Cosmic dust, not 'alien megastructure,' veils mysterious star

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NASA image obtained January 3, 2018 shows an illustration of a star behind a shattered comet. Observations of the star KIC 8462852 by NASA's Kepler and Spitzer space telescopes suggest that its unusual light signals are likely from comet fragments

It's been called the "most mysterious star in the universe," bigger than the sun and yet brightening and dimming in an odd way that suggested to some an alien megastructure might be circling it.

But a study out Wednesday, compiled by more than 100 scientists who have been observing the star named KIC 8462852, puts the alien rumors to rest.

"Dust is most likely the reason why the star's light appears to dim and brighten," said lead author Tabetha Boyajian, assistant professor of physics and astronomy at Louisiana State University, for whom "Tabby's Star" is nicknamed.

"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 initial discovery of the star was made with the help of NASA's planet-hunting space telescope, known as Kepler.

Kepler detects planets by tracking moments when a star's light dims as an object passes in front of it.

The unusual dips in brightness in Tabby's Star -- more than 1,000 light-years away, about 50 percent bigger and 1,000 degrees hotter than the sun -- aroused global interest.

Citizen scientists, known as the Planet Hunters, were the ones who discovered the star's strange behavior, by sifting through massive amounts of data from the NASA Kepler mission.

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

- New era in astronomy -

More than 1,700 people donated some $100,000 through a Kickstarter campaign to study it further.

Astronomers at the California-based Las Cumbres Observatory watched it closely from March 2016 to December 2017.

"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," said co-author Jason Wright, assistant professor at Pennsylvania State's department of astronomy and astrophysics.

"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."

The team indeed found four episodes when the star's light dipped, beginning in May 2017.

Even though the team has ruled out any massive alien construction as the cause of dimming, "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."

Researchers say the experiment is indicative of a new era in astronomy, in which crowd-sourcing and citizen scientists help fuel new discoveries.

"We're gathering so much data on a single target," said Tyler Ellis, a doctoral candidate at Louisiana State University who was among those studying this star.

"This project is reflective of changes in astronomy with the access to this flood of data."

The report is published in The Astrophysical Journal Letters.