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Active Galactic Nuclei
Galaxies host at their centre a supermassive black hole millions of times the mass of the sun. These objects have a significant impact on the evolution of the galaxy, especially due to the tremendous energy released while accreting matter. However the geometry of that immediate environment of accreting active black holes (also known as Active Galactic Nuclei, or AGN), is not fully understood yet.
The X-rays from the AGN spread out and illuminate the surrounding material, making it re-emit as UV and optical radiation. By measuring the delay between UV and optical emission and the X-rays, we can measure the distances between the central black hole and the surrounding re-emitting, or 'reverberating' material. Hence this technique is known as 'reverberation mapping' and is very similar to sonar mapping.
In recent years, astronomers (including me!) have started to monitor the strong variability from the light in these extreme objects in order to study the variability of these sources in many different telescopes. These include the Space X-ray UV/optical telescope, Neil Gehrels Swift Space Observatory and a global network of robotic telescopes, such as the Zowada and Las Cumbres Observatories.
These observations completely redefined our view of the surroundings of super massive black holes. While the main model for these objects indicated the presence of a thin accretion disc, illuminated by a compact very hot cloud of gas, these observations showed that the geometry is may more complex and dynamical.
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