Describe the evidence indicating that a black hole may be at the center of our Galaxy.

The most compelling evidence consists of recorded stellar tracks within 1 arcsecond (0.13 light-years) of the galactic center, whose orbital periods and radii indicate the presence of a central source of gravity having a mass equivalent to more than 4 million Suns, yet being concentrated within a radius less than 17 light-hours. Other evidence includes unique radio and X-ray emissions from the galactic center