Endeavour astronauts focus Hopkins telescope on brightening galaxy


Astronauts aboard the shuttle Endeavour are keeping a telescopic eye on a galaxy 54 million light-years from Earth that appears five times brighter than it did the last time NASA's Astro observatory looked at it, in 1990.

Called NGC 4151, the Seyfert-type galaxy has varied in brightness on a scale of days, said Baltimore's Arthur Davidsen, principal investigator on the Hopkins Ultraviolet Telescope (HUT), one of three telescopes orbiting on Endeavour with the Astro 2 mission.

HUT is being aimed at the galaxy's powerful core every two days in an effort to measure the day-to-day variability. The brightness has been seen to increase 10 percent in the first two days of observations.

HUT's ability to analyze the galaxy's light in wavelengths inaccessible to other telescopes is likely to provide new information about the galaxy's center.

"If it varies in a day, it can't be bigger than a light-day in size, and on a galactic scale, that's pretty small," he said.

It means that the galaxy's greatest energy is probably coming from hot gases as they swirl into a black hole with a mass equal to millions of suns.

(A light-day is the distance light travels in a day, or more than 16

billion miles. That's 174 times the distance from the sun to the Earth.)

NGC 4151 is one of two bright Seyfert galaxies targeted for observations yesterday by scientists as they moved into the sixth day of Astro's 15 1/2 -day mission. They already have gathered more data than they did during the troubled 1990 flight.

"It feels like we are drinking from a fire hydrant," said Dr. Davidsen.

Johns Hopkins astrogeophysicist Sam Durrance of Lutherville is one of two astronomers on the seven-member Endeavour crew, and a co-investigator on the HUT project.

"Sam appears to be in great spirits," said Bill Blair, deputy project scientist for HUT. "And from everything we can see, he is having a ball. He's setting [the telescopes] up on things quickly and sitting still on them."

The nine-day Astro 1 mission was dogged by problems with the telescopes' control systems. Half the planned observations were canceled.

"I'm so glad I hung around for Astro 2," Dr. Blair said.

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