Observers had been keeping close watch on the cluster since 2014, when they'd detected a supernova that turned out to be present in a galaxy 9 billion light years away. They realized Icarus was present in April 2016, when a point of light near the supernova seemed to change brightness.

Don't get too attached to this new discovery. With this kind of distance, Icarus has long-since turned into a neutron star or black hole. The findings are still advancing science in ways you might not expect, however. As the Guardian noted, the Icarus study ruled out a theory that dark matter consists of black holes. If that had been the case, they would have brightened Icarus even more. And if nothing else, this proves that humanity can detect more than just the largest and brightest celestial objects at these kinds of distances.