Alien Megastructures and Dark Matter: How Imagination Fuels Science

Comet Family Blocking Light of Faraway Star
Artist's illustration showing a shattered comet passing in front of a star — perhaps the leading explanation at the moment for the strange dimming observed in the KIC 8462852 system. (Image credit: NASA/JPL-Caltech)

Michelle Thaller is an astronomer who studies binary stars and the life cycles of stars, and is deputy director of science communication at NASA. She contributed this article to's Expert Voices: Op-Ed & Insights.

Scientists are just the same as everyone else. On most days, you could be out walking around town, doing a little grocery shopping, and not even realize that you passed right by a scientist. I say this, only partially jokingly, because I am often amazed at the assumption that we (speaking as a scientist) think differently, feel differently and generally do not participate in the same flow of life as other people. I remember, at a recent public talk, someone asked a question that roughly came out like: "If scientists discovered [insert threatening phenomenon here], would they tell us?" I had to turn around and ask, "Who is the 'us' here?" We scientists are part of "us."

Such issues came up recently when the news about the frustrating, and intriguing, object KIC 8462852 came to the fore. It's a star from which NASA Kepler spacecraft measured huge and intermittent drops in brightness, and despite some months of dedicated study, scientists haven't been able to add much to the discussion. But the gist of the comments I got from people, both in person and via the interwebs, was disbelief. People couldn't accept that, among other much (much) more likely natural phenomena, one of the possible explanations put forth by serious scientists was that this might be a giant artificial structure built by aliens. This made people's jaws drop. Isn't that idea too imaginative, too based in fantasy to be something scientists should consider? 

These reactions made me think hard about the respect I have for unbounded imagination, and how useful, if used correctly, it can be for science. 

A most curious star

To back up a bit, this intriguing star was observed by the Kepler spacecraft, which is being used to search for signs of planets around other stars using the transit method. 

One of the simplest, most direct ways of finding exoplanets is to measure the amount of starlight that drops off when a tiny, distant planet swings into astronomers' line of sight and creates a minuscule version of a partial solar eclipse. Usually, these "transits" are pretty clear-cut affairs. 

Any planet large enough to be detected this way is spherical, and produces a nice, regular light curve as it passes in front of its star. Also, if you have indeed found a planet, you expect it to come around again and again, hopefully in a regular, predictable orbit. The predictability is key; a random drop in brightness could be due to a starspot (yes, the distant equivalent of a sunspot), or even a passing comet. Find a nice, clear drop in stellar brightness that comes around like clockwork, and you can call it a detection of a new exoplanet. 

And that's where KIC 8462852 got so weird. For one thing, whatever is blocking the light from that star is blocking a whole lot of it, up to 22 percent of the starlight. Even giant planets block only a small percentage of a star's light. Any planet big enough to directly block a fifth of a star's light would most likely be so large that it would have to be another star. Which we would see. 

The light variations aren't periodic, either; astronomers haven't found any clear pattern to them, and the light curves are very strange, as if whatever is blocking the light is not spherical. Some astronomers have proposed a huge, irregular cloud of comets orbiting the star, but even this doesn't work very well as an explanation. It's hard to imagine a swarm of comets blocking that much light, and there is no hint of these comets in the infrared, where even cold, icy objects glow like lightbulbs. We've seen other comet swarms around nearby stars already, and we should have been able to pick up the radiation from a big one around KIC 8462852.

The lead author on the KIC 8462852 detection, Tabetha Boyajian, an exoplanet scientist at Yale University showed her measurements to her colleague, Jason Wright, an astronomer at Penn State University, who had an amazing suggestion: Could these dips in the light be caused by a vast, engineered structure built by a technologically advanced civilization? 

All involved scientists, including those two astronomers, said that this conclusion is highly unlikely — but that maybe it shouldn't be discounted. Maybe scientists can at least throw it on the heap of possible explanations about what's going on here. And that is where my friends' stereotypes of cold, linear, logical scientists, really came into the fore and showed me just how wrong their assumptions about scientists can be. Here is the accusation: This seemed like an awfully imaginative idea for a scientist to propose.

