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Astronomy 100

 

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January 10, 2002

X-Rays Define Clear Images of Milky Way

By JOHN NOBLE WILFORD

WASHINGTON, Jan. 9 Peering deep into the heart of the Milky Way with X-ray vision, an American spacecraft has produced what astronomers say is the sharpest-ever image of the most dynamic region of Earth's home galaxy.

A team of astronomers led by Dr. Q. Daniel Wang of the University of Massachusetts at Amherst reported here today that NASA's Earth-orbiting Chandra X-ray Observatory had detected more than 1,000 discrete sources of the powerful X-rays, far more than the dozen sources previously known.

"This is an important step toward understanding the most active region of our galaxy," Dr. Wang said at a meeting of the American Astronomical Society. "It gives us a new perspective of the interplay of stars, gas, dust and gravity at the very epicenter of the galaxy."

Until the advent of X-ray spacecraft, especially Chandra, a detailed examination of the Milky Way's core had been impossible, since most of it is obscured in a smog of gas and dust. By penetrating this smog, scientists said, the new research could lead to insights into what is happening at the centers of other galaxies.

The Chandra images cover a region 400 light years wide by 900 light years long, in the galactic suburbs some 20,000 light years away from the Sun. Looking at the glittering arc of the Milky Way in the summer from the Northern Hemisphere, its center would be close to the southern horizon. The best view at all times is from the Southern Hemisphere.


But the X-ray images reveal phenomena unseen in other wavelengths, even by the most powerful ground-based telescopes.

In their analysis, Dr. Wang and his colleagues Dr. Cornelia Lang, also of the University of Massachusetts, and Dr. Eric Gotthelf of Columbia University determined that most of the discrete X-ray sources were from remnants of dead stars, like white dwarfs, neutron stars and black holes.

The more diffuse X-ray emissions in the region, the astronomers said, had lower energies and seemed to come from gases not as hot as once thought, a relatively mild 10 million degrees. Their source appeared to be the titanic turbulence all around.

Stars are forming there at a much more rapid rate than elsewhere in the galaxy. And stars are exploding more frequently than elsewhere, the supernovas emitting tremendous shock waves and a blizzard of debris.

"It's a great image," said Dr. Farhad Yusef-Zadeh, an astronomer at Northwestern University.

But noting that other scientists suspected that the collisions of low- energy cosmic rays could also be responsible for the radiations, Dr. Yusef-Zadeh added that "the origin of the hot gas remained a mystery."

For another view of the Milky Way, Dr. Michael Skrutskie of the University of Virginia reported using infrared data from 30,000 stars to trace the outlines of the galaxy's complete disk. He called it the first- ever bird's-eye view of the galaxy.


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Daniel Wang Astronomy 100