together, the result is predominantly green.

It's a pleasing thought. If one could step outside the universe and view it from afar it would glow like a swimming pool at night. Now if only it were possible to see all those other colors.

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