Galaxy Center in X-rays

The Nearest Supermassive Black Hole Found?

CHANDRA PRESS RELEASE, JANUARY 14, 2000: Culminating 25 years of searching by astronomers, researchers at the Massachusetts Institute of Technology say that a faint X-ray source, newly 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. This X-ray source is the bright point at the center of the image above. The Chandra image shows that this source is embedded in extended hot gas produced by supernovae or stellar winds from massive stars, and is surrounded by other point sources of X-ray emission. Frederick K. Baganoff and colleagues from Pennsylvania State University, University Park, and the University of California, Los Angeles, presented their findings in Atlanta 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 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. 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. "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 satelllite," Baganoff said. Sagittarius A*, which stands out on a radio map as a bright dot, was detected at the dynamical center of the Milky Way galaxy by radio telescopes in 1974. Optical telescopes such as the Hubble Space Telescope cannot see the center of our galaxy, which is enshrouded in thick clouds of dust and gas in the plane of the galaxy. However, hot gas and charged particles moving at nearly the speed of light produce X-rays that penetrate this shroud. Only a few months after its launch, Chandra accomplished what no other optical or X-ray satellite was able to do: separate the emissions from the surrounding hot gas and nearby compact sources that prevented other satellites from detecting this new X-ray source. Chandra's ACIS detector was conceived and developed for NASA by Penn State University and MIT under the leadership of Penn State Professor Gordon Garmire.

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Page Author: Dr. Michael F. Corcoran
Last modified June 14, 2001