The galactic center data actually proved there was a supermassive black hole at the center of the Milky Way, and weighed it precisely from those stars motions. The name of the account that posted that animation (Sagittarius A*) is the name of that supermassive black hole.
This work earned the 2020 Nobel Prize in Physics: https://www.nobelprize.org/prizes/physics/2020/summary/
Can you explain the past tense "there was" ? Is there a reason for a black hole to dissapear?