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New evidence of black hole at Milky Way's center

Quicktime Video

Animation showing the suspected black hole known as Old Faithful
devouring a companion star and erupting
1.5M/22 sec./240x180
753K/22 sec./160x120

January 7, 1998
Web posted at: 10:03 p.m. EST (0303 GMT)

WASHINGTON (CNN) -- A massive black hole, with a mass 2.6 million
times that of the sun, sits at the center of our Milky Way galaxy,
providing its gravitational anchor, according to new evidence
unveiled by astronomers Wednesday.

Research teams in Germany and the United States found that some
stars near the black hole, named Sagittarius A, are speeding along
at more than 600 miles a second -- nearly 2.2 million miles per hour
(3.5 million kph).

"This is the strongest case we have yet for a super, massive black
hole at the center of the Milky Way," said astronomer Andreas Eckart
at a news conference sponsored by the American Astronomical Society.

Sagittarius A is about 26,000 light years from our sun and the
planets that revolve around it. A light year is about 6 trillion
miles (9.6 trillion km).

A black hole is an entity of such density and gravitational strength
that nothing -- not even light -- can escape from its grasp. Because
it doesn't reflect light, a black hole cannot be seen and can only
be detected by measuring the motion of stars, gas and dust nearby.

The theory that a black hole exists in the center of the Milky Way
-- the galaxy in which Earth is located -- has long been
controversial, and many astronomers have rejected previous evidence
supporting such a theory.

But researchers at Wednesday's news conference said the latest data
bolsters the idea of a black hole because that is the best
explanation for their findings.

Old stars zip around Sagittarius A

Astronomers at the Harvard-Smithsonian Center for Astrophysics used
radio telescopes to make independent measurements of the motion of the
object at the center of the galaxy. They found that it stood relatively
still compared to the rest of the galaxy -- which is consistent with a
black hole.

Another team of researchers at the Max Planck Institute for
Extraterrestrial Physics in Germany found that thousands of stars
existed in the area around the black hole, zipping around in tight
circles. In order to cause stars to move that quickly, the black hole
would have to have 2.6 million times as much mass as our sun.

Many of the stars zipping around Sagittarius A are old -- "a retirement
village for stars," says Eckart -- suggesting that the black hole grows
more and more massive by sucking in stars over the eons and eventually
swallowing them.

Astronomers also unveiled evidence of another unusual black hole,
nicknamed Old Faithful, about 40,000 light years from Earth.

Old Faithful, more powerful the Sagittarius A, sucks matter into a
doughnut-like disk, then ejects it in eruptions that throw out an amount
of material as massive as Mount Everest at a speed of more than 171,000
miles per second (274,000 km per second.)

"It's incredibly violent," said Steven Eikenberry of the California
Institute of Technology. "We're talking about something that is
trillions of times the annual energy output of the United States."

And when the black hole is active, these eruptions take place in
consistent 30-minute intervals. Those regular eruptions led NASA
scientists to nickname the black hole after the Old Faithful geyser in
Yellowstone National Park, which also erupts regularly.

Reporter Rick Lockridge and Reuters contributed to this report.

Related stories:

Hubble images of dying stars force cosmic reconsideration -
December 17, 1997
Oooh! Ahhh! New cool pics from Hubble - June 9, 1997
With upgrade, Hubble offers new glimpse of space - May 12, 1997

Related site:

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Harvard-Smithsonian Center for Astrophysics
Max Planck Institute for Extraterrestrial Physics

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