You Knew This Day Was Coming. Alien Megastructures Ruled Out for Tabby’s Star. Dust is the Culprit

In September of 2015, KIC 8462852 (aka. Tabby’s Star) captured the world’s attention when it was found to be experiencing a mysterious drop in brightness. In the years since then, multiple studies have been conducted that have tried to offer a natural explanation for this behavior. In lieu of one, there’s been plenty of speculation as to what could be causing the dimming effect – including the controversial “alien megastructure” theory.

Unfortunately, after years of excitement and speculation, the scientific community may have finally driven a nail into this theory’s coffin. According to a new study by a team of over 100 astronomers, and led by Assistant Professor Tabetha Boyajian – who made the original discovery – it now appears likely that KIC 8462852 (aka. “Tabby’s Star”) is being partially obscured by dust and not – I repeat, NOT – an alien megastructure.

The study, titled “The First Post-Kepler Brightness Dips of KIC 8462852“, recently appeared in The Astrophysical Journal Letters. Led by Prof. Boyajian from Louisiana State University in Baton Rouge, the team consisted of astronomers from the Instituto de Astrofísica de Canarias (IAC), the University of La Laguna in Spain, the American Association of Variable Star Observers, and the Center for Exoplanets and Habitability at the University of Warwick.

The study was also made possible thanks to a Kickstarter campaign that Prof. Boyajian and her colleagues launched in 2016. The campaign successfully raised more than $100,000 to pay for observation time so that Boyajian and her colleagues could gather more data on KIC 8462852. In partnership with the Las Cumbres Observatory, they gathered spectroscopic data on the star using a network of telescopes from all over the world.

What they found was that the dimming pattern was most likely caused by a cloud of obscuring dust around the star, as evidenced by the way light coming from the star being unevenly blocked. As Prof. Boyajian explained in a recent LSU press release:

“Dust is most likely the reason why the star’s light appears to dim and brighten. The new data shows that different colors of light are being blocked at different intensities. Therefore, whatever is passing between us and the star is not opaque, as would be expected from a planet or alien megastructure.”

The theory that KIC 8462852 might be surrounded by an obscuring dust cloud is not entirely new. In fact, a circumstellar debris disk was one of several theories offered in the past two years for the star’s mysterious dimming patterns. Other suggestions included shattered comets or asteroids, the presence of a giant planet, a planet with rings, or even a planet that had been consumed in the past.

LSU Astronomer Tabetha Boyajian (center) and her students and research staff. (Left to right) Robert Parks, undergraduate student Rory Bentley, Assistant Professor Tabetha Boyajian, PhD candidate Tyler Ellis, undergrad Katie Nugent, Professor Geoff Clayton and graduate student Emily Safron. Credit: LSU

However, none of these possibilities were ironclad, and all were based on the first few recorded dips in star’s light curve. In contrast, Prof. Boyajian and her team closely observed KIC 8462852 from the the Las Cumbres Observatory for a fourteen-month period, which ran from March 2016 to December 2017. This allowed them to witness four additional episodes where the star’s light dipped, beginning in May of 2017.

Those who supported the crowdfunding campaign were able to nominate and vote on names for these episodes. The first two dips were named Elsie and Celeste, while the last two were named Skara Brae and Angkor – after ancient lost cities in Scotland and Cambodia. As the team indicated in their study, the first two names held special significance for the team and KIC 8462852 itself:

“The name Elsie is a play on words with ‘L + C,’ short for ‘light curve,’ and is also a wink and a nod to the ‘L’as ‘C’umbres Observatory, for making the project happen. This dip [first] appeared to have a slow decline with a quick rise, which is close to a mirror image of Elsie, which had a quick decline with a slow rise. Elsie (or ‘L C’) in reverse is ‘C L’ or ‘ciel,’ which means ‘sky’ or ‘heavenly’ in French. ‘Celeste’ is the original Latin name from which ‘ciel’ is derived.”

Meanwhile, the dips that bore the name of lost cities were a reference to the activity (also ancient by human standards) astronomers have been observing from this distant star. “They’re ancient; we are watching things that happened more than 1,000 years ago,” the team wrote. “They’re almost certainly caused by something ordinary, at least on a cosmic scale. And yet that makes them more interesting, not less. But most of all, they’re mysterious. What the heck was going on there, all those centuries ago?”

One of the many robotic telescopes part of the Las Cumbres Observatory used to observe Tabby’s Star. Credit: LSU

In addition to providing the first truly solid explanation for Tabby’s Star, this study is also an indication of how the field of astronomical research is changing. Basically, it was conducted by experts in the field who conducted an observation campaign using state-of-the-art instruments. However, it would not have been possible without the engagement and financial support it received from the public.

The original discovery was also possible thanks in large part to citizen scientists and planet hunters, who helped sift through the massive amounts of data obtained by the Kepler mission. As Boyajian herself indicated, the assistance of the public is what made the biggest difference:

“If it wasn’t for people with an unbiased look on our universe, this unusual star would have been overlooked. Again, without the public support for this dedicated observing run, we would not have this large amount of data… It’s exciting. I am so appreciative of all of the people who have contributed to this in the past year – the citizen scientists and professional astronomers. It’s quite humbling to have all of these people contributing in various ways to help figure it out.”

Of course, there is much work to be done and many more questions that need to be answered. But in the meantime, it seems that the single-greatest question about Tabby’s Star – a natural cause or possible evidence of alien activity? – has been tentatively resolved. For those who were hoping that it might be the long-awaited resolution to Fermi’s Paradox I think it’s fair to say we all knew this had to happen sooner or later.

And in the end, is it not better to know that strange and mysterious events have a natural explanation, rather than to not know one way or another? Sure, if you don’t know, it leaves you free to speculate and think what you want, but that’s hardly a scientific attitude. And if we ever want to find evidence of extra-terrestrial intelligence, we need to be able to distinguish natural phenomena from something unnatural.

Remember Carl Sagan’s famous words: “The absence of evidence is not the evidence of absence”? Well, that works both ways! In the meantime, be sure to check out this video of Prof. Boyajian’s TED Talk about the star that bear’s her name:

Further Reading: LSU, The Astrophysical Journal Letters,