This week astronomers announced an unusual transit signal from another star. Although it’s most likely a natural phenomenon, one remote possibility is that this is some kind of alien megastructure. Freeman Dyson and others have considered this idea for decades. Today we’ll talk about the kinds of structures that aliens might want to build.
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Announcer: This episode of Astronomy Cast is brought to you by Swinburne Astronomy Online, the world’s longest running online astronomy degree program. Visit Astronomy.SWIN.edu.au for more information.
Fraser Cain: Astronomy Cast episode 388, Megastructures. Welcome to Astronomy Cast, our weekly facts-based journey through the cosmos where we help you understand not only what we know but how we know what we know. My name is Fraser Cain. I’m the publisher of Universe Today and with me is Dr. Pamela Gay, a professor at Southern Illinois University Edwardsville and the director of CosmoQuest. Hey Pamela, how you doing?
Pamela Gay: I’m doing well. How are you?
Fraser Cain: Good. It was so great to see you in person.
Pamela Gay: It was.
Fraser Cain: Yeah, so for those who don’t know, last week, as of when we’re recording this, Pamela and I were in person at OSU thanks to Paul Sutter from Ask A Spaceman podcast. He hosted us and put us to work doing – I did a seminar. We did a live show with astronauts and it was awesome. We had a great time.
And there is a missing hidden episode, episode 389, that we actually recorded with Paul Sutter. And that’s just gonna show up in your feed. There’s no video to go along with it. We just plunked the microphone down on the table and we did an episode, all about [inaudible] [00:01:27]. So hopefully that’s gonna be what’s gonna come up next week.
Pamela Gay: Yes, or intermediately. It’s likely to be an intermediate episode, a hidden episode [inaudible] –
Fraser Cain: A hidden episode, yeah, exactly, a bonus episode. Okay. Any other announcements?
Pamela Gay: For those of you who are watching this live, there is the White House Star Party today here in the United States and there are satellite events all across the United States. So check out what’s going on near you. There are people with telescopes looking to show you a little bit of the sky.
Fraser Cain: All right.
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Fraser Cain: This week astronomers announced an unusual transit signal from another star. Although it’s most likely a natural phenomenon, one remote possibility is that this is some kind of alien megastructure. Freeman Dyson and others have considered this idea for decades. Today we’ll talk about the kinds of structures that aliens might want to build.
Now, we were super fortunate when this news came out that we did the Weekly Space Hang Out on Friday. And Kimberly Cartier who is the second author on that paper is one of the regulars on the Weekly Space Hang Out. And so she was there to talk about it for 20 minutes and we asked a lot of questions. So if you wanna hear, like, literally from the source, check out the last episode of the Weekly Space Hang Out, the one that came out on October 16?
Pamela Gay: Yeah.
Fraser Cain: Yeah, but for those who too long didn’t listen, can you give the short synopsis about the news that came out this week?
Pamela Gay: Yes. It came out last week and it appears that there is a star in the coupler field that is in a non-periodic kind of way getting brighter and fainter. And the way it’s getting brighter and fainter looks like multiple objects passing in front of the star. They’ve done follow-up observations trying to figure out, is this sunspots, is this weird something natural about the star?
And so far all of the things that they’ve tried to match it to aren’t working out. And the best they can figure is there’s something physical, an object set of some sort that keeps passing in front of the star. And there are multiple of them doing this in a way that is really hard to model and doesn’t look like anything we’ve previously seen in nature. So if it’s a natural event it’s probably an extremely short-lived natural event.
Fraser Cain: So the kinds of natural events that we’re talking about would be things like a cloud of comets moving past the star. I mean, they’ve already ruled out that it’s planets on funky orbits. So the ideas are having to get pretty out there now.
Pamela Gay: Yeah, and this is where people end up – because we do know it’s a low probability event – end up jumping to the most wild of all the low probably events.
Fraser Cain: Right.
Pamela Gay: So one of the things, as you eluded to, was perhaps the star passed near another star recently and this triggered a whole onslaught of comets from that star system’s version of the orc cloud and these are all plunging in on mass. Kind of dramatic, kind of crazy. But the alternative hypothesis is, what if this is a bunch of manmade structures?
Fraser Cain: Alien-made, yeah. So normally we would be very skeptical, we’d be toning it down, we’d be telling you that the chances that it’s aliens is super remote. But today Fraser’s imagination is taking the driver’s seat and so we get to just go off into crazy places to think about this.
