What we discovered is that the supermassive black holes at the center of galaxies and the galaxies themselves are really very tightly intertwined.
The stars at the edge of the galaxy have no physical connection with the black hole. Yet somehow their speed is tightly bound with the size of the black hole billions of miles away. If the two things aren't physically linked now, it means they must have been at some point in the past.
The fact that we see there is such a tight relationship between the speed of the stars and the black hole in the middle is a probe to what happened early on in the galaxy.
It screams at you something that you don't yet understand about the connection between galaxy formation and black hole formation.
The relationship points at an extraordinary idea: that galaxies and their giant black holes could be linked from birth. In fact, scientists thought that supermassive black holes might even be involved in the formation of galaxies themselves.