The first image of a black hole

I will briefly discuss how the first image of a black hole was obtained
by the EHT collaboration. In particular, I will describe the theoretical
aspects that have allowed us to model the dynamics of the plasma
accreting onto the black hole and how such dynamics was used to generate
synthetic black-hole images. I will also illustrate how the comparison
between the theoretical images and the observations has allowed us to
deduce the presence of a black hole in M87 and to extract information
about its properties. Finally, I will describe the lessons we have
learned about strong-field gravity and alternatives to black holes.