In the center of the Messier 87 galaxy there is a massive black hole, which is currently being called Sagittarius A*. Before April 10th, we had never directly seen a black hole. Now we have a stunning, although somewhat blurry picture of Sagittarius A*.
What had stopped us from being able to see a black hole before April 10th is that black holes, despite their enormous mass, are actually very small. But now, thanks to an international collaboration of scientists and their Event Horizon Telescope (which is really 8 telescopes “paired” together), we have our picture.