On April 10, 2019, the researchers of the Event Horizon Telescope revealed to humankind the first image ever obtained of a supermassive black hole, a black hole much more massive of normal stellar black holes. The image uncovers the black hole at the centre of a huge galaxy in the nearby Virgo cluster, Messier 87. This black hole is 55 millions light-years away from us, and a mass of 6.5 and a half billions times the one of the Sun.
Black holes are extremely compact objects, in which an incredible quantity of mass is compressed within a small region. The presence of these objects affects the surrounding environment, distorting space-time, and overheating any material there around. The gravitational attraction is so strong, that not even light manages to get out from a black hole: that is why it is called in this way! However, if it is surrounded by a very hot gas disk, we can recognize it, from its shadow, and manage to realize a few thing, for examples its mass.