The Supermassive Black Hole at the Galactic Center

Details The Supermassive Black Hole at the Galactic Center The Supermassive Black Hole at the Galactic Center

Jun 2002

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002aas...200.8407m&link_type=abstract

American Astronomical Society, 200th AAS Meeting, #84.07; Bulletin of the American Astronomical Society, Vol. 34, p.951

Astronomy and Astrophysics

Astronomy

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Scientific paper

Most of the dark matter at the Galactic center is concentrated within 0.015 pc, and is coincident with the radio point source Sgr A*. The evidence now points to this being a 2.6 million solar-mass object. Sgr A*'s mm/sub-mm spectrum and polarimetric properties, and its quiescent-state X-ray flux density (measured by Chandra), can be understood in the context of a model in which low angular momentum gas captured at large radii circularizes to form a hot, magnetized Keplerian flow within tens of Schwarzschild radii of the black hole's event horizon. This picture seems to have been confirmed by Chandra's recent detection of a three-hour X-ray flare from Sgr A*, which limits the size of the X-ray emitting region to a mere 20 Schwarschild radii. However, whereas Sgr A*'s quiescent X-ray emission appears to be produced by self-Comptonization (SSC) of the mm/sub-mm synchrotron photons, the prominent X-ray flare seen in Sgr A* is probably due to a sudden enhancement of accretion through the circularized region, which greatly enhances its bremsstrahlung emissivity. The considerable flattening of the spectrum seen during the flare by Chandra may thus signal a change in the dominant high-energy emission mechanism. This research was supported in part by NASA grants NAG5-8239 and NAG5-9205.

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