Computer Representation of the Stellar Motions in the Core of M4

This is a simulation of the motions of stars around a suspected black hole in the core of the globular cluster M4. It is based on the "HST Legacy Survey of Galactic Globular Clusters: Shedding UV Light on Their Populations and Formation,” which includes stellar clusters' internal kinematics. 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 1 light-year across. It is the sphere of influence of the putative intermediate-mass black hole. Estimated to be 800 solar masses, the black hole has an event horizon that is a little more than half the diameter of our moon. The sphere of influence of the black hole is the region where its gravitational potential dominates over the gravitational potential of the starfield. It is a region where stellar motions are significantly affected by the black hole's gravitational pull. Only Hubble's sharp resolution can plot this motion over more than a decade of observing. The fastest moving stars in this video are not in the cluster, but are much closer to us, in the foreground of Milky Way stars.