All right. So then why is this one of the theories that’s been posted is that this is somehow an artificial created megastructure by some alien civilization?
Pamela Gay: Well, so the probability that we’re looking at the aftermath of planets that collided and left behind big old pieces of shrapnel or that it is an incoming swarm of comets, these are all low probability things that live, if they happen, for a very short period of time. Comets self destruct, planets reassemble.
And at the same time the chance that a civilization that’s older than our own might have had time to start mining their asteroids into giant structures doesn’t seem like it’s necessarily that much more improbable. Now, the thing is, we have no idea what the frequency of life is, what the frequency of civilizations are.
So for all we know it is much, much more common for there to be megastructures out there than for there to be planets colliding. And we don’t know. And it’s that not knowing that makes it impossible for us to say, what is the more improbable explanation for what we’re seeing?
Fraser Cain: Okay. So let’s go back then and let’s talk about some of the kinds of structures that future civilizations might build, and then maybe how we would go about actually looking for these things? So we’re gonna stay completely in the laws of physics here, we’re gonna try anyway, and really talk about sort of what is the end state? What is the thing that the most sophisticated, most powerful, most – the aliens with the most mastery over their physical environment could do with the raw materials that they have at their disposal?
So let’s sort of start something that’s maybe closer to where we are today. What kinds of structures could, in the next few thousand years maybe, some kind of alien civilization put together?
Pamela Gay: Well, so the most obvious is your giant Star Trek class space station. Something out there that is comparable in length to the size of the moon. Think, not star but friendlier and maybe more tubular so that you can have all the spacecraft docked up nice and tight.
There’s the giant spinning ring philosophy, so depending on how you want to do it, you either build something that is perpendicular to the sun and spinning that is fairly small, perhaps the size of a planet. And because of that spinning it’s able to create artificial gravity. You put inner walls on that ring and it keeps its own atmosphere inside.
But if you are a sufficiently large civilization with sufficiently large heavy moving equipment, instead of just building a planet-sized spinning ring that is in orbit around a star why not build a ring around the star. And some people will then go as far as to say, well, that’s just too close to hold on to the star. And that’s where we get back to something we’ve seen in Star Trek, a Dyson sphere
Fraser Cain: Right. And Freeman Dyson sorta came up with this idea. Who knows if people had sort of imagined it beforehand, but the idea, right, is to try and capture all of the energy that comes from a star. Right now we only collect a tiny, tiny fraction of the energy that’s given off by the sun. It goes off into space, worthless, worthless space. We should be capturing that energy and then using it to fuel our plots and dreams. So what would sort of an actual Dyson sphere require?
Pamela Gay: An actual Dyson sphere is extraordinarily complicated to build because you’re dealing with, first of all, different amounts of gravity at different points inside the sphere. So you have a sphere rotating. We’ve all spun up a globe before. Now if you think about where you have to be moving the fastest in order to make it all the way around that axis, you end up with heavier gravity down in the Equatorial region than you have up towards the pole. This causes the atmosphere to lump up along the center.
And in order to get that full sphere going, well, first of all you have to figure out all of the physics of giant doors in and out because you figure you’re probably gonna wanna explore the rest of the universe occasionally. You’re gonna wanna look out occasionally. You have to figure out how do you distribute mass so that you’re not crumpling your structure? How do you deal with all of the weather that’s likely to form? It’s structurally kind of a nightmare because you do have this gradient and force being exerted on the ring, gradient and mass piling up across the ring.
And then there’s things like you’re probably gonna stick all of your light collectors that are obscuring your surface in those low gravity polar regions. And it just goes on and on in terms of nightmare after nightmare.
Fraser Cain: Right. Now, when you’re talking about sort of the low gravity regions, right, like say you actually enclose the whole star in a sphere and then you set that sphere turning to provide some kind of gravity, right, artificial gravity, it’s only gonna be felt, right, at the Equatorial sections. And then as you go further towards the North or South Pole you’re gonna have less and less gravity until if you were actually at the north or south end of this sphere –
Pamela Gay: — no gravity.
Fraser Cain: — there would be no gravity.
Pamela Gay: Yeah.
Fraser Cain: And you would sort of fall down and then you would [inaudible] [00:12:08] places where there would be higher gravity.
