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Tuesday, September 8, 1998 Published at 10:33 GMT 11:33 UK


Massive black hole at galaxy's core

Swirling gas clouds at the galactic core

There is an enormous black hole at the centre of our galaxy according to astronomers. Our science editor Dr David Whitehouse reports.

Black holes are formed from the remnants of collapsed stars. A black hole consists of a large mass squashed so much that not even light can escape from its force of gravity.

For many years scientists have speculated that at the centre of our galaxy there may be a great concentration of matter in the form of a supermassive black hole. Now they have some evidence for it.

It has been found because of the black holes gravitational effect on nearby stars and gas clouds.

[ image: The Keck telescope: tracked 200 stars]
The Keck telescope: tracked 200 stars
Using the Keck telescope atop the Mauna Kea extinct volcano in Hawaii, astronomers have tracked the movements of 200 stars near the galactic centre.

Some of them displayed signs of influence by extreme gravitational forces.

These stars are spiralling around the black hole at speeds of up to three million miles per hour - about 10 times the speed at which stars typically move.

To account for these speeds it is estimated that an object 2.6 million times more massive than the sun must be concentrated into a single black hole.

The centre of our galaxy lies 30,000 light years away behind vast clouds of stars, gas and dust.

To peer through this obscuration the scientists used a technique called infrared speckle interferometry. The procedure involves taking thousands of high-speed, high-resolution snapshots.

Using this technique in 1995, scientists witnessed the disappearance of a star that was, at the time, the closest object to the black hole.

Whether the star was sucked into the black hole, or simply went behind it, scientists may never know.

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