The researchers Juan A. Fernández-Ontiveros, of the Istituto Nazionale di Astrofisica (INAF) in Rome and Teo Muñoz-Darias, of the Instituto de Astrofísica de Canarias (IAC), have written an article in which they describe the different states of activity of a large sample of supermassive black holes in the centers of galaxies. They have classified them using the behavior of their closest "relations", the stellar mass black holes in X-ray binaries. The article has just been published in the journal Monthly Notices of the Royal Astronomical Society (MNRAS).