Fredagskollokvium: Attempts to shed light on the dark lives of supermassive black holes

There is a strong interest in understanding how supermassive black holes form and grow because of indications that these black holes have a significant influence on their environment. A key parameter for detailed investigations of these issues is the prime property of the black hole, namely its mass. However, such investigations are somewhat hampered by the uncertainties in current mass measurements. I will summarize what we have learned so far and our efforts to improve the mass determinations in order to enable precision cosmology studies in the future. If there is time, I will discuss recent results of an ongoing study of an active galactic nucleus that a few years back suddenly turned off. However, it is not 'dead' and remains dormant. This is a very rare event that we hope can provide significant insight on how supermassive black holes feed and perhaps on the elusive structure of the black hole powered central engine of active galactic nuclei.