Technologically savvy aliens could be powering their society using a hypothetical megastructure called a Dyson sphere to harvest energy from a black hole. And the sphere might radiate in peculiar ways, allowing telescopes on Earth to discover the existence of intelligent beings elsewhere in the universe, a new study suggests.
A Dyson sphere is a speculative structure that would encircle a star with a tight formation of orbiting platforms in order to capture starlight and produce power, according to Live Science's sister site Space.com. First proposed by theoretical physicist Freeman Dyson in 1960, the idea might be realized by a spacefaring extraterrestrial species who had spread out across their star system and therefore required ever-increasing amounts of energy.
During a coffee break, astronomer Tiger Yu-Yang Hsiao of National Tsing Hua University in Taiwan and his colleagues read a paper about Dyson spheres and began wondering if it were possible to build one around a black hole instead of a star.
Hsiao said, black holes are one of the brightest objects in the sky. While we normally think of them as being dark and all-consuming, black holes can radiate incredible amounts of energy. The material often forms a disk as it falls into a black hole's maw, much like water circling a drain.
As the gas and dust in this disk spin and bump against each other, they heat up through friction, sometimes to millions of degrees, producing light in the X-ray portion of the electromagnetic spectrum, Hsiao said. Colossal beams of energy can also shoot from a black hole's poles.
Hsiao said, because black holes smoosh a gargantuan mass into a tiny area of space, they are smaller than stars and therefore potentially easier to encircle. A species that choose to build a Dyson sphere around a black hole can save a lot of material. Such a search might be useful no matter what it uncovers, Macy Huston, a doctoral candidate in astronomy at The Pennsylvania State University who was not involved in the work. Even if you're not finding Dyson spheres, you're probably going to find something interesting along the way.
Huston said, yet black holes provide distinct challenges to alien mega-engineers. The gravitational monsters tend to be less stable than stars in terms of their energy production. Whereas sunshine glows continuously, black holes often have bursts of activity followed by periods of quiet as they consume larger and smaller amounts of matter in their disks. An alien species might have to watch out for particularly large bursts that could destroy orbiting structures. But if a species is looking for something more powerful than a star, this could be it.