I had a chance to talk to my friend, well-known astronomer and science communicator Phil Plait, about this when he was my guest on Orbital Path, a podcast I do for PRX. During the conversation, we mused not only about the fabulously unlikely scenario of an alien superstructure, but also how wonderful it was to allow ourselves to imagine that it might be the real answer. 

The idea of a huge alien structure around a star is nothing new; in fact, it was proposed by a very serious, if somewhat eccentric astronomer named Freeman Dyson. He proposed, many decades ago, that an advanced civilization, with tremendous energy needs, might build a huge orbiting shield of solar panels around a star, with the intent of soaking in as much free energy as possible. Some people visualized this as a continuous, closed-in sphere, but Dyson's idea was more of a fleet of disconnected, vast solar-array structures. 

The idea came to be known as a Dyson sphere , and when I was working at the Infrared Processing and Analysis Center at the California Institute of Technology, well-respected scientists would sometimes propose observing programs to look for the infrared signatures of such structures. And make no mistake — Boyajian and Wrigher are also serious, excellent scientists. These are not tinfoil-hat types, but instead are careful scientists who are looking for any possible explanation their data would support. And I feel the need to put some very clear caveats in here. I would bet my mortgage that we are not looking at a Dyson sphere, but instead some kind of a much less romantic — but still fascinatingly unusual — debris disk.

Using the imagination, always

Phil and I agreed that, as scientists, we are allowed to be imaginative. We certainly can't currently say that we have discovered an alien civilization or even that one is a likely explanation for the data. But it's not an impossible explanation. And for a few minutes, Phil and I allowed ourselves a little flight of fantasy. 

What if, somehow, we could prove the light dips were caused by an artificial structure? What if there really was a star you could look at in the sky, and know that there was an advanced alien civilization around it? Can you just imagine dragging your little telescope out to a dark field, getting a shimmering point of light in the view field (it looks like any other star if you're not measuring the brightness very accurately over many weeks) and allowing yourself that shiver of ecstasy and a little fear in knowing you are looking at aliens? Real aliens. Perhaps there are even alien astronomers looking in our direction tonight? 

As strange as that may sound, such thoughts feel very human to me. Solar panels and giant orbiting space stations are things people can conceive of today, even without the engineering know-how to build such structures. It's just a logical next step of technology, but that's usually not the way things play out. Picture the ancient Egyptians imagining a pyramid 100 stories high, but not imagining a smartphone. Someone, the idea of a Dyson sphere lacks, well, imagination. It is an extension of our very human technology.

Being a scientist means being very aware of controlling your conclusions, even your emotions, when dealing with things that you really want to be true. Your hopes and dreams about the universe have no bearing on the data you collect and honestly interpret, nor should they ever. 

But scientists are also deeply imaginative people. Who else becomes an astronomer? Almost to a person, we scientists are fans of science fiction and fantasy. And for my part, I became an astronomer mainly because of the beautiful stories the universe has to tell us. True tales of how the atoms that make up humans were forged in stars, or how the water in human blood, sweat and tears was brought here largely by asteroids and comets. I loved the stories, couldn't get them out of my head. 

This Hubble Space Telescope composite image shows a ghostly "ring" of dark matter in the galaxy cluster Cl 0024+17. (Image credit: NASA, ESA, M.J. Jee and H. Ford (Johns Hopkins University))

I have respect for scientists allowing themselves to be a bit taken away by imagination. I have a feeling that's how science advances. Yes, there is the classic scientific method of forming hypotheses and designing experiments to test those ideas, but there is also a large dose of intuition and "what if this happened…?" Honestly, maybe there's more of this in science than many scientists would like to admit. 

