Moon's mini-black hole illumination of planet as technological signature
08/05/2024, Avi Loeb, avi-loeb.medium.com
Are you worried about high energy bills and excess waste?
Imagine a magical wastebasket that turns any garbage you throw into it into pure energy with a mass-to-energy conversion efficiency of 10% – ten times higher than the most efficient nuclear fuel. Once the garbage enters this magical bin, it disappears – never to be seen again. Sound like science fiction? It's not. Nature has given all these qualities to black holes. Once the garbage falls beyond the event horizon, it becomes invisible to the outside world.
Advanced civilizations could meet their energy needs by passing their debris through an accretion disk around a miniature black hole that orbits like a moon around their planet.
The technological challenge of creating a mini black hole is the enormous mass density required to create it. If it were possible to create a mini black hole and keep it as a glowing moon, this artificial furnace could replace the Sun in lighting and heating a rogue planet that would otherwise be frozen and uninhabitable.
Cosmologists speculate that mini black holes could have been created in the early universe when radiation density was high enough. However, a sufficiently advanced technological civilization could have created a mini black hole to meet its energy needs.
Stephen Hawking realized in 1974, that a mini black hole would glow on its own, even without an external fuel source. So-called Hawking radiation is brighter for smaller black holes, causing them to evaporate in a finite amount of time. What would be the optimal mass of a black hole to power an Earth-sized planet for a year?
Imagine a mini black hole in low Earth orbit at an altitude of 1,500 kilometers, about a quarter of the Earth's radius. Such a black hole could provide the energy flow that Earth currently receives from the Sun if its luminosity (energy emitted per unit time) were ten billion times smaller than the Sun's luminosity.
For a planet like Earth, the source would illuminate the surface below it, alternating day and night every ~90 minutes. The length of the artificial day would scale with the source's orbital radius to the power of 1.5.
The required energy flow could be provided by a mini black hole with a mass of one hundred thousand tonswhich is thirty times the mass of Starship and equivalent to the mass of an asteroid 60 meters in diameter. The Hawking evaporation time for such a black hole is on the order of a year. To keep such a furnace going for longer, it would need to be fed with debris every year. This act would be like putting logs in a wood-burning fireplace. A civilization could automate this process by continually injecting material from another moon of similar mass orbiting the black hole and feeding its accretion disk to keep it stable and compensate for the losses from Hawking radiation.
The Hawking radiation from such a mini-black hole would include high-energy particles with a rest mass one hundred times that of a proton. These particles would be processed by the planet's atmosphere into heat and optical light that could fuel life on the planet's surface.
The technology to create a mini-black hole of this mass would require a mass density 61 orders of magnitude greater than that of water, or 44 orders of magnitude greater than that of an atomic nucleus. Whether such a technological feat has been accomplished by any advanced civilization in the Milky Way galaxy remains to be seen. Gamma-ray telescopes can look for moons (mini-black holes) as a technological signature around exoplanets.
If we ever find a rogue rocky planet without a stellar-mass companion illuminated by a bright gamma-ray moon, we'll have to consider the possibility that the source was created or trapped by an advanced technological civilization. I was presented with the 2024 Space Anomaly Hunters Award last night in Miami, Florida, but I'd be much more excited if I discovered an anomalously bright moon.
There is no better indicator of technological innovation than creating a furnace out of a space-time warp in the shape of a miniature black hole.
There are currently a large number of startups aiming to create compact thermonuclear reactors. A mini black hole would be much more efficient and environmentally friendly.
Scientific article: Illumination of a planet by a black-hole moon as a technological signature
Translation: Alexander Tarlakovsky (blog tay-ceti)
Original: Illumination of a Planet by a Mini-Black-Hole Moon as a Technological Signature
