Chandra Discovers X-ray Source at Center of Our Galaxy

January 14, 2000

Atlanta, Ga. --- Culminating 25 years of searching by astronomers, researchers at Massachusetts Institute of Technology say that a newly detected, faint X-ray source detected by NASA's Chandra X-ray Observatory may be the long-sought X-ray emission from a known supermassive black hole at the center of our galaxy.

Dr. Frederick K. Baganoff, and colleagues from Penn State and the University of California, Los Angeles, will present their findings today (Jan. 14) at the 195th national meeting of the American Astronomical Society.

Baganoff, lead scientist for the Chandra X-ray Observatory's Advanced CCD Imaging Spectrometer (ACIS) team's "Sagittarius A* and the Galactic Center" project and a postdoctoral research associate at MIT, said that the precise positional coincidence between the new X-ray source and the radio position of a long-known source called Sagittarius A* "encourages us to believe that the two are the same." Sagittarius A* is a point-like, variable radio source at the center of our galaxy. It looks like a faint quasar and is believed to be powered by gaseous matter falling into a supermassive black hole with 2.6 million times the mass of our sun.

Chandra's remarkable detection of this X-ray source has placed astronomers within a couple of years of a coveted prize: measuring the spectrum of energy produced by Sagittarius A* to determine in detail how the supermassive black hole that powers it works.

"The race to be the first to detect X-rays from Sagittarius A* is one of the hottest and longest-running in all of X-ray astronomy," Baganoff said. "Theorists are eager to hear the results of our observation, so they can test their ideas."

But now that an X-ray source close to Sagittarius A* has been found, it has taken researchers by surprise by being much fainter than expected. "There must be something unusual about the environment around this black hole that affects how it is fed and how the gravitational energy released from the infalling matter is converted into the X-ray light that we see," said Baganoff. "This new result provides fresh insight that will, no doubt, stir heated debates on these issues."

"Chandra's sensitivity is 20 times better than achieved with the best previous X-ray telescopes," said Gordon Garmire, the Evan Pugh Professor of Astronomy and Astrophysics at Penn State and head of the team that conceived and built Chandra's Advanced CCD Imaging Spectrometer (ACIS) X-ray camera, which acquired the data. "This sensitivity, plus the superior spatial resolution of Chandra's mirrors, make Chandra the perfect tool for studying this faint X-ray source in its crowded field."

"The luminosity of the X-ray source we have discovered already is a factor of five fainter than previously thought, based on observations from an earlier X-ray satellite," Baganoff said. "This poses a problem for theorists. The galactic center is a crowded place. If we were to find with further study that most or all of the X-ray emission is not from Sagittarius A*, then we will have shown conclusively that all current models for Sagittarius A* need to be rethought from the ground up."

Astronomers believe that most galaxies harbor massive black holes at their centers. Many of these black holes are thought to produce powerful and brilliant point-like sources of light that astronomers call quasars and active galactic nuclei. Why the center of our galaxy is so dim is a long-standing puzzle.

For a longer version of this story, go to: http://www.science.psu.edu/alert/Baganoff1-2000.htm To follow Chandra's Progress or download images visit the Chandra sites at http://chandra.harvard.edu and http://chandra.nasa.gov

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Contacts: Deborah Halber; Massachusetts Institute of Technology, 617-258-9276;

Steve Roy; Marshall Space Flight Center, Huntsville; Ala., 256-544-6535; http://www.msfc.nasa.gov/news

Dr. Wallace Tucker; Chandra X-ray Observatory Center; CFA, 617-496-7998

Barbara Kennedy; Penn State PIO; 814-863-4682