A darker look at dark matter

Recently, I read Lisa Randall's book, "Dark Matter and the Dinosaurs" (Ecco, 2015), in order to interview her for my podcast. Randall bases the book on an astounding conjecture: Is it possible that the dark matter in the galaxy is not distributed in a ghostly, amorphous halo, but instead has actual structures, namely, a dark disk hidden inside the main stellar disk of the Milky Way? 

As the solar system orbits the galaxy and bobs up and down through the disk, Earth may periodically pass through a phantom disk of enhanced gravity, capable of pulling large objects out of the Oort cloud or Kuiper Belt and hurling them in toward the sun and Earth. Might there be a cycle of mass extinctions linked to the motion of the sun around the galaxy, caused by an unseen disk of dark matter screwing with the orbital dynamics of the outer solar system?

At first, this idea seemed preposterous, but it was fun. To begin with, there is no compelling evidence that past mass extinctions fell into any sort of clear pattern of timing, but that's hardly proof of a negative. Perhaps some passages through the dark disk fail to send many dangerous objects into the Earth's path, or the planet was just lucky to miss them. The other objection is what the current understanding of dark matter (such as it is) suggests to us: that this material doesn't interact with itself the same way regular matter does. 

The familiar sort of matter — it's kind of hard to call it "normal matter" since it is well in the minority, mass-wise, for the universe — has all sorts of forces acting on it. Not only do people feel gravity from other matter, but they interact electromagnetically, throwing photons back and forth to heat up and cool down. You need that in order to form a disk like the Milky Way's. 

In the early history of galaxy formation, gravity brought gas and dust together, and the conservation of angular momentum spun it up. But then, cooling had to happen; nothing can collapse into a disk unless it can lose energy, radiating away the heat of the interactions. Preliminary data about dark matter suggests that it doesn't do this: Scientists have observed collisions between galaxy clusters in which the dark matter seems to just pass on through the whole train wreck. It doesn't smash into itself; it doesn't heat up. It just keeps on going. If that is indeed the case, then dark matter should mainly be found in a sparse, extended halo, just barely bound to the gravity of the galaxy.

Now, very recently, scientists wondered if, in fact, there is evidence that dark matter interacts with itself. A recent paper asserts that given simple gravitation, dark matter haloes should have denser cores than what astronomers observe. (That paper, from Manoj Kaplinghat is titled "Dark Matter Halos as Particle Colliders: Unified Solution to Small-Scale Structure Puzzles from Dwarfs to Clusters" and appears in the journal Physical Review Letters.) Perhaps there is some sort of heating that puffs up the haloes. 

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This is more exciting and weird than you would think, because if dark matter does have an electromagnetic-type force acting on it, that constitutes an entirely new form of radiation. Famously, dark matter does not radiate any sort of light, no photons at all. So if dark matter can lose energy through radiation, there must be a sort of "dark light" that scientists have been entirely unaware of.

So you think scientists lack imagination? I'll raise you a disk of self-interacting dark matter, glowing with completely invisible light that may have lobbed a comet at the Earth 65 million years ago, killed most of the dominant life forms on the planet and allowed for your tree-shrew great-great (great, great, etc.) grandmother to get a leg up on competition for resources. 

Or there's an alien-made superstructure millions of miles across gathering energy to power technology today's humans can't possibly imagine, coincidentally making a distant star twinkle. Think about the leap of imagination that entails. 

Scientists can imagine some pretty preposterous things, like a universe that is mostly made up of a form of matter that passes right through people like a ghost through a wall — and that bit turned out to be completely true! 

Science is so much better than pure fantasy. The reason scientists allow themselves to imagine such things is that these ideas best match our data, and slowly we form a new view of reality. So let's tip our hats to Albert Einstein, who reminds us that the universe is not stranger than we do imagine, but stranger than we can imagine. 

About the Podcast: Orbital Path with Michelle Thaller takes a look at the big questions of the cosmos and what the answers can reveal about life here on Earth. It comes from podcast powerhouse PRX, with support from the Sloan Foundation. Learn more and subscribe at

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