Just when you thought theoretical astrophysics could not get any more interesting, Harvard’s Avi Loeb comes along with a proposal that sounds straight out of a sci-fi novel. In his latest research paper, “Illumination of a Planet by a Black Hole Moon as a Technological Signature,” Loeb suggests that advanced civilizations could harness energy from a “Black Hole Moon” orbiting their home planet. Since we are having fun, in this article we will see how Avi Loeb’s vision might become a perpetual solution to our planet’s trash and energy problems. Here’s a clue: It’s not going to happen in our lifetimes without help from aliens who give us both the mini black hole and installed self-repairing space elevators to transport our trash up to waiting self-reparing robots who process it and give us the energy back on the ground level on earth in exchange.
The Concept: A Cosmic Pet That Needs Feeding
Loeb’s proposal involves creating a small black hole, weighing just 100,000 tons, and placing it in low earth orbit around a planet. (This reminds me of Steve Martin’s quip on how to be a billionaire and not pay taxes, “First, get a billion dollars.”) This cosmic oddity would naturally evaporate in about 18 months due to Hawking radiation. But here’s the kicker: by feeding it a mere 2.2 kg of matter per second, we could maintain this black hole while reaping[1], an astounding 40 quadrillion watts of power. It’s like having a pet that produces unlimited energy – as long as you remember to feed it regularly.
For some perspective here, the blue whale, the largest animal on Earth, can weigh up to approximately 200,000 kg. Therefore, our black hole of 108 kg would have a mass equivalent to about 500 blue whales. The figure 2.2 kg of mass per second is 190,080 kg per day, so we’d “only” have to feed it the mass equivalent of about 1 blue whale daily.
Energy Potential by Constant Mass to Energy Conversion
Matt Williams writing for Universe Today wrote that Loeb’s proposed 1011g black hole could continuously supply 40 quadrillion (4015) Watts, if fed enough mass continually. Does that check out?
Mini black holes are theoretical objects that could exist with masses significantly lower than stellar black holes. Such a black hole could theoretically orbit Earth without posing a significant threat, as indicated by studies suggesting that mini black holes can pass through Earth without consuming it rapidly[2][4]. The energy output from a black hole being fed mass can be considerable. For example, if the black hole absorbs matter, it can emit energy equivalent to the mass-energy of that matter according to E=mc2. The radiation emitted will primarily be in the form of high-energy photons, which can include gamma rays, but also other particles. The exact spectrum of emitted radiation depends on the mass and the surrounding environment of the black hole.
As the black hole evaporates, it emits photons across a range of energies. This can encompass the entire electromagnetic spectrum but is particularly concentrated in the high-energy range due to the black hole’s temperature. The peak energy of the emitted photons from a 1011g (108 kg) black hole can be estimated using Wien’s displacement law, indicating that a significant portion of the emission would be in the gamma-ray region due to the high temperature. Other factors would influence the energy output spectrum.
- Accretion Dynamics: If the black hole is actively accreting matter, the interactions between the infalling matter and the black hole can lead to additional emissions, potentially altering the spectrum.
- Surrounding Environment: The presence of other matter and radiation can influence the emitted spectrum through processes like Compton scattering.
The assertion that a black hole of this mass could provide such energy levels is theoretically plausible, given the right conditions for mass accretion and energy conversion.
Practical Implications
- Physical Size: In practical terms, a black hole of this size would be nearly impossible to detect directly. Its event horizon—the boundary beyond which nothing can escape—is so minuscule that it would have a negligible gravitational influence on the surrounding space at any observable scale. Imagine it as an invisible “suck hole” fixed in space, similar to a point in a geostationary orbit around our planet, where it would remain indefinitely without any decay in its orbit.
- Surrounding Environment: If such a black hole were to exist near Earth, its gravitational effects would be negligible unless you were extremely close to it. For instance, the gravitational pull of the Earth is felt at a much larger scale, and the black hole’s influence would only be significant at distances comparable to its event horizon.
- Energy Harvesting: The concept of harvesting energy from Hawking radiation emitted by such a small black hole is theoretically intriguing but practically challenging. The amount of energy emitted would be extremely low, given the small size of the black hole, and capturing that energy effectively would require advanced technology and materials.
Energy Harvest by Radiolysis
In orbit, a micro black hole emits detectable Hawking radiation, releasing energy (we think) primarily in the form of gamma rays as it evaporates. When water is exposed to these gamma rays, high-energy photons interact with water molecules, leading to the formation of free radicals through a process known as radiolysis. These free radicals can decompose water (H₂O) into hydrogen (H₂) and oxygen (O₂).
The efficiency of hydrogen production can be significantly enhanced by using specific materials such as aluminum oxide (Al₂O₃) or semiconductor catalysts. Experiments indicate that introducing Al₂O₃ particles into water can increase hydrogen yield by over two orders of magnitude compared to water alone. Additionally, catalysts like platinum group metals (e.g., ruthenium, rhodium, palladium) on semiconductor materials can further improve hydrogen generation efficiency.
