Dimming star not caused by aliens, but still a mystery

Astronomers are still investigating the mystery of a star that dims in a way never seen before. But it looks like they can cross off an alien-built "megastructure" as the cause.

'It drives me a little crazy,' astronomer says. 'But it inspires scientists and the general public'

This illustration depicts a hypothetical uneven ring of dust orbiting KIC 8462852, also known as Boyajian’s Star or Tabby's Star. The star's strange dimming led some to speculate it was being blocked by an alien structure. (NASA/JPL-Caltech/R. Hurt (IPAC))

The strange star that had people talking about supposed "alien megastructures" is slowly revealing itself. And, bad news, it doesn't appear to have anything quite as interesting as something built by an intelligent civilization.

KIC 8462852 is considered an ordinary star. It's about 50 per cent bigger than our sun, about 1,000 degrees hotter and lies about 1,000 light years away. But some strange behaviour was observed in October 2015.

Working with data collected from the orbiting Kepler telescope, participants in the citizen science project Planet Hunters — who search for dips in brightness around stars, which could indicate a planet is passing in front of it — noticed that KIC 8462852 was getting dimmer. 

But, instead of dimming by around just one per cent, as is typical when a planet passes in front of a distant star, it dipped by a whopping 22 per cent.

They referred the "bizarre" findings to astronomers, and it landed on the desk of Tabetha Boyajian at Louisiana State University. 

Now, new data collected by Boyajian suggests the dimming is likely caused by something more mundane than alien beings: dust. 

Using real-time observations from ground-based telescopes, including those from amateur astronomers, Boyajian found the star — now known as "Tabby's Star" — dimmed by varying amounts depending on the colour of light.

Boyajian noted that if something like a planet were blocking the light, it would block all wavelengths by the same amount. But that's not what the new observations, to be published in the Astrophysical Journal later this year, suggest. 

"Dust blocks blue wavelengths of light much better than it does red, and so you would have a much deeper dip in the blue than in the red. And this is exactly what we see," Boyajian told CBC News in a recent interview. 

The new data revealed something else. 

"There were four major dips… then this very strange brightening for the past couple of months. Then it went back down to normal, a couple of days ago," Boyajian said.

"That's the first time we ever saw the star get bright and faint again." 

The four dips were recorded from May to the end of December and were named Elsie, Celeste, Skara Brae and Angkor. The star dimmed by about one to two per cent, nothing quite as dramatic as the 22 per cent observed by Kepler.

This isn't the first time dust has been suggested as the culprit. Last October, another study in the Astrophysical Journal also suggested it was causing the never-before-seen behaviour.

Dyson Ring? 

While scientists searched for a reasonable explanation to the original findings, some considered the possibility of an alien megastructure similar to that first proposed by physicist Freeman Dyson in the 1960s.

Dyson theorized that a sufficiently advanced alien civilization could harness the power of its host star by building a ring, sphere or similar structure around it. A Dyson Ring could account for the dramatic dip in the brightness of KIC 8462852, some theorized.

A Dyson Ring, seen in this artist's rendering, was among the theories proposed to explain the dimming. (Wikimedia Commons/Vedexent)

But Boyajian's new research says different colours of light are being blocked at various intensities. This, she concludes, means that whatever is causing the strange dips isn't opaque as one would expect with a Dyson Ring.

'A little crazy'

While the new findings are a step in helping astronomers better understand what's causing the dips in the stars brightness, it still leaves many questions unanswered, such as what caused the dust in the first place.

"The data that we have it shows that it has to be something that is semi-opaque; it's not completely opaque and you'd expect a Dyson's Sphere to be completely opaque and block the light out equally at all wavelengths," Boyajian said.

"It drives me a little crazy," Boyajian said. "But it inspires scientists and the general public to kind of wonder about space and what's out there and how much we don't know."

The Kepler telescope, data from which started all this excitement, has only surveyed less than a tenth of one per cent of the sky. But Boyajian said, that with more observations, it's possible more of these strangely behaving stars may be found.

"I think that's the coolest part of this star, as frustrating as it is, is that it kind of puts us all in our place, saying, 'Okay we don't know everything.'"

Citizen science

The initial findings about KIC 8462852 were made through Planet Hunters, but the follow-up observations were conducted through a Kickstarter campaign in which more than 1,700 people raised more than $100,000.

The money was used to book time on ground-based telescopes including the Las Cumbres Observatory in California.

Not only that, but many observations were also conducted by amateur astronomers.

"I think that was really awesome to have more than 1,700 people believe in this and say, 'Let's see what we'll find,'" Boyajian said.


Nicole Mortillaro

Senior reporter, science

Based in Toronto, Nicole covers all things science for CBC News. As an amateur astronomer, Nicole can be found looking up at the night sky appreciating the marvels of our universe. She is the editor of the Journal of the Royal Astronomical Society of Canada and the author of several books. In 2021, she won the Kavli Science Journalism Award from the American Association for the Advancement of Science for a Quirks and Quarks audio special on the history and future of Black people in science. You can send her story ideas at