University of Chile | 2018 Sep 04
A group of researchers led by Paula Sánchez-Sáez and Paulina Lira ... managed to determine that the rate of variability in the light emitted by material being swallowed by supermassive black holes in nuclei of active galaxies is determined by the accretion rate, that is, how much matter they are “eating.”
“The light emitted by the material that is falling (its brightness) changes a lot over time, without a stable pattern, so we say that they show variability. We know that it varies, but we still do not know clearly why. If one observes other objects, such as stars or galaxies without active nuclei, their brightness is constant over time, but if we look at galaxies with active nuclei their brightness rises and falls, and is completely unpredictable. We studied how the amplitude of this variation in the emitted light (or in simple words, the amplitude of the variability) is related, with the average luminosity emitted by the AGN, the mass of the super massive black hole, and the AGN accretion rate (which corresponds to how much material the black hole consumes in a year). The results of our analysis show that, contrary to what was believed, the only important physical property to explain the amplitude of the variability is the AGN accretion rate,” explains Paula Sánchez-Sáez.
The study determined that there is only one physical property that could predict the variability of these objects: the accretion rate. “This is nothing but how much material is falling into this supermassive black hole. So if it is on a diet, or if it is swallowing a lot or if it does not fit anymore in his mouth...that will determine if they vary much or little. And what we detect is that the less they swallow, the more they vary,” explains Paulina Lira ...
The QUEST–La Silla AGN Variability Survey: Connection between AGN
Variability and Black Hole Physical Properties ~ P. Sánchez-Sáez et al