I think at least once in a lifetime everyone has thought about whether we are alone in the universe. Many others arise from this question: if aliens exist, what will they look like? Will we have something in common with them? Will we be able to adopt technology from them? Well, one of the main questions is how could we find a highly developed civilization?
It is interesting not only because of the fact that it is possible to detect another civilization, but also because we could understand whether we correctly predicted the development paths of civilizations.
I think so, everyone who is interested in the topic has heard about the Kardashev scale. This scale assumes the presence of seven types of civilizations in the Universe and, according to a new study, we could try to find civilizations of the second or third type, since they need a more powerful source of energy than their own Sun.
This is where a hypothetical structure for storing energy from a source, called the "Dyson sphere", comes to the rescue. The authors of the work assume that the designated civilizations will be able to collect the energy of black holes of stellar mass.
How is this supposed to work and can we detect such a structure?
It would seem that a black hole absorbs material around it, having a powerful gravitational field, but it turned out that in an extreme environment around a black hole there are a number of processes from which it may be possible to extract energy.
According to the authors of the work, the accretion disk alone can provide hundreds of times more luminosity than a main sequence star.
The corona of magnetized plasma between the inner edge of the accretion disk and the event horizon, as well as jets emitted at relativistic velocities from the poles of black holes, are an equally suitable source of energy that a type II civilization is quite capable of curbing.
Will we be able to detect such structures?
This question turned out to be even more complicated. The researchers showed that such structures can be detected at several wavelengths, with hotter Dyson spheres being better visible in the ultraviolet range, and colder ones in the infrared, as Dyson himself predicted.
True, they immediately correct themselves. The fact is that active black holes emit so much radiation in both of these wavelength ranges that it is almost impossible to detect a certain technological structure against their background.
But this adds an explanation to the Fermi paradox. In the case of the existence of more advanced civilizations, we cannot detect them precisely because we do not have the appropriate tools. So even their vigorous activity is simply beyond our field of vision.