Hunting for Alien Megastructures

It’s a big galaxy out there. Even the most skeptical scientist has to accept that if a civilisation like our own exists, then there’s a good chance we’re not the only one to have ever done so. When most people think about SETI (the search for extraterrestrial intellgence), they imagine someone like Ellie Arroway searching the skies for radio transmissions. But what about looking in other ways? Perhaps a highly advanced alien civilisation might build structures large enough for us to see.

Vast structures, constructed on astronomical scales by advanced civilisations, is what the field of astroengineering is all about. This, admittedly, sounds audacious – and for the human race right now, it is. For us, astroengineering is still very much the realm of thought experiments, theoretical calculations, and science fiction. So it may be surprising to know that certain astronomers have made some quite serious attempts to look for astroengineered artifacts around other stars. With telescopes becoming ever more sensitive, and images being taken of exoplanets, the idea is starting to captivate imaginations once more.

Artists impression of a Dyson sphere, composed of a swarm of smaller satellites. Credit: Vedexent/Wikimedia Commons

In 1960, Freeman Dyson published a paper entitled Search for Artificial Stellar Sources of Infrared Radiation. His suggestion was that any megastructure constructed around a star should show itself by emitting more infrared light than it should. The solution was, simply, to look for any sources of infrared which appeared artificial.

Dyson put forward the ideas that any potentially advanced civilisation may need a tremendous amount of power to sustain itself. A method he proposed was to build a vast array of satellites which would enclose an entire star to harvest its energy – a concept which later came to be known as a Dyson sphere. While the concept wasn’t taken too seriously by Dyson himself, it was a powerful enough notion that it garnered a lot of attention.

Unfortunately, it isn’t as simple as looking for infrared light. Many stars, our own included, are surrounded by a disk of dust, and that dust emits plenty of infrared. To find a Dyson sphere, you need to look for a specific signature of infrared light, emitted at just the right set of wavelengths.

And that’s just what an ongoing project, headed by Dick Carrigan at Fermilab, has been doing. Astronomers regularly survey the sky to see what they might find, and Carrigan has been hunting through infrared data to search for Dyson spheres. To date, the project has a handful of candidates, but nothing definitive. Not yet.

But infrared isn’t the only way to spot Dyson spheres. In 2012 Geoff Marcy, an exoplanet researcher, was given a grant to hunt for evidence of Dyson spheres in data recorded by Kepler. In principle, any large artificial objects in orbit around other stars should be detectable in exactly the same way exoplanets are.

Artificial Worlds

Estimated sizes of the two Death Stars, compared with Earth and the Moon.
Credit: Invader Xan /

Astroengineering is, quite obviously, no easy feat; the larger the artefact being engineered, the more difficult it would be to create. For example, consider the infamous Death Star from the Star Wars movies. No official size was given in the original movie, but it’s been estimated to have been a few hundred kilometres in diameter (depending on who you’re asking), meaning that none of the engineering materials currently used here on Earth are strong enough to survive the kind of stresses involved in actually constructing one. In other words, White House petition or not, any attempt we were to make at constructing a Death Star sized object would crumple and break apart long before it was completed.

While the Death Star may be iconic in many of our minds as a vast artificial structure, it’s actually fairly small by astroengineering standards. Even the most grandiose estimates of how large it was are still small even compared to Earth’s moon, meaning something this size would be still be difficult to spot with a telescope. If we were to be able to actually spot an astroengineered structure, it would need to be far grander.

Similar to Dyson spheres are ringworlds, like those depicted in the Halo video games. A ringworld would consist of a giant ring in orbit around a star, constructed comfortably inside the star’s habitable zone. This would give an advanced civilisation a habitat with an area several million times the size of Earth in which to live. While a planet like our own could suffer as it begins to strain under the weight of an increasing population, an advanced society could have a population of trillions living on a ringworld.

Thinking on scales any larger, and things begin to become speculative, and some radical ideas have been put forward. For instance, a matrioshka brain would use a series of concentric Dyson spheres to harvest a star’s entire energy output to power a vast computer. Equally mind-bending is the idea of the Shkadov thruster which would use a gigantic mirror as a sail, enabling an entire star to be accelerated and moved, together with anything which happened to be orbiting it. But let’s not get ahead of ourselves.

One thing is quite certain – For any alien race to even consider an astroengineering project, they’d need to be dramatically more advanced than we are. Of course, as some scientists have pointed out, “There is no obvious reason why our own astronomical epoch favours the emergence of civilizations”. In other words, our galaxy is billions of years old, and there’s no reason to believe that advanced alien societies haven’t already been in existence for a long time before we humans had even evolved.

Could Dyson spheres and other astroengineered megastructures really exist elsewhere in the galaxy? Currently, we have no way of knowing. But the possibility alone is exciting enough to make it worth continuing to look. Perhaps if we find the right star to look at, we might just find something amazing.


