Dyson Sphere, Black holes surrounded by massive, energy-harvesting structures could power alien civilizations

The original series of Star Trek is an American sci-fi contextualization of starship USS Enterprise, a space exploration vessel built by the United Federation of Planets in the 23th century, on a mission "to explore strange new worlds, to seek out new life and new civilizations, to boldly go where no man has gone before".  totally watch it.

In 1960, Physics Freeman Dyson put forth a paper in Science that changed the way we talked about alien civilizations. In it, Dyson conjectured that a sufficiently advanced civilization would harness the power of its home star to generate power on a massive scale. He also proposed that nascent search for extraterrestrial intelligence (SETI) programs should “search for sources of infrared radiation” to “accompany the recently initiated search for interstellar radio communications.” 
These structures became known as Dyson spheres, and a handful of programs have sought them out by looking for weird infrared signatures around neighboring stars. But what if a more advanced extraterrestrial civilization is not only building megastructures that surround stars, but turning to the infamous beasts of the cosmos for energy: black holes. A recent paper published in Monthly Notices of the Royal Astronomical Society suggests that scientists should start to look for Dyson spheres around black holes as an indication of an alien civilization. 






What are Dyson spheres?

A Dyson sphere is a theoretical megastructure that surrounds a star to collect its energy output.
Dyson proposed the spheres as a solution to a growing alien civilization needing a large enough energy output to sustain its existence. They can accomplish this by using space-based stellar energy harvesting swarms.
Dyson’s based his proposal on the fact that a planet only receives a small fraction of the energy produced by its host star. About one one-billionth of the Sun’s total energy output actually reaches the Earth.
By creating a space-based structure, an alien civilization could meet the energy needs to push its civilization to the next level.

Can you build a Dyson Sphere around a black hole?

    The recent study suggests that instead of building a Dyson sphere around a star, a civilization can build the same megastructure around black holes. A black hole is a region of space with a gravitational pull so strong that nothing can escape its influence, not even light itself. Scientists believe that every major galaxy has a black hole lurking at its center.

The researchers behind the new study suggest that building a 

Dyson sphere around a black hole would allow an alien 

civilization to garner energy from six sources:

• The cosmic microwave background, electromagnetic radiation left over from the Big Bang.

• Hawking radiation, theoretical radiation released by the black hole.

• The accretion disk, a disk of material that orbits around a black hole.

• Bondi accretion, the spherical accretion of ionized gas around an object.

• A corona, a bright region of white light above a black hole that forms from hot gas particles. 

• Powerful jets of radiation and particles emitted from the black hole at nearly the speed of light.

By not only relying on radiation as the main source of energy but a Dyson sphere around a black hole would also collect five times as much energy as one around a star, according to the study.

    In the long-running TV show Doctor Who, aliens known as time lords derived their power from the captured heart of a black hole, which provided energy for their planet and time travel technology. The idea has merit, according to a new study. Researchers have shown that highly 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 Olomouc, who was not involved with the work but agrees that a Dyson sphere around a black hole would provide its builders with lots of power.
If humanity’s energy demands continue to grow, a point will come when our power consumption approaches, or even exceeds, the total energy available to our planet. So argued physicist Freeman Dyson way back in 1960. Borrowing from British sci-fi author Olaf Stapledon, Dyson proposed that any sufficiently advanced civilization that wanted to survive would need to build massive structures around stars that could harness their energy.

Can we detect Alien Dyson Sphere?

In 2015, astronomer Tabetha Boyajian spotted a mysteriously dim star, its light flickering irregularly in a way that scientists had never observed before.

Some scientists believed that the star, officially known as KIC 8462852 but later dubbed Boyajian’s Star, had a Dyson sphere built around it, which resulted in its strange dimming. The idea was later dismissed in favor of debris around the star, but it sparked a search for these megastructures.

“There are a few people who think about looking for them, they are looking for large structures that might pass in front of the star or anything else, but large things,” Jason Wright, a Penn State astronomer and director of the Penn State Extraterrestrial Intelligence Center, tells Inverse. “So if you think about (Boyajian’s) Star, and the way that it got dimmer and all of its weirdness [...] That's the sort of thing they're looking for, more of those.

    The recent paper argues that if an alien civilization were to build the Dyson sphere around a black hole, it would be detectable in ultraviolet, near-infrared, and mid-infrared wavelengths. But Wright suggests it might be exceedingly difficult.
“In general, that'd be harder to detect,” he says. “Or at least, harder to tell that it was a Dyson Sphere.”
Using current telescopes such as the Galaxy Evolution Explorer, an orbiting space telescope launched in 2003, the authors argue that one could detect such structure around a distant star.
Most of these Dyson spheres involve numerous satellites orbiting or sitting motionlessly around a star. (A solid shell totally encasing a solar body—as envisioned in a Star Trek: The Next Generation episode—is considered mechanically impossible, because of the gravity and pressure from the central star.) Such megastructures would have to transform that solar energy into usable energy, a process that creates waste heat. This heat shows up in the mid-infrared spectrum, and stars with an excess infrared signal have become a key target in the search for extraterrestrial life.

But astronomer Tiger Hsiao of National Tsing Hua University says we might be looking for the wrong thing. In a new study, he and colleagues set out 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: those 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 more enormous mass of Sagittarius A*, the supermassive massive black hole thought to lurk at the center of the Milky Way.

Black holes are typically thought of as consumers rather than producers of energy. Yet their huge gravitational fields can generate power through several theoretical processes. These include the radiation emitted from the accumulation of gas around the hole, the spinning “accretion” disk of matter slowly falling toward the event horizon, the relativistic jets of matter and energy that shoot out along 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 colleagues concluded that the accretion disk, surrounding gas, and jets of black holes can all serve as viable energy sources. In fact, the energy from the accretion disk alone of a stellar black hole of 20 solar masses could provide the same amount of power as Dyson spheres around 100,000 stars, the team will report next month in the Monthly Notices of the Royal Astronomical Society. Were a supermassive black hole harnessed, the energy it could provide might be 1 million times larger still.

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—one somehow capable of surviving temperatures in excess of 3000 kelvin, above the melting point of known metals—around a stellar mass black hole in the Milky Way would be detectible at ultraviolet wavelengths. Such signals might be found in the 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 looking for the infrared signals of traditional, star-based Dyson spheres. But, like all other such searches, it has yet to find anything conclusive.

Opatrný says using the radiation from accretion disks would be particularly clever, because the disks convert energy more efficiently than the thermonuclear reaction in conventional stars. Aliens concerned with the sustainability of their power supply, he suggests, might be better off encapsulating small stars that burn their fuel slowly. However, he continued, “The fast-living civilizations feeding on black hole accretion disks would be easier to spot from the huge amount of waste heat they produce.”

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