So because the – and I think someone did the math, right, that if you took the entire solar system, dismantled it, you could only get a sphere that’s about 20 centimeters thick.
Pamela Gay: And that’s not gonna do it for you.
Fraser Cain: Right. And so what is the physical stuff – you know, what material in the universe – if you could turn the entire solar system into the toughest material in the universe, could you build a rotating sphere the size of the earth’s orbit and have it hold together with these kinds of stresses and title forces and stuff? It just wouldn’t work.
Pamela Gay: No, no. And with the technologies that we know of today, you’d probably want to build it out of carpet and fiber. And we just don’t have enough stuff. And even if you put all of your stuff into building this sphere, you’re still gonna wanna have houses and cities and you’re gonna need to have agriculture. So you’re gonna have to have thick dirt in some places. And why are we going to kill all the whales? You probably wouldn’t have oceans.
And this is where reading in science fiction we find lots of alternate answers. This is where we find Larry Niven’s Ring World, which is one of my favorites.
Fraser Cain: Yeah.
Pamela Gay: Instead of building a sphere just build the part that matters, that Equatorial region.
Fraser Cain: Right. And I think in Niven’s book there was like a wall around the edge of the ring. Like imagine a ribbon that goes all the way around at the earth’s orbit and then it’s covered with walls on the edges of the ribbon. And then this thing turns. The atmosphere is kept in by these walls around it. The turning gives you that gravity and the thing should theoretically work.
But I think even in Ring World Niven admitted that the stresses – there’s no way you could keep the thing perfectly balanced. It would eventually tear itself apart.
Pamela Gay: Right, right. And so this is a matter of have we just not figured it out. And if you think about it, it took humanity a little while to figure out the beauty of the arch, to figure out how to build the bridges like the Golden Gate Bridge that had these beautiful arches of cables that support the bridges beneath them.
And technology continues to advance to the point that we now not only have the capacity to start building kilometer-high buildings but to the pioneers building everything out of brick and rock, that’s an impossible thing to conceive of. So who knows?
Fraser Cain: Yeah, but these concerns have absolutely been considered by – and even Dyson considered this. And so, one of the other ideas is to be able to call the Dyson swarm. Have you looked into this at all?
Pamela Gay: It’s not – I have to admit, I tend to go down more of the Babylon five [inaudible] [00:15:08] spitting cigar instead. But –
Fraser Cain: Well, you get both, right? So with the Dyson swarm you are still dismantling the solar system so [inaudible] solar system –
Pamela Gay: — as one does.
Fraser Cain: — as one would need to. But then what you do is you build essentially satellites, solar satellites that act like a big cloud around the sun. And so these are all on all different orbits but they overlap in such a way that you collect a big chunk of the energy that’s coming out from the sun. But there’s no requirement for this structure, right, because they’re not attached to each other. they’re just flying past and collecting the sunlight. And there’s always cover. So if the sunlight gets past the one cloud of satellites, it gets to the next one and they capture it, right.
And then for habitation, back to the spinning rings, so you could set up at various places big O’Neil cylinders with the open end pointed towards the sun and they’re just spinning. So you wouldn’t – nothing would be connected but you would maximize the habitableness of the solar system by just kinda dismantling everything and reorganizing it into a structure that really worked.
Pamela Gay: And I love the way you see dismantling our solar system into a bunch of solar panels and spinning rings as an improvement. Not sure I agree with you there but that’s okay. So the key where we get stuck is how do you take solar energy collected from all of these panels and distribute it to all of the societies that are now living in spinning rings, the Martian style except much bigger? And here you start to have perhaps more of what you see in Neal Stevenson’s Seven Eves where you have a whole collection of different sub societies, each in their own solar system, and figuring out this one lives on this panel, this other one lives on this other panel. And do you then end up with genetic drift from one base station to another?
Fraser Cain: Or they’re beaming energy at each other with lasers or whatever, right? There’s gonna be some kind of math that they figured out that it’s better to live at the – where the panels are or it’s better to beam it to another place.
So now this all just sounds like just future magic technology, and it is but what’s kind of interesting about it, and this is sort of where it comes back to the story that happened this week, is that these kinds of things could be observed, right.
Pamela Gay: And they could be observed and they could be a necessity. We look at our own solar system – or at least I look at our own solar system as a perfectly beautiful place that is currently not trying to kill me too bad. So let’s keep the planet earth going. But if you have read Neil Stevenson’s Seven Eves, and I don’t think is a spoiler, I’m pretty sure it’s on the back of the book, the planet earth becomes uninhabitable for a large chunk of time.
