Originally created 01/08/98

New evidence for massive black hole at Milky Way's center



WASHINGTON (AP) -- Stars speeding 2 million miles an hour near the center of the Milky Way give the strongest evidence yet that a massive black hole is providing a gravitational anchor at the center of Earth's galaxy, astronomers said Wednesday.

By measuring the motion of two hundred stars in the Milky Way, researchers at the Max Planck Institute for Extraterrestrial Physics in Germany found that stars nearest the galaxy's center move the fastest, some speeding along at more than 600 miles a second.

Astronomer Andreas Eckart said he and his colleagues calculated it would take an object 2.6 million times more massive than the sun to cause the stars to move in such a fashion.

"This is the strongest case we have yet for a super massive black hole at the center of the Milky Way," Eckart said at a news conference of the American Astronomical Society. No other reasonable explanation can be found for the motion of the stars.

The concept that a black hole exists in the center of the Milky Way has long been controversial. Some earlier evidence was rejected by many astronomers.

Astronomers at the AAS meeting said, however, that the German findings and some American studies suggest powerfully the presence of a massive black hole at the galaxy's center.

"This is the best evidence yet," said Steve Maran, a NASA astronomer.

The center of the Milky Way is 26,000 light years from the sun and its planets, including the Earth.

Researchers at the Harvard-Smithsonian Center for Astrophysics used radio telescopes to make independent measurements of the sun's orbit of the galactic center and of the motion of Sagittarius A. As a reference, they used stellar objects in the background called quasars, beyond the galaxy.

Mark Reid said that if the object at the Milky Way's center is a black hole, then it would stay relatively still as the sun moves in its orbit.

Reid said two years of measurements show that Sagittarius A was virtually motionless, while the sun moved at half a million miles an hour in its 200-million-year orbit of the galactic center.

"This is totally consistent with there being a supermassive black hole" at the galactic center, Reid said.

Eckart said thousands of stars exist within an area just 200 times the size of the solar system clustered around the galactic center. Some of these stars are zooming at high speeds, zipping in tight circles about the center.

A speeded up simulation of the star motion resemble billiard balls rolling rapidly in many directions.

Reid said that most of the stars near the galactic center are very old.

"It is like a retirement village of stars," he said.

This suggests, said Eckart, that a "seed black hole" existed early in the Milky Way's history that over the eons has grown more and more massive as it swallowed stars.

A massive black hole is thought to be a point of such infinite density and gravitational strength that nothing can escape from its grasp. Even light is sucked into the hole. Thus, since it gives out no light, it cannot be seen.

Astronomers deduce the presence of such an object by measuring the motion of stars, gas and dust nearby. The more massive the object, the faster nearby objects will move as they zip past.