A team of scientists led by Frederick K. Baganoff of MIT detected a sudden X-ray flare while observing Sagittarius A*, a source of radio emission believed to be associated with the black hole at the center of our Galaxy.

"This is extremely exciting because it's the first time we have seen our own neighborhood supermassive black hole devour a chunk of material," said Baganoff. 

"This signal comes from closer to the event horizon of our Galaxy's supermassive black hole than any that we have ever received before. It's as if the material there sent us a postcard before it fell in."

At the peak of the flare, the X-ray intensity dramatically dropped by a factor of five within just a 10-minute interval. 

This constrains the size of the emitting region to be no larger than about 20 times the size of the "event horizon" (the one-way membrane around a black hole) as predicted by Einstein's theory of relativity.

The rapid rise and fall seen by Chandra are also compelling evidence that the X-ray emission is coming from matter falling into a supermassive black hole.

This would confirm the Milky Way's supermassive black hole is powered by the same accretion process as quasars and other active galactic nuclei.

Sagittarius A* is coincident with the location of this object, and is thought to be powered by the infall of matter into the black hole. However, the faintness of Sagittarius A* at all wavelengths, especially in X-rays, has cast some doubt on this model.

The latest precise Chandra observations of the crowded galactic center region have dispelled that doubt, confirming the results of the dynamical studies.

Given the extremely accurate position, it is highly unlikely that the flare is due to an unrelated contaminating source such as an X-ray binary system.

"It makes Sagittarius A* a uniquely valuable source for studying conditions very near a supermassive black hole."
The energy released in the flare corresponds to the sudden infall of material with the mass equivalent to a comet. 

Alternatively, the scientists speculate that this flare could have been caused by the reconnection of magnetic field lines just outside the event horizon, similar to phenomenon responsible for solar flares but on a tremendous scale.

A longer-term increase in radio emission was also observed beginning around the time of the flare, indicating that the production of high-energy electrons was increasing.

"It's truly remarkable that we could identify and track this flare in such a crowded region of space," said Mark Bautz of MIT. "This discovery would not have been possible without the resolution and sensitivity of Chandra and the ACIS instrument."

The team first observed Sgr A* with ACIS on September 21, 1999, and again on October 26-27, 2000. The X-ray flare was detected in the second observation.

Other members of the team are Niel Brandt, George Chartas, Eric Feigelson, Leisa Townsley (Penn State), Yoshitomo Maeda (Institute of Space and Astronautical Science, Japan), Mark Morris (UCLA), George Ricker (MIT), and Fabian Walker (CalTech).

The ACIS instrument was developed for NASA by Penn State and MIT under the leadership of Garmire. NASA's Marshall Space Flight Center in Huntsville, Ala., manages the Chandra program, and TRW, Inc., Redondo Beach, Calif., is the prime contractor for the spacecraft. 

The Smithsonian's Chandra X-ray Center controls science and flight operations from Cambridge, Mass.