With every year that goes by, the total amount of knowledge that humanity accumulates only grows and grows. At the start of 2015, humanity had never detected a gravitational wave; at present, we’ve detected 11, and fully expect to find perhaps hundreds more in 2019. In the early 1990s, we didn’t know whether there were any planets outside our own Solar System; today, we have thousands, some of which are almost good enough to be considered Earth-like.
We’ve found all the particles in the Standard Model; we’ve discovered that the Universe is not only expanding, but accelerating; we’ve determined how many galaxies are in the Universe. But next year, something new and unprecedented is going to happen: we’re going to image a black hole’s event horizon for the first time. The data is already in hand; the rest is just a matter of time.
Black holes are fairly easy objects to detect, once you know what you’re looking for. It may seem counterintuitive, because they emit no light of their own, but they do have three surefire signatures that allow us to know that they’re there.