Upper Limit of 3.3 Astronomical Units to the Diameter of the Galactic Center Radio Source Sgr A*
D. C. Backer 1,
J. A. Zensus 2,
K. I. Kellermann 3,
M. Reid 4,
J. M. Moran 4, and
K. Y. Lo 5
1 Astronomy Department, University of California, Berkeley, CA 94720
2 National Radio Astronomy Observatory, Socorro, NM 87801
3 National Radio Astronomy Observatory, Charlottesville, VA 22903
4 Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02139
5 Astronomy Department, University of Illinois, Urbana, IL 61801
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.
Submitted on June 2, 1993
Accepted on October 15, 1993
