Into the Cores of Luminous Galaxies: Echoes from Supermassive Black Holes

Unlike our own galaxy, the Milky Way, there exist many other galaxies in the universe whose centres shine with extraordinarily high energy—sometimes 10 to even 1,000 times
more luminous than the entire Milky Way. These are known as active galaxies, and scientists believe that this intense energy is powered by the gravitational potential energy of a supermassive black hole at their cores. The closest example of such an active galaxy is Centaurus A, located about 12 million light-years from Earth. At its centre lies a supermassive black hole weighing about fifty million times the mass of our Sun. In my talk, I will take you on a journey into the very central regions of these energetic galaxies— the regions so compact that, with current imaging techniques and modern telescopes, we can directly observe only a handful of the nearest ones. To overcome this limitation, we rely on a method
known as light echo-mapping, or reverberation mapping. This technique leverages a unique property of active galaxies: their natural flux variability over time. By analyzing how different regions around the black hole respond to changes in light, we can probe their structure and distances, much like using echoes to map out a dark room. I will also briefly explain how we estimate the mass of these supermassive black holes, and how we study the structure and motion—or kinematics—of the gas and dust swirling in their immediate surroundings.