And because of that and because they’re given some prep time ahead of time, we become a space faring civilization just to save our own genetics. And it could be that other civilizations have already hit that horrible, oh, we need to be out among the stars now dilemma that leads to megastructures as the only way to keep going.
And now we’re looking for them as, well, earthbound ones are probably linking radio and space-bound ones are probably using encrypted point-to-point communications, as a good civilization should. But they’re not radiating normally.
Fraser Cain: So what do you mean not radiating? Like what would the signature be – if you looked at a star that was surrounded by some kind of megastructure, some kind of cloud, massive space station, what things would look different than when you look at a regular star?
Pamela Gay: So when we look at our own sun we see that it has this beautiful black body distribution of light that tends to peak in the green. And everything is nice and smooth. But if you’re surrounding that with more and more solar panels, the solar panels are going to be absorbing out high energy light, the visible colors, the ultraviolet colors. And all of the surfaces of your megastructures are going to be warm. And so they’re going to be giving off light in the infrared.
Now, planets do do this too but planets have orbits we kinda understand and megastructures, well, they’re going to have those same high infrared, I’m a warm thing radiation properties but they’re not going to do it in a way that looks like the way a planet does it.
Fraser Cain: And so using like maybe an infrared telescope and looking at these stars, you would see stars with a really strange energy signature, that it would be leaking a lot more infrared, a lot less visible light. And it would be a real telltale sign that there’s something very strange going on around that star.
Pamela Gay: Well, if you have a ring in particular it would look like two super imposed black body curves, one at the temperature of whatever the heck that ring is at, probably something resembling earth temperatures. And then the star would be trying to radiate a way in the temperature the star is at which is going to be much, much warmer. And if we had a binary system or a planet you’d see these two black bodies fading and getting brighter as one passes in front of the other. But if it’s a ring, it’s permanently superimposed and never changing in brightness. And that just doesn’t occur in nature.
Fraser Cain: And the other part as well is with Keplar it uses this transit method to spot objects moving in front of the parent star and try to figure out how long did it happen, how big is the planet, what’s its mass, things like that. But in fact, different shaped objects – like if you had a triangle pass in front of a star it would give off a different light curve than a circle or a square or some other kind of unusual shape.
Pamela Gay: Yes. And the way to think about this is if you have a spherical object that is moving in front of another object – I’m apparently going to eclipse my face for those of you watching online – it’s curved edge will cause a smooth decrease in the amount of light that is actually curved in how it’s decreasing. So there’s this – as the amount – it’s a geometric blocking
Now, if instead it is a triangle coming in, you’ll have a sharper edge. It all has to do with how you do the math. Sphere is gonna be a pi r squared triangle. It’s just different. It becomes a geometry nightmare, but we know how to do geometry.
Fraser Cain: Right. And I think one of the really interesting science that’s been done is astronomers have figured out they can look at things like – they can look at the light falling on a planet or looking at the light falling on its exo moon, like once they get powerful enough and then try to get a sense of how much illumination, if there’s cities on that planet, if you have like some kind of coriscant, corsant – I don’t know how you say it –
Pamela Gay: Corisant.
Fraser Cain: — corisant from Star Wars, right. you get a planet that’s an entire city. That would give off a different light signature than one that had oceans and darker colored mountains and things like that, ice.
Pamela Gay: And we’ve simulated this with our own moon. We’ve actually unfocused telescopes, looked at the moon, looked at the variations and light of the moon as the earth rotates to try and figure out, can we reproduce the distribution of light on the earth? And we can to a certain degree. It’s not a perfect science but it’s a starting point.
Fraser Cain: Now, one of the future sort of thought processes if you – like say you have some alien civilization and they convert one solar system into some kind of Dyson sphere, Dyson cloud, Dyson swarm that gives off that infrared signature, and then they move to another solar system and then they move to another one. And then they eventually theoretically, if there’s no reason to stop them, they would colonize and convert their entire galaxy into, I guess, whatever composition, whatever structure made the most sense to them.
And what I think is really super fascinating, again, astronomers have thought about this, that would give off an infrared signature but it would be a galaxy wide. And actually there was a recent survey done with NASA’s WISE telescope to look for – I think they studied 10,000 galaxies to see if any of them were a place where some future aliens – some alien civilization had colonized the entire galaxy like that.
