Researchers have presented a study in which they characterize the different states of activity of a large sample of supermassive black holes in active nuclei of galaxies.
For this they have compared their behavior with that of their closest relatives, stellar black holes in X-ray binaries.
Understanding the cycles of activity of black holes from a global perspective, which includes both objects with masses from a dozen suns to those with hundreds or billions of solar masses, is a paradigm that has been investigated for decades.
The former reside in binary systems together with a companion star from which they extract the gas necessary to sustain their activity, while the latter are found in the center of most galaxies and feed on the gas, dust and stars that they are trapped in the gravitational well of the galactic nucleus.
Stellar-mass black holes evolve rapidly. Their cycle of activity usually covers a few months or years, during which they go through various states or phases. These are characterized by changes in the properties of the accretion disk (where hot gas accumulates before falling into the black hole), the wind, and the jets of matter they produce.
There are two main states dominated by the accretion disk in one case and the jet in the second. The ‘soft’ state is marked by the thermal emission of the plasma in the disk, while the jet is observed in the ‘hard’ state, when the disk cools and the radio wave emission becomes very intense.
Due to their larger size, supermassive black holes evolve much more slowly than their stellar-mass counterparts. Therefore, demonstrating the existence of states and transits in each of these systems would imply monitoring for millions of years, so that these processes are imperceptible in the course of a human life.
On the other hand, the nuclei of galaxies are densely populated regions where the emission of stars and the absorption of light caused by hydrogen and dust mask and hide the radiation from the accretion disk around the central black hole.
For this study, astrophysics have used a large sample of 167 active galaxies that allows the possible states of accretion to be statistically identified in the population of supermassive black holes.
The emission from the accretion disk is not directly accessible, but the gas located in the central region of these galaxies absorbs and reprocesses the radiation in the form of spectral lines. Using the oxygen and neon lines seen in the mid-infrared range, it is possible to probe for the presence of the disk in these objects.
Presence of accretion states
The study demonstrates the presence of accretion states in supermassive black holes with properties very similar to those we know in stellar-mass black holes, where systems in the ‘soft’ state host a bright disk and those in the ‘hard’ state they show an intense radio broadcast, while the disc is very weak .
This work opens a new window to understand the behavior of matter (gas) when it falls into black holes of a wide range of masses and helps to understand precisely what are the cycles of activity of supermassive black holes that are located in the center of each galaxy .