Alien megastructures around this star were dust in the interstellar wind

For the last two years, astronomers all over the world have been eagerly observing what is hailed as “the most mysterious star in the Universe,” a stellar object that wildly fluctuates in brightness with no discernible pattern — and now they may finally have an answer for its weird behavior. Scientists are fairly certain that a bunch of dust surrounding the star is to blame. And that means that the more tantalizing explanation — alien involvement — is definitely not the cause.

It’s the most solid solution yet that astronomers have come up with for this star’s odd ways. Named KIC 8462852, the star doesn’t act like any star we’ve ever seen before. Its light fluctuations are extreme, dimming by up to 20 percent at times. And its dips don’t seem to repeat in a predictable way. That means something really big and irregular is passing in front of this star, leading scientists to suggest a number of possible objects that could be blocking the star’s light — from a family of large comets to even “alien megastructures” orbiting the star.

The idea of aliens drummed up so much public interest that more than 1,700 people donated $100,000 to a Kickstarter campaign to fund further observations of the star. From March 2016 to December 2017, astronomers at the Las Cumbres Observatory watched with telescopes all over the world, observing four of its weird dips. The campaign collected oodles of data, which still needs to be parsed out thoroughly. But early analysis, detailed today in Astrophysical Journal Letters, found that whatever is blocking the star’s light is definitely not opaque and most likely filtering the light as dust does. So that puts the alien megastructure theory to rest.

This doesn’t mean astronomers are done learning about the star, though. It’s still unclear what is causing all this dust and whether or not the dust is orbiting the star or if it’s coming from somewhere else. “Weird stars that have dust coming from somewhere isn’t as much of a headline grabber,” Jason Wright, an astronomer at Penn State University and one of the 200 authors on the paper, tells The Verge. “But obviously there’s a still lot of interest to figure out this weirdo star.”

KIC 8462852 first came to the attention of the astronomy world thanks to NASA’s Kepler spacecraft, which searches for planets around distant stars. Astronomer Tabetha Boyajian and her team from Louisiana State University were combing through Kepler’s data and found that the spacecraft had observed this star and recorded its strange behavior. They couldn’t come up with an easy explanation for it either. An orbiting planet wouldn’t dim the star as much as it was dimming, and a planet would cause periodic dips each time it passed between the star and Earth.

Then in 2015, Wright suggested a fun, but very unlikely scenario: perhaps large alien megastructures are orbiting the star to collect solar power for an advanced civilization. Maybe the star was surrounded by a Dyson sphere, a theoretical object that encompasses a sun essentially gathering all of its energy. The suggestion caused an explosion of interest online, prompting people to give KIC 8462852 a new nickname: the “alien megastructure star.”

Aliens are always the last possible scenario that astronomers consider, but there still wasn’t a good explanation for KIC 8462852. So during last year’s observation campaign, astronomers made sure to measure the star’s light in different wavelengths — the peaks and valleys light travels over certain distances. Red and blue light, for instance, have different wavelengths: blue light is much shorter and compressed whereas red light is more elongated and stretched out. Measuring KIC 8462852’s dimming light in different wavelengths can tell scientists more about any objects that might be passing by. Certain types of materials will filter light in different ways.

If an opaque object, like a planet or alien megastructure was passing in front of the star, it would block both red and blue light the same amount, says Wright. However, the astronomers found that blue light was blocked much more than red light during the star’s dimming. Since blue light has much shorter wavelengths than red light, it’s much more easily blocked by smaller materials, such as fine grains like dust. “This is characteristic of something that’s filtering the light,” says Wright. “That’s what you get when you have dust.”

That means one of the long-held theories about KIC 8462852 may be true: a large group of comets are circling the star, producing a huge amount of gas and dust that is filtering the star’s light. But astronomers still don’t know for sure if comets are the true dust source. Wright has what he calls a “dark horse” idea: the dust doesn’t surround the star at all but is actually around a nearby black hole that is passing between KIC 8462852 and Earth.

But above all, the alien megastructure star may need a new nickname, since it seems clear that we haven’t stumbled on an advanced alien culture. There’s still quite a lot of information to go through, though, which could ultimately hold clues as to what’s causing this star’s bizarre twinkle. “We’re swimming in data,” says Wright. “It’s going to take us a long time to get through it all.”

(THE VERGE)