Astronomers have their best solution yet to the mysterious alien megastructure star

• Since 2015, astronomers have been trying to find the cause of Tabby's Star's mysterious behavior. The star keeps dimming in an oddly sporadic pattern, and has overall gotten 10% less bright in just a century.
• Some scientists have suggested an alien megastructure or a massive swarm of comets may be to blame.
• In 2019, a team of astrophysicists at Columbia University proposed a different culprit. The star may have stolen icy moons from an orbiting planet. Over time, radiation dissolved these moons, creating a dusty cloud that blocks some of the starlight.
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Following is a transcript of the video.

Narrator: In 2015, astronomers noticed something ...strange going on nearly 1,500 light-years from home. A star named KIC 8462852, aka Tabby's Star, kept dimming. As though something was passing in front of it. Since then, scientists have been trying to figure out what that something might be. A swarm of comets flying by, en masse? An alien megastructure? Then, in 2019, a team of astrophysicists proposed a new, more plausible explanation. That might finally solve the mystery of Tabby's Star.

Narrator: There are really TWO mysteries centered on Tabby's Star. First, the star keeps brightening and dimming in a bizarrely sporadic pattern. While very young stars will occasionally behave like this astronomers have never seen it in a star of Tabby's age. Second, the star is slowly, but surely, getting dimmer over time in a steady decline that astronomers have never observed in another star of its type. Clearly, something fishy is going on. Some researchers have suggested an advanced alien civilization is to blame.

If aliens built a megastructure called a Dyson Sphere to siphon off the star's energy that could explain how the star is a whopping 10% dimmer than it was just a century ago. But there are some holes in that idea. For one, you'd expect an orbiting megastructure to make regular, predictable trips around the star. Just like the International Space Station makes regular trips around the Earth. But so far, there's no clear evidence that the dips occur on a consistent schedule. Plus, when it comes to any theory about advanced alien civilizations.

Brian Metzger: It's a little hard to test it.

Narrator: He studies what he calls

Metzger: Things that go bump in the night.

Narrator: Or strange phenomena in the universe - including the odd behavior of Tabby's Star. Metzger says another theory has problems as well. You see, some experts suggest a massive swarm of comets is the real culprit. This has the advantage that - unlike aliens - we're positive comets exist and if they were orbiting the star, they'd explain the random blips. But ...

Metzger: A lot of the explanations run into the problem of "why is this relatively rare, why don't other stars show this behavior.

Narrator: Basically, there'd need to be something special about Tabby's Star to attract so many comets to congregate at the same place, at the same time. But as far as astronomers can tell, Tabby's Star is just like any other star of its type. Luckily, Metzger and his team may have a new solution. In 2019, they published a paper in the Monthly Notices of the Royal Astronomical Society that argued for a different culprit: The dusty remains of a dying moon. According to Metzger's models, a gas giant may have orbited the star millions of years ago. And like Jupiter and other gas giants, it hosted a few icy moons.

Now, the planet and its moons would have continued to orbit Tabby's Star to this day if not for one problem: Metzger says a second, nearby star may have exerted a tiny gravitational pull on the planet. Over time, it slowly tugged the planet out of its orbit and towards Tabby's Star. Until, eventually, the planet fell in and was destroyed. But the planet's moons may have escaped this fate instead getting trapped into orbit by Tabby's gravity. Over time, the constant radiation could have melted off chunks of these icy moons resulting in a colossal cloud of moon dust around the star. Now, this plan makes sense for a number of reasons. First,

Metzger: Dust - as small, particulate grains - is a really effective way to block the light of a star.

Narrator: Unlike an alien superstructure, dust floats around in a blob that's constantly morphing and changing its shape, which could explain the irregular dips. And, if enough of it accumulated around the star over time it could lead to that mysterious 10% dimming astronomers observe. The moon part of Metzger's hypothesis works well, too.

Metzger: You need an object that's massive, that has a lot of material that it could survive for a very long time, that it could feed this giant cloud of debris.

Narrator: Meanwhile, you'd need a remarkably large swarm of unusually giant comets in order to get the same job done.

Metzger: We would need something much bigger than an ordinary comet to explain the dipping around Tabby's Star.

Narrator: Plus, unlike an alien machine, we see moons all the time. And, while we haven't seen this EXACT scenario before it's based on something we have observed with Jupiter-like planets.

Metzger: We have lots of evidence from other planets that Jupiter's can be driven into their stars. If you think Jupiters are being driven close to their stars, you have to say what happened to their moons.

Narrator: So, mystery solved? Well, not quite. While Metzger says he's happy with his team's explanation, he still has plenty of work ahead of him.

Metzger: I think it's important to move beyond what we're working on now and make predictions that can be tested.

Narrator: After all, theoretical models only get you so far. That being said, it's still probably not aliens.