Astronomers scanning the universe for active black holes sometimes overlook the suspected black hole lying quietly in the center of their own galaxy. But this week, a new study has the Milky Way and our hometown black hole at the center of attention.

Working with the Keck Telescope in Hawaii, researchers Andrea Ghez and her colleagues at the University of California at Los Angeles (UCLA) have yielded the best proof yet that a source of radio waves known as Sagittarius A* (Sgr A*, pronounced Sagittarius A Star) is in fact the Milky Ways resident black hole.

Using images snapped over a period of four years, the team found that the acceleration of several stars moving near Sgr A* are comparable in speed to the rate of Earth orbiting the sun. This find, which has been published in this weeks Nature, suggests that the stars are in fact orbiting around Sgr A*, which appears to have a gravitational pull comparable to that of a black hole.

"The holy grail recently was to acknowledge that we should see these stars turning in their orbits, and indeed this year we saw significant acceleration for curvature in the orbits," said Mark Morris, a member of the UCLA research team. "These accelerations tell us where the black hole must be and the location agrees very well with that of the radio source that has long thought to be a black hole, Sagittarius A*." 

American and European astronomers have been working on the problem of the Milky Ways black hole for a number of years. While they have suspected for some time that a supermassive black hole an immensely dense area of space that sucks up matter and light lies at the galaxys center, the culprit has not been easy to pin down.

In the last couple of years, European astronomers led by Reinhard Genzel have been able to estimate the mass of a large region of dark matter associated with the Sgr A* source. This dense region, which is now suspected to be the galaxys black hole, weighed in at more than 2.6 million times that of our sun extremely heavy considering it covers a total area no larger than that of Mars orbit around the sun.

Yet despite this strong evidence for a black hole, precise data about its exact location have eluded both the European and American teams. Now, it seems that the UCLA researchers may have caught the massive object dead in its tracks.

Ghez and her colleagues have all but pinpointed the black hole using a technique in which many images of the galaxys center are snapped and then later combined. Studying the groups latest images, which were taken between 1997 and 1999, the astronomers are then able to track the motion of several stars orbiting very close to the galactic center.

The observed stars were seen to be spiraling around Sgr A* at speeds of many hundreds of miles (kilometers) per second. Laws of physical mechanics maintain that at those speeds, the stars must be orbiting something with an incredibly large gravitational pull. Whats more, by tracking the stars acceleration and orbital paths, researchers can determine the center of the mass with a very high precision.

"One can now rule out just about any other form for the dark matter other than a black hole," said Fulvio Melia, a researcher and astronomy professor at the University of Arizona.

Recently, space telescopes like the Chandra X-ray Observatory and the Hubble Space Telescope have offered up beautiful glimpses of deep-space galaxies where very active black holes are thought to reside. But many researchers believe that Milky Ways black hole, though it is relatively quiet, remains an important object for astronomers to study because it is so close to home.

"The fact that the galactic center is in our cosmic backyard means that we can study our black hole with a precision that will never be attained with any other black hole," said Melia.

Today, astronomical techniques are so advanced and studies on Sgr A* are so common, we may soon even be able to see the holes event horizon -- the circular boundary beyond which matter gets sucked into a black hole. Researchers are also interested in finding out whether the object has an accompanying accretion disk of matter like those known to exist around very active black holes.

"This is one of the most rapidly exploding fields in astrophysics," said Melia. "Its going to dominate the literature probably for the next 10 years."