 Here's another example of detecting a black hole by finding stars orbiting an invisible point. In 2023, a team of astronomers detected a possible intermediate-mass black hole of roughly 800 solar masses at the center of the M4 globular star cluster. They examined 12 years' worth of M4 observations from Hubble and resolved pinpoint stars. The suspected object can't be seen, but its mass is calculated by studying the motion of stars caught in its gravitational field. The black hole has an event horizon that is a little more than half the diameter of our moon. This is a simulation of the motions of stars around the suspected black hole. After the zoom into M4, the center of the cluster, where the suspected black hole resides, is highlighted by a red X. The red circle has a radius of a little less than one light year. It delineates the sphere of influence of the intermediate-mass black hole.