Upper limit of 3.3 astronomical units to the diameter of the galactic center radio source sgr a*

Abstract

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 10(6) solar masses according to a recent model for the emission.