For a black hole with a mass of 100,000 tons (approximately 1011 grams or 108 kg), the Schwarzschild radius would be 1.48 x 10-27 meters. This is smaller than a single hydrogen atom! A spherical aquarium with a radius of about 10 meters could effectively harvest gamma rays from the Hawking radiation emitted by such a black hole. This size would ensure sufficient water to attenuate gamma radiation while maximizing the surface area for energy harvesting. The harvesting shell would also need to accommodate a portal for space robots to add trash mass as fuel.
The gamma rays emitted by the black hole could excite electrons within a catalyst, facilitating the formation of hydrogen gas and simultaneously producing oxygen from water. Envision a spherical aquarium of water surrounding the black hole, significantly smaller than our Moon. The hydrogen generated could then be transported back to Earth for use in fuel cells, generating electricity.
Escape Velocity
To maintain a stable orbit around Earth and avoid being pulled in by its gravity, an object must travel at a specific orbital speed. The black hole with a mass of 1011 grams would need to travel at approximately 7,738 m/s (or about 27,800 km/h) to maintain a stable orbit around Earth at an altitude of about 300 km. This speed is similar to the orbital speeds of satellites in low Earth orbit.
The Reality Check: Challenges and Possibilities
Before we get too excited, let’s consider the practicalities. Creating a black hole of this size requires compressing matter to a density 60 orders of magnitude above that of solid iron. The technology needed for this feat is so far beyond our current capabilities that it might as well be magic.
But let’s assume we somehow overcome this hurdle. The next challenge is feeding our cosmic pet. Supplying 2.2 kg of matter per second might not sound like much, but it adds up to about 190 metric tons per day. To put this in perspective, the largest payload ever launched into space was the Saturn V rocket, which could carry about 140 metric tons to low Earth orbit. We’d need to launch more than a Saturn V rocket’s worth of matter into space every single day just to keep our black hole fed.
The logistics of such an operation are mind-boggling. We’d need to revolutionize our space launch capabilities, perhaps developing space elevators or other advanced propulsion systems. Even then, the energy required to constantly lift this much mass out of Earth’s gravity well might offset a significant portion of the power we’d gain from the black hole.
A Cosmic Gift from Beyond: The All-Inclusive Package
Now, here’s where things get even more speculative – and convenient. Imagine that an advanced alien civilization decides to solve not just our energy problems, but also our waste management issues in one fell swoop. They gift us not only the pre-made black hole but also a complete infrastructure to feed it and harness its power.
Picture this: 15 self-repairing space elevators strategically placed around the globe, each equipped with advanced feeder robots. All we humans need to do is drive our trash to one of these 15 locations each day. The alien system would handle everything else – sorting, processing, and feeding the black hole at the optimal rate. It even comes with a built-in safeguard: the system stores excess matter, ensuring we can never overfeed our cosmic pet.
But wait, there’s more! At each of these feeder stations, we could draw the energy produced by the black hole in the form of hydrogen gas or electricity. It’s like having a cosmic vending machine that turns our garbage into clean, unlimited energy.
Sounds too good to be true? That’s because it probably is. While this scenario solves many of the logistical issues, it raises a whole new set of questions. Why would aliens go to such lengths to solve our energy and waste problems? What’s in it for them? And how would we ensure this gift doesn’t become a Trojan horse?
Remote Detection Skepticism
With all of this in place, wouldn’t the spherical aquarium, aqua ball dynamo (Aquamo?), absorb all of the Hawking radiation if well constructed? What’s left for us to see? In other words, Loeb’s idea of using these as cosmic technology detectors seems to rely upon there being some wasteful generators out there. This is not entirely improbable, but questionable. Sufficently advanced aliens might not waste energy by letting it leak into the cosmos.
The Bottom Line
Whether we create it ourselves or receive it as an all-inclusive cosmic gift package, the idea of a “Black Hole Moon” providing unlimited power is certainly intriguing. However, we’re still firmly in the realm of speculative science – or perhaps science fiction. The technological hurdles are immense, and the implications of such a system are far-reaching and potentially problematic.
For now, I’ll keep advocating for more grounded approaches to solving our energy and waste management challenges. But I must admit, the idea of turning our trash into limitless clean energy via a black hole is an entertaining thought experiment. It reminds us that in the face of seemingly insurmountable problems, human imagination – and perhaps a little alien intervention – knows no bounds. Just don’t expect me to start looking for space elevators on the horizon anytime soon.
Read More
[1] https://iopscience.iop.org/article/10.3847/2515-5172/ad6e7a
[2] https://phys.org/news/2011-05-mini-black-holes-atoms-earth.html
[3] https://www.livescience.com/53627-hawking-proposes-mini-black-hole-power-source.html
[4] https://www.nationalgeographic.com/science/article/110526-mini-black-holes-pass-through-earth-lhc-space-science
[5] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9185291/
[6] https://en.wikipedia.org/wiki/Radiolysis
[7] https://sess.stanford.edu/research/energy-harvesting
[8] https://www.sciencedirect.com/topics/biochemistry-genetics-and-molecular-biology/radiolysis
[9] https://www.sciencedirect.com/science/article/abs/pii/S0969804319311108
[10] https://ieeexplore.ieee.org/document/9186841
[11] https://frib.msu.edu/news/2023/isotope-harvest
[12] https://www.pnas.org/doi/full/10.1073/pnas.1402036111