Categories: Guide to Space

What Are Alien Megastructures?

Did scientists find a giant alien structure around KIC 8462852? Probably not, but if they did, what would these structures look like?

In the summer of 2015, astronomers announced a strange new discovery from NASA’s planet hunting Kepler space observatory. Some object was blocking out about 22% of the light from its parent star: KIC 8462852. Even the largest planet in the Solar System, Jupiter, would only block out 1% of a star’s light, so something much larger must be doing this. But what?

Astronomers proposed a few ideas: a cloud of comets, or a maybe the debris from a recently destroyed planet. But another idea was put on the table: an alien megastructure.

Detailed map showing stars to around magnitude 12 with the KIC 8462852 identified. It’s located only a short distance northeast of the open cluster NGC 6886 in Cygnus. North is up. Source: Chris Marriott’s SkyMap

Now keep in mind, aliens are way down in the list of possibilities here. It’s almost certainly, for sure, probably not aliens. Seriously, every other possibility is a zillion times more likely than aliens. But there’s a remote, non-zero chance that it’s aliens, and their alien megastructures.

Are you having trouble imagining what an alien megastructure might look like, and why it would exist? No problem, join the club. All we’re doing is extrapolating from our current demand and growth for energy to its logical conclusion.

Imagine the future of humanity. We use more energy now than we did in the past. And in the future, we’ll want even more energy. Eventually we’ll use up all the energy on Earth, then we’ll figure out how to use up all the energy flowing out of the Sun. After that, we’ll use up all the energy in the entire Milky Way. Finally, we’ll use up all the energy within every single galaxy that we can get our hands on.

Dyson Sphere. Credit: Eburacum45

And to do this, we’re going to want to build megastructures. Aliens will call them alien megastructures. So what kind of megastructures will we build to extract all the energy from the Sun?

Imagine you encased the entire Sun in a rigid sphere; this the concept of a Dyson Sphere, first described by Freeman Dyson back in the 1960s. In fact, if you dismantled every single planet, moon, comet and asteroid in the Solar System, you could build a shell around the Sun about half a meter thick. It would have an interior living space of about 600 million times what we currently have on Earth. And if you set the whole sphere turning, the people at the equator would experience Earthlike gravity from the centripetal force pushing them outward.

This actually isn’t a great idea. You’d have to be pretty close to the equator to experience any gravity, and the forces on the whole sphere would try to tear it apart. There are no materials that we could imagine that could hold a structure like that together.

There are Dyson rings and spheres and this, an illustration of a Dyson swarm. Could this or a variation of it be what we’re detecting around KIC? Not likely, but a fun thought experiment. Credit: Vedexent

A more realistic concept is a Dyson Swarm, where you build a single solar power collection satellite. And then use its energy to manufacture more of these things until there’s a cloud of them orbiting the Sun, and you’ve got your greedy hands on every single stray photon.

Seen from afar, a cloud of these satellites would block the light from the Sun as they swept past, and make astronomers wonder if they’re seeing an alien megastructure. But for a powerful alien civilization with the ability to dismantle a Solar System, this is just the first step.

The next megastructure is a Shkadov Thruster. This is a reflective half shell that’s put in place beside a star. Light pressure from the star pushes outward, holding the shell in place, and gravity from the shell pulls the star towards it. Over billions of years, a civilization could reorganize all the stars in their galaxy into a more useful configuration. Any galaxy that isn’t already moving away faster than the speed of light could be raw materials for a powerful civilization looking to get at every joule of energy.

This all sounds like amazing science fiction, but the reality is that we have the tools to see if these alien megastructures have been constructed across the Universe. Although a Dyson sphere would block out the light from a star, infrared radiation would still escape from the outside of the shell.

Star KIC 8462852 in infrared (2MASS survey) and ultraviolet (GALEX). Credit: Infrared: IPAC/NASA / Ultraviolet: STScI (NASA)

Astronomers have performed surveys to look for unusual objects that shine brightly in the infrared, and nothing has turned up. They’ve even looked at thousands of galaxies, to see if any have been completely colonized and converted into Dyson spheres. Still nothing, but they’ll keep looking.

In just the last few months, the study of KIC 8462852 has gotten stranger. Astronomers looked back at old images of the star and found that it’s been slowly dimming over the last century. And this rules out the idea that a cloud of comets is blocking the light from the star. It’s still probably not aliens, but it’s definitely not comets.

Although the idea of a megastructure sounds like science fiction, there’s nothing in the laws of physics that prohibits it. It would just take engineering at a scale that boggles the imagination. Fortunately, we should be able to detect any aliens building their megastructures in our neighborhood, so we’ll be able to admire their handiwork from afar. As always, let’s hope they’re friendly.

So what do you think is causing KIC 846852 to dim? Which theory do you like the best? Tell us your thoughts in the comments below.

Fraser Cain

Fraser Cain is the publisher of Universe Today. He's also the co-host of Astronomy Cast with Dr. Pamela Gay.

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