Upper Limit of 3.3 Astronomical Units to the Diameter of the Galactic Center Radio Source Sgr A*

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Science  26 Nov 1993:
Vol. 262, Issue 5138, pp. 1414-1416
DOI: 10.1126/science.262.5138.1414


Sagittarius (Sgr) A* is a unique radio source located at the center of our galaxy. The radiation from Sgr A* may be generated in matter accreting onto a massive black hole. In observations at long wavelengths, the apparent angular size of Sgr A* decreases in the manner expected for emission from a point source scattered by electron density fluctuations along the line of sight. Measurements at a wavelength of 7 millimeters with the nearly completed Very Long Baseline Array indicate a size of 0.7 milliarc seconds, which is consistent with an extrapolation from results at longer wavelengths. The true size of Sgr A* must be less than 0.4 milliarc seconds, or 3.3 astronomical units. The inferred black hole mass is less than 1.5 x 106 solar masses according to a recent model for the emission.