Hopkins astronomer gets his quasar Shuttle telescope sees a billion light years away

December 06, 1990|By Frank D. Roylance | Frank D. Roylance,Evening Sun Staff

It was a sort of homecoming for Johns Hopkins University astronomer Arthur F. Davidsen. Only in this case, "home" was TC billion light years away.

At 6:40 p.m. yesterday, after suffering through more technical difficulties, astronauts aboard the space shuttle Columbia turned the Hopkins Ultraviolet Telescope (HUT) toward a brilliant object in the constellation Virgo known only as 3C273.

The object, the brightest quasar in the sky, is more than a billion light years beyond the outer edge of our Milky Way galaxy. But it shines with the luminosity of 100 million suns.

Scientists suspect the quasar is fueled by a super-massive black hole at the center of a large galaxy, an object with gravity so strong that nothing can escape its pull, even light. They think the quasar's enormous energy is generated by the destruction of stars as they are swept into the black hole like soap into a tub drain.

Seventeen years ago, Davidsen sent a small ultraviolet telescope to the edge of space aboard a sub-orbital rocket to look for 3C273, and he became the first astronomer on the planet to observe a quasar in the ultraviolet.

He managed to observe the quasar for only 250 seconds before the rocket fell back to Earth.

But the feat won Davidsen the Helen B. Warner Prize in 1979, astronomy's equivalent of the Nobel Prize.

Davidsen had worked for 13 years to develop, build and launch the Hopkins Ultraviolet Telescope to get another, much longer look at 3C273. Yesterday in Huntsville, Ala., he fulfilled his dream, when fellow astronomer Samuel T. Durrance aboard the shuttle focused HUT's ultraviolet detectors on the mysterious quasar for 30 minutes.

"It was a very emotional afternoon," said Lisa Hooker, a spokeswoman for the HUT team, which is gathered at the Marshall Space Flight Center in Huntsville.

It was a remarkable and important accomplishment for several reasons. First, ultraviolet light is ideal for studying the structure and behavior of very hot, very violent objects like quasars.

But because the Earth's atmosphere absorbs ultraviolet light, it can't be observed from the ground. Until space telescopes like HUT and Hubble, most ultraviolet astronomy had to be done with sounding rockets, which offer only brief exposures at best.

Second, because interstellar gases also absorb ultraviolet light, and since most quasars are so far away, the ultraviolet portion of their light is soaked up long before it can reach Earth.

But 3C273 is so close, at "only" one billion light years, that much of its ultraviolet light does reach Earth.

So, Davidsen's observations with HUT promise to provide astronomers with a great deal more information about the nature and origins of quasars and the universe itself than they've ever had to work with before.

The data they'll study will be spectrographic data, not photographs.

HUT does not take "pictures" as it orbits 220 miles above the Earth. It is a spectrographic telescope, which splits starlight into its component wavelengths. From its data, displayed on computer screens as graphs and charts, astronomers can learn a great deal about an object's chemical composition, temperature, pressure, speed and direction.

Hooker said Davidsen was "pleased with the spectrum . . . he was smiling." But it will be months before the data can be fully analyzed. HUT also is expected to return to 3C273 for another hour of observation before Columbia returns to Earth next Tuesday.

The HUT team had spent a nervous afternoon waiting for their chance at 3C273.

Earlier, the Astro telescopes had shut down, shifting into a "safe mode" after the shuttle briefly developed problems with a thruster. Later, there were more problems with the observatory's troublesome Instrument Pointing System.

In the end, Hooker said, Davidsen's long-time colleague Durrance actually steered the quasar into HUT's field of view.

When it was over, Davidsen asked shuttle controllers, "Would you please send my congratulations to Sam for getting the spectrum of 3C273?"

Davidsen "was pleased to have the observation safe in his hands," Hooker said.

Because of problems with the pointing system, the crew's astronomers have missed roughly half the celestial targets they had hoped to observe by now.

During intermittent failures of the automatic system, the astronauts wiggled a joystick and used a computer keyboard to position the telescopes manually, and got more proficient at aiming the observatory, NASA said.

NASA said the crew had charted just 45 of 86 intended targets through early yesterday. Updated figures were not immediately available, but officials were optimistic after yesterday's showing, mission spokesman Al Jordan said.

"We expect to show an improvement," he said.

Scientists had planned to begin using the observatory late Sunday, the day the shuttle lifted off.

The schedule for the 10-day mission is tight, but NASA said the crew might be able to make up a few hours' viewing time toward the end of the flight if things go well.

Mission scientist Ted Gull could not say when the observatory might reach peak efficiency, but he was confident that fine-tuning would increase viewing time.

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