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Mysterious dimming star: alien megastructure theory debunked

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Scientists are getting closer to solving the mystery of a distant star which sporadically dims and brightens in an unusual fashion.

Nasa’s Kepler Space Telescope originally discovered the strange star, dubbed KIC 8462852 or ‘Tabby’s Star’, in 2015 and explanatory theories circulating have ranged from it having swallowed a nearby planet, to an unusually large group of comets orbiting the star, or an alien megastructure.

Now, a team of more than 200 researchers believe they are one step closer to understanding the mystery behind it which proved so compelling that more than 1,700 people donated over $100,000 through a Kickstarter campaign in support of dedicated ground-based telescope time to observe and gather more data on the star through a network of telescopes around the world.

‘Tabby’s Star’ is about 50 per cent bigger and 1,000 degrees hotter than our Sun and approximately more than 1,000 light years away.

“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” said Penn State University Professor Jason Wright.

Instead, the team found that the star got much dimmer at some wavelengths than at others.

“Dust is most likely the reason why the star’s light appears to dim and brighten. The new data shows that different colours 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,” said Louisiana State University's Tabetha Boyajian.

The scientists closely observed the star through the Las Cumbres Observatory from March 2016 to December 2017. Beginning in May 2017, there were four distinct episodes when the star’s light dipped.

“They’re ancient; we are watching things that happened more than 1,000 years ago,” the authors of a paper on the star 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.”

The method in which this star is being studied - by gathering and analysing a flood of data from a single target - signals a new era of astronomy. Citizen scientists sifting through massive amounts of data from the Nasa Kepler mission were the ones to detect the star’s unusual behaviour in the first place.

The main objective of the Kepler mission was to find planets, which it does by detecting the periodic dimming made from a planet moving in front of a star, hence blocking out a tiny bit of starlight. The online citizen science group Planet Hunters was established so that volunteers could help to classify light curves from the Kepler mission and to search for such planets.

“If it wasn’t for people with an unbiased look on our universe, this unusual star would have been overlooked,” Boyajian said. “Again, without the public support for this dedicated observing run, we would not have this large amount of data.”

Now there are more answers to be found. “This latest research rules out alien megastructures, but it raises the plausibility of other phenomena being behind the dimming,” 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.” Wright also points out that “some astronomers favour the idea that nothing is blocking the star - that it just gets dimmer on its own - and this also is consistent with this summer’s data.”

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