Final answer:
Observational evidence supports the existence of a supermassive black hole at the center of the Milky Way galaxy.
Step-by-step explanation:
Observational evidence supports the existence of a supermassive black hole at the center of the Milky Way galaxy. Researchers from the UCLA Galactic Group analyzed the orbits of stars near the galactic center using data from the W. M. Keck telescopes. These observations revealed that approximately 4 million solar masses are concentrated in a small volume, about the size of Mercury's orbit. Other observations with the Hubble Space Telescope and ground-based telescopes have also provided evidence for the presence of supermassive black holes in the centers of other galaxies.