Dyson spheres around black holes could reveal alien civilizations, scientists say


One of the biggest questions we ask ourselves about the Universe is: are we alone as a technologically advanced species? This raises further questions: If there were aliens, what would their technology look like? And, of course, how could we detect it?

A new study has provided some answers to these questions – at least if the technology in question is a type of insane energy collector called a Dyson sphere, drawing energy from a black hole.

“In this study, we consider an energy source from a well-developed Type II or Type III civilization. They need an energy source that is more powerful than their own sun,” the researchers write in their paper. .

“An accretion disk, corona, and relativistic jets could be potential power plants for a Type II civilization. Our results suggest that for a stellar mass black hole, even at a low Eddington ratio, the disk d ‘accretion could provide hundreds of times more luminosity than a main sequence star. “

The concept of Dyson’s sphere was popularized by theoretical physicist Freeman Dyson in the 1960s as a solution to the problem of energy consumption beyond the capabilities of a civilization’s planet. The sphere itself is built around the star of the planetary system – a megastructure that harvests the star’s energy at the source.

The Dyson paper proposed that infrared emissions of thermal energy could escape as Dyson’s structure captures and converts stellar energy, which could hypothetically reveal the presence of these hypothetical structures. This infrared signature, if we could detect it, would allow us to spot extraterrestrial civilizations.

Led by astronomer Tiger Yu-Yang Hsiao of National Tsing Hua University in Taiwan, a team of researchers took the concept even further. What if the Dyson sphere (or the Dyson ring or the Dyson swarm) was arranged around a black hole? Would it work, and what would we be able to detect, from here on Earth?

The only thing black holes are known for is their powerful gravitational field that absorbs anything that gets close enough and doesn’t let it go out (which we can detect).

So you might be wondering how to harvest anything of such a beast. It turns out that there are a number of processes in the extreme environment about a black hole from which energy could possibly be harvested.

In their paper, the team considers a number of these processes: the accreting disk of matter swirling around a black hole, frictionally superheated to millions of degrees; Hawking radiation, the theoretical black body radiation emitted by black holes proposed by Stephen Hawking.

Other potentially relevant phenomena that could contribute include spherical accretion, the ring of magnetized plasma between the inner edge of the accretion disk and the event horizon, and jets launched at relativistic speeds from the poles of black holes. active.

Based on models of black holes clocked at 5, 20 and 4 million times the mass of the Sun (which is the mass of Sagittarius A *, the supermassive black hole at the heart of the Milky Way), Hsiao and his colleagues were able to to determine that a sphere of satellites would be able to efficiently harvest the energy of some of these processes.

“The greatest luminosity can be collected from an accretion disk, reaching 100,000 times the luminosity of the Sun, enough to maintain a Type II civilization,” the researchers write.

“Additionally, if a Dyson sphere collects not only electromagnetic radiation but also other types of energy (eg, kinetic energy) from the jets, the total energy collected would be about five times as much.”

Such structures would be detectable at multiple wavelengths, the researchers found, with hotter Dyson spheres more visible in the ultraviolet and cooler Dyson spheres visible in the infrared, much like Dyson itself. ‘had predicted.

However, since active black holes already emit a lot of radiation in these two wavelength ranges, detecting excess Dyson might be easier said than done.

The team suggests that taking other measurements, such as changes in light as the black hole is minutely affected by the gravity of the sphere, could help reveal where these structures might be hiding.

The research was published in the Monthly notices from the Royal Astronomical Society.

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