27 Replies to “Hunting for Alien Megastructures”

  1. As well as an eager, aspiring wannabe Polymath, I have to admit, I’m a great lover of fantasy as well. The Death Star – the Halo Ring, Space-Stations that surround entire planets and interstellar travel… All of it is utterly fascinating to me.
    So needless to say, I’ve also had a look into the possibility of superstructures located outside a worlds gravity. In my eyes, the biggest problem would be the materials used – as, even if it’s via cryogenic means, unless we destroy ourselves first (It’s depressing to think so, but, personally, I think it’s the more likely future that awaits us) humanity will leave Earth.

    But I’d also like to think it’s possible to build star-sized supersturcturs through using Artificial Gravity. Although the amount of gravitational variations throughout the structure would be continuously changing to prevent the sub-structure being destroyed by the pulling and pushing of so much mass, maybe, just maybe, it could be done!

    That said, we need artificial gravity generators first, and a few barren moons/worlds to harvest the materials from.

    Either way, no matter what happens, I doubt we’ll build anything quite so large for quite a while yet 🙂

    1. I have a feeling, and I could be wrong, but don’t be surprised when in 10 years we are building these projects. As I hear from my buddies in technology, things are about to get CRAZY!!! So we might be on these ships : )

      1. I hope so too 🙂

        That said, they also said back in the 70’s that we’d have flying cars by the 90’s 😛

        Well, then again, we DO ACTUALLY have flying cars these days, completely safe too. Just not the means to manufacture them for mass-production, nor the people skilled enough to use them.

        That said, I eagerly await the day things like this become a reality!

      2. Our flying cars are ugly and they suck. Also they don’t have anti-gravity.

      3. Things are always claimed to get “crazy” in technology, even before the futurist idea got started, I would say since the 19th century or so. I wouldn’t read too much into it.

      4. Oh really?

        Here’s some food for thought, and this is directly from Neil Degrasse Tyson and Michiu Kiaku.

        1. We just cured AIDS, the vaccine will be available to the public by 2016.
        2. We now can regrow hearts, teeth, and other vital organs using stem cells harvested from the hosts own body.
        3. Star Trek-esque “tri-coder” devices designed to scan the human body and replace modern medical doctors are less than 10 years away.
        4. We are on the verge or at the very least, closer than we have ever been to achieving interplanetary travel, which will be followed closely by industry, and terraform efforts.

        5. We are on the verge of understanding matter in a way that we have never had before, discoveries in QM / ST will pave the way to this future faster than you even realize.

      5. Michio Kaku is not exactly a source I would put much trust in. Which of those predictions are Kaku’s (I’d wager #3-5, but am willing to entertain the possibility that I’m wrong), and which are Tyson’s?

  2. If such a structures would exist, then it wouldn’t be out of necessity but because of some alien culture that just builds it for the heck of it to show off. Just like artificial islands in Dubai.

  3. It bears noting that it has been proven that a circumstellar ring’s orbit would be inherently unstable, i.e. unless you actively keep it in position, it will move off-center until one side crashes into the central star. This fact was pointed out to Larry Niven, who then incorporated it into the later Ringworld novels.

  4. Go to YouTube and search for “ufo tether incident”. Watch the video(s). You will see some amazing stuff.

    1. Nothing exciting there. That is debris. It is out of focus due to
      depth-of-field, which is how pointlike particles get distorted into
      disclike images. At 3:01 you can clearly see the camera focus getting
      shifted back and forth. Satellite is in focus while debris is not, then
      vice versa. Any photographer or videographer is very familiar with this phenomenon.

  5. I don’t think you are correct about the “Death Star” crumbling. A 300 km high building on Earth would, indeed, crumble. A 300 km building (ship) in orbit would have an mass of maybe 10^20 kg and a gravitational acceleration of maybe 0.1 m/sec**2 (0.01 g), or less. That would mean (very roughly) that it would be comparable to a 1.5km building here on Earth – tough, but not impossible. Cut down on the mass or density a little, and it would be comparable to buildings extant on the Earth right now.

    Now, why you would build such a thing, and what you would use it for, are left as an exercise for the reader (or Emperor).

  6. It’s in the best interest for advanced civilizations to build mega structures in space. Planets are dangerous places (asteroids, climate, gamma rays, natural disasters…).

    1. Mega structures share all the same risks except climate (maybe you want to say “unnatural” disasters then 🙂 ), and the largest structures would include climate too.

      1. Indeed. But a civilization advanced enough to build gigantic orbitals would have the technology necessary to shoot down asteroids, to shield themselves from gamma-ray bursts, to control climate, etc.. They would design their dream worlds as opposed to be limited to a small and cramped rocky planet. 🙂

  7. If the concept of DNA’s inherit ‘manifest destiny’ is universal, and DNA (or its like) is the basis for life in the galaxy, then why would an advanced society elect to spend the time, mainly, and resources, secondly, to saturate a single solar system with themselves? To build such a multi-generational structure would only serve to maintain the species in the existing solar system. When, it would seem, species like humans and most every other form of life on Earth, seek to spread out to the maximum extents of an environment.

