Artist's impression of an orbiting swarm of dusty comet fragments. Photo: NASA/JPL-Caltech

KIC 8462852, popularly known as Tabby’s Star, has been spotted dimming its light again inexplicably, according to multiple observatories.

The star that has been the focus of theories about alien megastructures to explain the unknown source of the light fluctuations first observed in 2009 is now in everyone’s telescopes, as astronomers and astrophysicists try to figure out the puzzle.

“Something that we’ve been waiting for, for the past four years has finally started to happen again,” said Tabby Boyajian, the astrophysicist at Louisiana State University who discovered the star, in a Youtube event over the weekend. “We couldn’t predict when it was going to happen again, so we’ve been sitting on it and monitoring it for the past few years.”

The event this time was first confirmed on May 19, and continued to fluctuate over the weekend. The event seemed to have ceased Monday – but the previous observations in 2011 and 2013 had showed similar stop-start behavior, according to Jason Wright, an astrophysicist from Pennsylvania State University.

“If the dips are periodic, I don’t think it strengthens the proof specifically of any kind of artificial construction, but it rather strengthens the proof that something is orbiting around the star,” said Boyajian. 

One preliminary calculation discussed by Boyajian and David Kipping of Columbia University over the weekend was that the periodic orbit of whatever the object is lasted some 750 days. Some astrophysicists have placed that orbit at the inner range of the potential habitable zone around KIC 8462852, they hypothesized.

“It’s been brought up before… it’s an interesting coincidence,” said Boyajian.

The artificial construction theory has captivated the imagination of the public. It holds that the dimming star that is about 1,480 light years away in the constellation Cygnus emits fluctuating light because it could potentially be surrounded by huge alien infrastructure in progress more than a millennium ago. Some proposed it could be the theorized Dyson structure, by which a civilization could surround a star with a sphere or ring to maximally harness the energy of a star.

The light from KIC 8462852 first appeared to dip in 2009, as noticed by citizen scientists. The slight decrease in brightness – about one percent for a week – appeared asymmetric, like a passing comet but unlike a planet blocking the light.

In 2011, it took another week-long plunge: down 15 percent this time. In 2013, the star flickered with odd dips that lasted 100 days.

That evidence culminated in a Penn State piece of pre-print research. It proposed in October 2015 that the unnatural dips in light could be from the alien structures around the star, as observed through the Kepler Space Telescope.

Louisiana State University scientists also published a paper in January 2016 showing the star had dimmed by a total of 20 percent over the last century, based partly on a half-million glass astronomical plates in the archives at Harvard University.

But a Vanderbilt-Lehigh-NASA study found last year, however, that the strange dips in light would not be explained by a Dyson structure, based on the physics of such a theoretical device.