Soz, guys. No 'alien megastructure' around Tabby's Star, only cosmic dustbunnies

Crowdfunded $107k to find system just needed a Hoover

Sorry to burst your bubble, folks, but the mysteriously dimming Tabby's Star isn't due to an "alien megastructure" after all – it's just obscured by dust, according to a paper published today.

KIC 8462852 (but Tabby's Star is catchier) was first spotted by NASA's Kepler telescope. It quickly became an object of fascination for citizen scientists working for the Planet Hunters project, hoping to discover why its brightness levels weirdly dipped for prolonged periods.

Other than that, it's a pretty regular flaming gas ball. Located in the Cygnus constellation, the F-type main sequence star is about 1,000 light years away, and is about 50 per cent bigger and 1,000oC (1,800oF) hotter than the Sun.

Several hypotheses have been suggested for the dimming light. Some people thought it was due to cold comet fragments circling the star in a highly eccentric orbit. Others believed it was a sign of extraterrestrial life trying to communicate.

Over 1,700 people donated more than $107,000 (£73,708) through a Kickstarter campaign to support a team of more than 200 researchers to observe the star at the Las Cumbres Observatory in Goleta, California, from March 2016 to December 2017.

The results have now been published in The Astrophysical Journal and suggest the dimming is all just down to, er, dust. NASA also proposed dust in uneven rings as the cause back in October last year.

"They're ancient; we are watching things that happened more than 1,000 years ago," the researchers 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."

Jason Wright, co-author of the paper and an astrophysics assistant professor at Pennsylvania State University, said: "We were hoping that once we finally caught a dip happening in real time we could see if the dips were the same depth at all wavelengths. If they were nearly the same, this would suggest that the cause was something opaque, like an orbiting disk, planet, or star, or even large structures in space."

But careful analysis showed that the intensity of the dimming of the light varied across different wavelengths.

Tabetha Boyajian, lead author of the study and an assistant professor of astrophysics at Louisiana State University, said: "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."

Although the results rule out more exotic explanations, they still raises interesting questions, Wright said. "There are models involving circumstellar material – like exocomets, which were Boyajian's team's original hypothesis – which seem to be consistent with the data we have." He said another possibility is that "nothing is blocking the star – that it just gets dimmer on its own – and this also is consistent with this summer's data."

He added: "We'd like to figure out what the source of the dimming. This first clue is that it looks a lot like dust, and is probably around the star itself."

Boyajian said the prospect was "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. If it wasn't for people with an unbiased look on our universe, this unusual star would have been overlooked." ®

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