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Science - Associated Press - updated 10:41 AM ET Sep 5
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Wednesday September 5 10:40 AM ET

Milky Way May Have Black Hole

By JOHN BIEMER, Associated Press Writer

A powerful new X-ray telescope has yielded evidence that virtually clinches the case for the existence of a supermassive black hole at the center of our galaxy, astronomers say.

Scientists generally hold that almost every galaxy revolves around a black hole. Previous studies have estimated that the center of our galaxy, the Milky Way, contains something very dense and massive, which most scientists already believed was a black hole.

Black holes are extremely dense celestial objects. Their gravity is so powerful that not even light can escape them, making them invisible to conventional telescopes.

To study them, astronomers observe stars and gas swirling around the center of a black hole before they fall into its invisible core like water swirling down a drain. Before going in, matter stacks up as if in a logjam, where it heats up and generates X-rays.

In the new study, led by Frederick Baganoff of the Massachusetts Institute of Technology (news - web sites), scientists used NASA (news - web sites)'s $1.5 billion Chandra X-ray telescope to observe a flare of X-ray energy produced where the lip of the black hole should be. The clear-cut image of the flare was the first of its kind.

The flare dimmed and brightened over 10 minutes, the time it would take for light to travel about 93 million miles around the lip of a black hole.

That means the object that is believed to be a black hole is fairly small in space terms. The mass stuffed within that area is about 2.6 million times that of the sun.

``We are now able to say that indeed all of the mass, by implication, is within that small region, and there is nothing we know that can be that dense and not be a black hole,'' Baganoff said.

The apparent black hole is 24,000 light-years from Earth.

Richard Mushotzky, an astronomer with NASA's Goddard Spaceflight Center in Greenbelt, Md., said the new findings push previous evidence of a black hole in the center of the Milky Way ``one step further.''

``It's gone from a reasonable supposition to very hard to believe it's not true,'' he said.

The study appears in Thursday's issue of the journal Nature.

The observations would not have been possible without the Chandra observatory, NASA's most powerful X-ray telescope. Launched into orbit two years ago, it uses four cylindrical nesting mirrors to funnel incoming X-rays.

Such X-rays are absorbed by the atmosphere and cannot be detected well by ground-based telescopes.

Scientists believe there are billions of black holes in the universe, including many that are thousands of times more massive and vastly more luminous than the object at the center of the Milky Way.

Because scientists did not have an image of an X-ray flare before, some suggested that the dense object in the center of our galaxy was a clump of dark stars rather than a black hole.

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