(keynote speaker)

Testing black holes and compact objects with shadow observations

The imaging, via its accretion flow, of the central supermassive objects at the heart of the M87 and Milky Galaxies by the Event Horizon Collaboration, has proven the viability of the research field typically dubbed as shadows to test the strong-field regime of the gravitational interaction. In this keynote talk I will provide a succinct overview of the new possibilities raised in this context, from null tests of the Kerr hypothesis to explore alternative black hole geometries and horizonless compact objects. In particular, I will discuss the entanglement between background geometries and accretion flow in generating the photon rings and central brightness depression observed in the images, and possible ways out of this problem currently under discussion in the literature.