Echo mapping the gravitational potential well of black holes
Black holes are the most extreme objects found in the universe. They provide a one-way passage to the unknown, places where our understanding of physics breaks down. Pioneering work over the last century has transformed black holes from theoretical curiosities, into the domain of the observational astronomer. These gravitational monsters reside in the centre of all galaxies in the universe, and are intimately linked to the formation and evolution of stars and galaxies we observe today. Despite their enormous size, our current telescopes are unable to spatially resolve them on the sky. We therefore resort to indirect methods to zoom in on the region directly around the black hole. In this talk, I will describe current efforts to spatially map the gas in the immediate vicinity of a black hole as it spirals down the deep gravitational potential well. These observations provide us with information about the two fundamental properties of black holes: their mass and spin.