The Discovery of Sgr A*

Abstract

The discovery of the point-like radio source at the center of the Galaxy, colloquially termed Sgr A*, was made in February 1974 by Balick and Brown using the then-new 35km baseline interferometer between Green Bank and a remote site near Huntersville, WV. The highly unusual properties of the radio source are now well studied; however, the story behind the discovery is equally interesting. Although the signal from the source was strong (∼0.5 Jy) and the peak measured surface brightness quite high (∼107K), the interpretation of the signal as a single point source was initially obscured by the odd geometry of the synthesized aperture. In addition, two groups unknowingly competed to make the detection observations, both based on very different scientific rationales. The other group, comprising Downes and Goss, correctly anticipated the astronomical significance of the discovery but could not make their way from Europe to Green Bank when their observations were scheduled in the fall of 1973.