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SYFY WIRE Bad Astronomy

Update: SETI Sees No Alien Signals From Weird Star

By Phil Plait

A few weeks ago, I (and a zillion other people) reported on a star about 1,500 light-years away that was acting … weirdly. It was showing irregular dips in its light, sometimes dropping in brightness by more than 20 percent.

Stars don’t generally do this. In this case, KIC 8462852 (thankfully nicknamed Tabby’s Star, after astronomer Tabetha Boyajian who led the research on it) was pouring the weirdness on pretty thick. The dips were not coming at regular intervals, as would be expected if it had a planet or planets orbiting it, periodically blocking its light. It couldn’t be a planet doing this anyway, because no planet is that big. It wasn’t another star, since we’d see that. Clouds of comets were a pretty good guess, but the data don’t fit that perfectly either.

Some media were very quick to jump on the idea that it might be aliens—the idea being that an advanced civilization might be building huge (really huge, like hundreds of thousands of kilometers across huge) solar arrays to collect starlight for power, and it was these that were blocking the star from our view, causing the dips.

This is unlikely, to say the least. Even Jason Wright, the astronomer who came up with the idea, gave it pretty long odds. But hey, scientists like to play with ideas. If it were aliens building huge megastructures, could we detect them?

Maybe. Radio waves are easy to make, can be coded to contain lots of info, and travel at the speed of light. If they communicate with each other that way, maybe we could detect some of that radio chatter as it leaks away from them. Or maybe they used really powerful telescopes, saw our planet all green and oxygeny, and sent a message our way—bearing in mind that if they saw us from 1,500 light-years away and sent us a message we’d receive now, they would’ve had to send that beam in the year 515 AD, when radio was still 1,400 years in our future. That makes this unlikely, too.*

Still, it can’t hurt to check. We have radio telescopes all over the planet, so why not take a peek and see?

That’s just what the folks at SETI did. After all, it’s their job: They’re the search for extraterrestrial intelligence! So they pointed some of the dishes that make up the Allen Telescope Array located in extreme Northern California skyward, listening in for any signal from the purported aliens.

And what did they find? Well, nothing. Sadly, no beamed message to us, no leaked radio from the extraterrestrial equivalent of late night talk shows, no ship-to-ship communications, nada.

What does this mean?

Well, not a whole lot. This is a case where getting a positive result means a lot (aliens!), but negative doesn’t really do much for you. As my friend, SETI astronomer Seth Shostak put it, “The history of astronomy tells us that every time we thought we had found a phenomenon due to the activities of extraterrestrials, we were wrong. But although it’s quite likely that this star’s strange behavior is due to nature, not aliens, it’s only prudent to check such things out.” 

He’s right. As I wrote before, the bet that this star’s behavior is due to aliens is a long shot, but it only takes a teeny bit of effort to check it out. If it had cost millions of dollars and taken precious time away from other projects that would have been a different matter. But it doesn’t, and it didn’t, so efforts are ongoing.

I’ll note that on the Centauri Dreams blog, Paul Gilster brings up an interesting point.* We know the star rotates rapidly (we can see that in the data), and that means it may very well be oblate, nonspherical. This can affect the way the star shines; instead of being a uniform brightness across its disk, the star can have dark edges, or bands across it, or other features. This could explain some of the weird shapes to the brightness dips seen in the data; an object passing in front of the star might block a dark part first and a bright part second, causing asymmetries in the dips.

It’s a good thought, and I like it. However, it doesn’t quite cover all the bases; it’s still incredibly difficult to get such monumental dips in the star’s brightness. However, it does get us a step closer to a natural solution; maybe it’s oblate star + weird comets + X.

What’s X? Something we haven’t thought of yet. “Aliens” is still way down on that list, and it’s far more likely we’re seeing a mishmash of just odd, unusual stuff happening at this star.

In the meantime, more observations are being made, which I enthusiastically support. While it’s most likely not aliens, X is still something really interesting. We’ve never seen anything quite like this star before, so the more we scrutinize it, the better.

*Correction, Nov. 6, 2015: This post originally misspelled Paul Gilster’s last name. I also originally wrote that the aliens would've sent a message in the year 615. It's also worth noting that the light they'd have seen from us when they sent any message would have been from 1,500 years further past, so they would have been seeing us as we were sometime around 900 BC.

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