So, no, probably not a mega-giant alien spaceship
Fourteen hundred light-years separate Earth from the strangest star in the sky. The light from this star flickers, like a giant neon sign drifting through the constellation Cygnus. The star dims for days or weeks, then brightens again.
Now a 200-strong team of scientists says it has arrived at an explanation for the strange behavior, thanks to an astronomy project crowdfunded on Kickstarter. It’s not aliens, as some people have speculated, but probably a cloud of dust.
In 2015, astrophysicist Tabetha Boyajian published a paper describing the starlight dips. The brightness diminished by 20 percent, according to observations from the Kepler Space Telescope. Planets block starlight when they pass across stars, like a hand waved in front of a flashlight. But even an object as huge as Jupiter can reduce a star’s brightness by just 1 percent.
“It truly is something extraordinary,” said Tyler Ellis, a PhD student who, along with Boyajian, works at Louisiana State University and studies this star and others.
The star, a yellow-white dwarf labeled KIC 8462852, was unusual enough to get a nickname, “Tabby’s Star,” after Boyajian. It earned its own Reddit forum.
And the star was so curious that Jason Wright, an astronomer at Pennsylvania State University, floated the most exotic explanation available to astronomers — aliens. Perhaps extraterrestrials had constructed a titanic array of solar panels around the star.
But when astronomers with the SETI Institute aimed their radio telescopes at Tabby’s Star, they heard no signs of life.
Meanwhile, Boyajian and her colleagues wanted to go beyond the Kepler data and watch the star dip in real time. They predicted the star would dim on a 750-day cycle. But, to be sure, they needed to continuously collect images each night, in a variety of ranges across the light spectrum.
A public Kickstarter campaign collected $100,000 to purchase telescope time at a private facility called Las Cumbres Observatory, and the hunt began through the lens of the California telescope.
The star began dimming in May. Astronomers nicknamed the event Elsie (a pun on “L-C,” for “light curves,” as well as the telescope observatory’s initials). Between May and December, the star's brightness dimmed three other times, each dip lasting several days to weeks.
The scientists probed the Elsie sequence in multiple color bands. “We had blue light, red light and yellow light,” Boyajian said, a broader range of light than Kepler’s observations.
Whatever substance exists between us and Tabby’s Star blocks more blue light than red light, as Boyajian, Ellis, Wright and other researchers reported in the Astrophysical Journal Letters on Wednesday. Planets would be unlikely to create the dips. “If you have something that is completely opaque like a planet, you would expect all the colors of the light to be blocked out at the same levels,” Boyajian said. Likewise, the discovery also rules out alien industry.
“The selective absorption of blue light has to point to dust,” Ellis said. Very small particles could block blue light’s shorter wavelengths while allowing red light, which has longer wavelengths, to escape.
If it is dust, the cloud has not spread far beyond its point of origin, the authors noted in the paper. A ring of dust around the star would constantly block starlight rather than dim light in bouts. And the amount of dust needed is more than Tabby’s Star should produce.
So even with a natural cause for its dips, Tabby’s Star is still mysterious.
“We are not done,” Ellis said. “We are certainly not done with this star yet.”
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