When was the first evidence found for the accelerating rotation of the Milky Way’s center?

During the 1990s, astronomers using infrared telescopes began tracking stars near the Milky Way’s center with enough precision to show they were orbiting a massive invisible object. Continued observations pointed to Sagittarius A*, the supermassive black hole at the galaxy’s center. By measuring the orbits of stars such as S2, astronomers demonstrated that the central mass was compact and enormous. These studies became some of the strongest evidence for a supermassive black hole in our own galaxy.