    The Polynesians didn’t build floating cities around their island to support more people. They struck out into the unknown to explore and unconsciously spread their DNA. Would there ever be a successful strain of life that was content to just sit around home rather than spread itself where ever and how ever it could? Such a theory seems to be a contradiction in the basic tenets of life.

    Choose one:

    A: spend all of our time, all of the next 10 generation’s time and all of our resources and build a synthetic place to live right here where we are.

    B: spend all of our time, all of the next 10 generation’s time and most of our resources to build starships to send out to other solar systems in the galaxy.

  8. I’m pretty sure any “advanced civilization” would figure out how to limit its own growth, obviating the need to consume materials or build things on an astronomic scale. Unless, of course, it’s an advanced yet stupid civilization, like ours.

    1. You forget that the members of any such civilization would be practically immortal. Plus if you can build a ringworld that can house trillions, you wouldn’t have to worry about population control.

  9. The rings in Halo are not like Ringworlds. They are much smaller, have no star at the center, and orbit a star much like a planet does.

  10. This seems to confuse creationist type teleology with causal processes.

    There is no concept of DNA’s having inherited some sort of ‘manifest destiny’ what I know of. It is a hereditary material that (sometimes and more recently, see the RNA world and RNA viruses) is used as genetic material in organisms partaking of the evolutionary process.

    “Destiny” is manifest [sic!] teleology of course.

    Similarly the tendency of populations of such organisms to spread in an environment, either as local invader or as more adapted, are apparent results of ongoing evolution that depends on original conditions. We have many examples of organisms going extinct locally or globally, actually many more than those who currently spread: 99.9 % of species have “unspread”.

    The question of “nurture vs nature” is a difficult one. While biology (“nature”) is perhaps most dominant in societal behavior, the moral default is to say that “naturalistic” ideology is a fallacy, meaning what freedom we have in choosing cultural behavior is free. But there is no “tenet” of having to spread (see above), we have many examples of seeming static traits and populations (long lived trilobites, lung fishes et cetera).

    1. My use of the phrase “manifest destiny” was more akin to the innate desire of humanity to spread and not some sort of teleological final product. This innate desire, as a theory, being a core component of the make up of DNA (or RNA as the case may be).

      So, “if” there is a natural, inbred tendency for any species to spread itself into every possible available environment; and, “if” this tendency is universal; then why would a species elect to stay at home rather than follow its breeding and seed the galaxy? (Better?)

  11. The constraint that technically advanced civilizations “destroy themselves” or need to “limit growth” doesn’t seem realistic. As technology increases the potential to prolong their originating culture increases, which we can see today.

    The local droughts that seem to have been important civilization killers earlier wouldn’t destroy our global civilization. Goes towards natural threats.

    We have both detected and started to act against the greenhouse gas increase (carbon dioxide, methane) that pre-industrial society started. Goes towards pre-industrial threats.

    Finally we have both detected and removed the ozone hole threat of PFCs that industrial society started. Goes towards post-industrial threats.

    I don’t know if anyone has integrated all of this. But naively I would think technological civilizations are more robust (more population, more resources, more technology and above all more observations).

    “Growth” is another word for “more efficiency” under some constraints (stagnated population), and “growth” is also another word for what market economy does. So I would expect that one would see growth over time no matter what type of society you would have, as long as it isn’t stagnated (dying).

    It isn’t “stupid” and it isn’t even very intelligent as it seems to be a given rather.

    Population control on the other hand is dependent on the population in question. Our own species seems to, given our terrestrial environment, self limit at a maximum of ~ 10 billions regardless of technology and given a loose set of successful societies. (In Rosling’s sense of democracies with market economy and social medicine.)

    The problem will rather become in the nex century how to maintain population at some viable 1 billion, since populations in successful societies tend to produce less than replacement levels of children as optimum for balancing their lives.

    Maybe creches and (perhaps) artificial wombs is one solution. I’m not so sure long life would be another, but just maybe such individuals would set a prize on repeating previous experiences out of a possible tendency for boredom.

    I don’t think these megastructures are likely. They serve no useful purpose that couldn’t be satisfied much more cheaply. If a system is too exploited you would most likely chose to migrate as it is much cheaper (Oort cloud utilization and later migration – no “stellar distances”, no “large structures”).

  12. Good solid Earth with its protective atmosphere will far surpass anything constructed in space. It is brute force against brute force out their.

  13. Out of focus debris does not accelerate/decelerate the way these objects did.

  14. MIT Prof. Gerard K. O’Neill in 1969 presented results from undergraduate projects in earlier years on space colonization near one of the Lagrange regions of Earth-Moon system L-4 or L-5. He published in 1974 Physics Today a summary. This study is also briefed in an interview of O’Neill that John D. Kraus for Cosmic Search magazine, which published 13 issues in late 1970s, all the issues being available online. I can provide specific references, but a google search also will fetch them.

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