Imagine a distant future, where we humans reach beyond the Earth, where we build civilizations on planets thousands of light-years away. Imagine a future of trade and transport between various planets and people living in them. While this is such a big dream, there are a few questions to consider: How would we communicate? What would a galactic government look like? How would we gather the amount of energy it would take to the power that civilization and the structures within it? What would it take for us to take that leap?
Nikolai Kardashev, an Soviet and Russian astrophysicist, developed the Kardashev scale in 1964. This scale could measure a civilization’s level of technological advancement based on the amount of energy they are able to use. According to that scale, in the 1st Evolutionary Stage, (which we’re currently in) plant-based fuel sources like fossil fuels, solar panels, and nuclear power plants are probably enough to settle other planets inside our solar system but not more than that. In the 3rd and final evolutionary stage, the energy requirement would be 100 billion times more than the full 385 Yottajoules our sun releases every second for expansion on a galactic scale. There is only one energy source that could suffice: a supermassive black hole.
It’s not intuitive to think of a black hole as a source of energy but because of their accretion disks (flat circular structures formed by diffused material orbiting around it), they become a massive energy source. Because of the conservation of angular momentum, particles there don’t just enter straight into the black hole, instead, they slowly spiral. Due to the high intensity of the gravitational field of the black hole, these particles convert their potential energy into kinetic energy as they inch closer to the black hole.
This kinetic energy is then radiated out into space because of particle interactions. The rate of matter to energy efficiency is astonishingly high: 6% for non-rotating black holes and up to 32% for rotating black holes. This outshines nuclear fission which is currently the most efficient and widely available mechanism to extract energy from the mass. Fission converts only 0.08% of a uranium atom into energy.
Freeman Dyson, an American mathematician, proposed the concept of the Dyson sphere in 1960 titled “Search for Artificial Stellar Sources of Infrared Radiation”. In that, he proposed that an advanced planetary civilization could engineer an artificial sphere around their main star, capturing all of its radiated energy to satisfy their needs. A similar but complicated design could be applied to black holes.
We would not want to cover a black hole fully with a sphere because, in order to produce energy, black holes need to be continuously fed. Also, the plasma jets shot by poles of many supermassive black holes would blow away any structure coming in their way. So, we might design something similar to a Dyson ring which is made of massive, remotely controlled collectors. They would swarm in an orbit around a black hole, perhaps on the plane of the accretion disk, but farther out.
These devices could use mirror-like panels to transmit the collected energy to a powerplant for a battery for storage. But we would need to ensure that these collectors are built at a precise radius (too close and they would melt because of the radiated energy, too far and they won’t be able to collect enough energy to survive). We would need several piles of earth worth of highly reflective material, like hematite, to construct the full system. In addition, we would also require a few more dismantled planets to make a legion of construction robots. Once built, the Dyson ring would be a technological masterpiece powering civilizations spread across the galaxy.
This all may seem like wild speculation, but even now, in our current energy crisis, we are confronted by the limited resources of our planet. There may already be a civilization out there that we don’t know about. Only time and our scientific ingenuity and advancement will tell.