Dyson spheres are theoretical megastructures that advanced civilizations could use to extract as much energy as possible from a star. Researchers have now asked: would you get much energy if you were to build something like this around a black hole? The answer is a resounding yes.
Black holes, in their stellar-sized or supermassive version, don’t let anything escape – not even light. However, they create some of the most extreme conditions in the universe, and extremely energetic processes take place around black holes. For the paper, published in Monthly Notices of the Royal Astronomical Society, those processes would justify the construction of a Dyson sphere.
The research team, led by astronomer Tiger Yu-Yang Hsiao of National Tsing Hua University in Taiwan, looked at the possible emission from the accretion disk around a black hole, its corona, and even relativistic jets emitted by the black hole.
All those phenomena are extremely energetic. If an advanced civilization were capable of harnessing them, it would certainly not have to worry about its energetic needs for a while. In the paper, the focus is on a Type II civilization of the Kardashev Scale which can harness about one trillion times the energy that humanity has used in 2020. With that in mind, a Dyson sphere around a black hole is the most efficient solution.
“Usually, accretion disks can provide 10,000 and even more times the energy you would get from a star like the Sun,” Hsiao told IFLScience. “So instead of hunting 10,000 stars like our Sun, we can just find one black hole and build a Dyson sphere around it and it would be much more efficient.”
Hsiao’s approach looks at the energy output and provides some scenarios on how efficient a system has to be to get plenty out. By their very nature, black holes are so mind-boggling that even grabbing a fraction of their output would last our civilization billions of years.
The paper doesn’t discuss the feasibility of such a structure. A solid Dyson sphere is seen as an impossibility – but a Dyson swarm, with a large number of satellites doing the energy collection, seems much more realistic. However, to increase efficiency, they ought to be closer to the black hole and able to withstand much higher temperatures than the technology we can currently employ.
We can’t do it, but maybe there are alien civilizations out there that can. And the good news is that if such a structure exists in the Milky Way, we can detect it – although much more work would it be necessary to confirm it was an artificial source.
“We need other evidence to classify and distinguish these sources from other natural phenomena,” Hsiao told IFLScience. “We also propose other methods such as measuring the light curves and radial velocity. If there’s a Dyson sphere in a satellite form it will rotate, move in front of the black hole and behind the black hole and the light curve will change.”
And maybe we could spot something beyond our galaxy, as a more advanced civilization could do have the same approach but around a supermassive black hole.
Hsiao, who’s responsible for the vast majority of this work, is already looking at actual galactic surveys and producing models of what such structures might actually look like, to maybe help astronomers identify these Dyson swarms if they exist out there.