New evidence of black hole at Milky Way's center
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.