Pamela Gay: And one of the interesting questions that are failure to ever turn these things up – brings up is, well, we know that we’re only 13.8 billion years post big bang. What if civilizations are just starting to emerge and everyone struggles with dark ages the way we did just in their own way?
It could be that even though we’re not finding these things today that someday in the future our civilization, as well as numerous others will begin to meet along these intergalactic highways.
Fraser Cain: One of the weird things to me is, is that if we do find more evidence and it does turn out to be some kinda megastructure then why hasn’t – aren’t there more? Why isn’t the entire Milky Way — why isn’t it completely colonized in the way that they’ve already done one. [Inaudible] [00:25:31] take a couple more million years [inaudible] billion tops to colonize the entire galaxy.
It’s so weird for us to only find one and not find them all over the place. And then you wonder why hasn’t our solar system been turned this way?
There’s one other technology, sort of a future technology that I think is really interesting which is the – it’s called the shgadoff thruster. I don’t know if you’ve seen this at all.
Pamela Gay: No.
Fraser Cain: But essentially it’s like a Dyson sphere but you only enclose half the star with the Dyson sphere. And then what you do is then the gravity of the sun is pulling the sun towards this –
Pamela Gay: — megastructure.
Fraser Cain: — this megastructure, this half shell. And so – but the light pressure from the star is pushing away this megastructure. And what that causes, it actually causes the sun to follow – to be pushing and following this megastructure around. And over the course of about a billion years you could pretty much reposition any star you wanted in the entire galaxy with these structures.
Pamela Gay: And this is, again, something that you see popping up in various science fiction, the idea of rearranging even the stars to the shapes you want, perhaps artisan style to form different geometric shapes. And then it starts to become a question of do other societies fear, like we do, being discovered?
There was an interesting idea put forward that the reason we haven’t found alien societies is because they use the cosmo microwave background radiation for their encryption patterns. And all of their signal disappears into the background noise. It may be that we don’t spot other civilizations because they don’t want to be spotted.
Fraser Cain: But they do still live in the laws of physics and so at the end of the day heat is the thing that you really can’t get rid of forever [inaudible] [00:27:24] –
Pamela Gay: But if you’re not moving your stars –
Fraser Cain: Yeah.
Pamela Gay: — and if you’re more of a I’m going to build giant rings that don’t circle stars entirely, you do make yourself harder to be seen.
Fraser Cain: Yeah, absolutely. And sort of one of the sort of really sort of futuristic ideas that I like to think about is this idea of [inaudible] imagine in the future we have some kind of – when the robotic overlords take over and they start to colonize the Milky Way, that they may eventually turn whatever they can get their hands on into more computing power. The term is like computrolium. And so you can imagine some kind of future robotic species reaching a planetary system, dismantling the entire thing, turning into the most efficient computer and then moving onto the next one. And literally rearranging everything within the Hubble sphere into whatever’s the most efficient computer system.
Pamela Gay: So the crazy thing about all of these notions is they require societies to be anti-environmentalism, to be against protecting our natural wonders. You can’t keep national parks and dismantle your entire planet to form a Dyson sphere. Those are incompatible ideas.
And one idea that isn’t generally discussed that could be why we’re not finding any of these things is maybe like out of the Hominid series of books maybe other intelligent societies out there aren’t out trying to war against their environment but are being more peaceably living within the environmental constraints of their world, advancing their society and their civilization without destroying everything they see.
Fraser Cain: Yeah, so I think if you enjoy these concepts, I think there’s a tremendous amount of really great science fiction to talk about it. We talked about the Ring World series which is wonderful. The Rama series from Arthur C. Clarke. You mentioned some Stevenson books.
Pamela Gay: Seven Eves is a good one. I’d also recommend the Hominid series. I’m blanking entirely on who the author is. Just to look at a comparison between how two different civilizations can adapt and parallel. Yeah, there’s a lot of different options out there for what our future can hold.
Fraser Cain: Yeah, absolutely. Hopefully then this will give everyone context as they’re looking at – looking for updates from this pretty interesting discovery. We’re not saying it’s aliens.
Pamela Gay: No. We’re saying it’s something that’s low probability.
Fraser Cain: Yeah, yeah, exactly. All right, cool. Well, thanks Pamela.
Pamela Gay: My pleasure.
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