Black Holes Surrounded by Massive Energy Harvesting Structures Could Power Alien Civilizations | Science

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Artist’s impression of a Dyson sphere surrounding a star

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By Ian Randall

On the longtime TV show Doctor Who, the aliens known as time lords drew their power from the captured heart of a black hole, which supplied their planet with energy and time travel technology. The idea has merit, according to a new study. Researchers have shown that very advanced alien civilizations could theoretically build megastructures called Dyson spheres around black holes to harness their energy, which can be 100,000 times that of our Sun. The work could even give us a way to detect the existence of these extraterrestrial societies.

“I like these speculations about what advanced civilizations might do,” says Tomáš Opatrný, a physicist at Palacký University in Olomouc, who was not involved in the work but agrees that a Dyson sphere around a hole black would provide its builders with a lot of power.

If humanity’s energy needs continue to grow, a time will come when our energy consumption will approach or even exceed the total energy available on our planet. This was argued by physicist Freeman Dyson in 1960. Borrowing from British science fiction author Olaf Stapledon, Dyson proposed that any sufficiently advanced civilization that wanted to survive would have to build massive structures around stars that could harness their power. energy.

Most of these Dyson spheres involve many satellites orbiting or sitting motionless around a star. (A solid shell totally enveloping a solar body – as envisioned in a Star Trek: The Next Generation episode – is considered mechanically impossible, due to the gravity and pressure of the central star.) Such mega-infrastructures should turn this solar energy into usable energy, a process that creates waste heat. This heat appears in the mid-infrared spectrum, and stars with an excessive infrared signal have become a key target in the search for alien life.

But National Tsing Hua University astronomer Tiger Hsiao says we may be looking for the wrong thing. In a new study, he and his colleagues attempted to calculate whether it would also be possible to use a Dyson sphere around a black hole. They analyzed black holes of three different sizes: these five, 20 and 4 million times the mass of our Sun. These, respectively, reflect the lower and upper limits of black holes known to have formed from the collapse of massive stars – and the even larger mass of Sagittarius A *, the massive supermassive black hole that would hide in the center of the Milky Way. .

Black holes are generally viewed as consumers rather than producers of energy. Yet their huge gravitational fields can generate energy through several theoretical processes. These include the radiation emitted by the gas build-up around the hole, the spinning “accretion” disc of matter slowly falling towards the event horizon, the relativistic jets of matter and energy that shoot along. of the hole’s axis of rotation, and Hawking radiation — a theoretical way that black holes can lose mass, releasing energy in the process.

From their calculations, Hsiao and his colleagues concluded that the accretion disk, surrounding gas, and black hole jets can all serve as viable energy sources. In fact, energy from the single accretion disk of a 20 solar mass stellar black hole could provide the same amount of energy as Dyson spheres around 100,000 stars, the team will report next month in the. Monthly notices from the Royal Astronomical Society. If a supermassive black hole were tapped, the energy it could provide could be even 1 million times greater.

If such technology is at work, there may be a way to spot it. According to the researchers, the waste heat signal from a so-called “hot” Dyson sphere – a Dyson sphere capable of somehow surviving temperatures above 3000 Kelvin, above the melting point of known metals – around A stellar-mass black hole in the Milky Way would be detectable at ultraviolet wavelengths. Such signals could be found in data from various telescopes, including NASA’s Hubble Space Telescope and Galaxy Evolution Explorer, Hsiao says.

Meanwhile, a “solid” Dyson sphere – operating below 3000 Kelvin – could be picked up in the infrared by, for example, the Sloan Digital Sky Survey or the Wide-field Infrared Survey Explorer. The latter is no stranger to researching infrared signals from traditional Dyson star-based spheres. But, like all other research of this type, it has yet to find anything conclusive.

Opatrný says that using the radiation from the accreting disks would be particularly smart, as the disks convert energy more efficiently than the thermonuclear reaction in conventional stars. Aliens concerned about the sustainability of their power supplies, he suggests, had better encapsulate small stars that slowly burn their fuel. However, he continued, “Fast-living civilizations feeding on black hole accretion discs would be easier to spot thanks to the enormous amount of waste heat they produce.”

Inoue Makoto, an astrophysicist at the Institute of Astronomy and Astrophysics Academia Sinica, says regular black holes could support so-called Type II civilizations, whose total energy needs match those of an entire star system. Supermassive black holes, he adds, could power Type III civilizations, whose power consumption would be equal to that emitted by an entire galaxy.

As to why aliens might be using this energy, Opatrný has some thoughts. “Mining cryptocurrency, playing computer games, or just feeding the ever-growing bureaucracy? He thought jokingly. Either way, maybe the Time Lords were on to something after all.


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