UPPER LIMIT OF 3.3 ASTRONOMICAL UNITS TO THE DIAMETER OF THE GALACTIC-CENTER RADIO-SOURCE SGR-A

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 accr eting onto a massive black hole. In observations at long wavelengths, the apparent angular size of Sgr A decreases in the manner expected f or emission from a point source scattered by electron density fluctuat ions along the line of sight. Measurements at a wavelength of 7 millim eters with the nearly completed Very Long Baseline Array indicate a si ze of 0.7 milliarc seconds, which is consistent with an extrapolation from results at longer wavelengths. The true size of Sgr A must be le ss than 0.4 milliarc seconds, or 3.3 astronomical units. The inferred black hole mass is less than 1.5 x 10(6) solar masses according to a r ecent model for the emission.