Another explanation for the dimming is that KIC 8462852 is surrounded by a swarm of dusty comets.

JPL-Caltech/NASA

Star that spurred alien megastructure theories dims again

Astronomers and alien life enthusiasts alike are buzzing over the sudden dimming of an otherwise unremarkable star 1300 light-years away in the constellation Cygnus. KIC 8462852 or “Tabby’s star” has dimmed like this several times before, prompting some researchers to suggest that the megastructures of an advanced alien civilization might be blocking its light. And now—based on new data from numerous telescopes—it’s doing it again.

“This is the first clear dip we have seen since [2013], and the first we have ever caught in real time,” says Jason Wright, an astronomer at Pennsylvania State University in State College. If they can rope in more telescopes, astronomers hope to gather enough data to finally figure out what’s going on. “This could be the first of several dips about to come,” says astronomer David Kipping of Columbia University. “Many observers will be closely watching.”

KIC 8462852 was first noticed to be dipping in brightness at seemingly random intervals between 2011 and 2013 by NASA’s Kepler telescope. Kepler, launched to observe the stellar dimmings caused when an exoplanet passes in front of its star, revealed that the dimming of Tabby’s star was much more erratic than a typical planetary transit. It was also more extreme, with its brightness sometimes dropping by as much as 20%. This was not the passage of a small circular planet, but of something much larger and more irregular.

The team that made this discovery, led by Yale University astronomer Tabetha Boyajian—the star’s namesake—suggested a variety of explanations for its strange behavior, including that the star itself was variable, that it was surrounded by clouds of dust or dusty comets, or that planets around it had collided or were still forming. But KIC 8462852 hit the headlines when Wright and colleagues suggested that the star would be a good candidate to search for evidence of a large manufactured structure built by alien life.

Further studies didn’t find the infrared “glow” expected from a large object orbiting close to its star. But neither did they confirm—or refute—any other explanations. Astronomers needed to observe the star closely and take spectra—the distribution of light emitted at various wavelengths—during a dimming. For that they had to wait. Kepler stopped looking at the sky around Tabby’s star in 2013, so Boyajian and her team have been keeping an eye on KIC 8462852 with the help of a network of amateur star watchers and, more recently, with the privately run Las Cumbres Observatory, a network of 18 robotic telescopes at six sites around the world.

The first sign of the star’s recent dimming came on 24 April from Tennessee State University’s Fairborn Observatory in southern Arizona. But it wasn’t until late last week that astronomers were sure it had entered a new dip. It was 3% dimmer than its normal brightness on 19 and 20 May and is now moving back toward normal. “It looks like the dip has mostly ended,” Kipping says. “But … in the Kepler data we saw an episode of multiple dips clustered together over the span of a few weeks.” The progress of the dimming over the past few days also bears a passing resemblance to some detected by Kepler, supporting the idea that the same object is repeatedly passing in front of the star.

Observers are ready for further changes. “There’s been an enormously positive response from the community,” says Boyajian, now at Louisiana State University in Baton Rouge, with people interrupting ongoing projects to take observations of KIC 8462852. Astronomers from about a dozen different observatories managed to capture spectra from the star during the dimming. So, just what is happening around the star? Boyajian says that combining the different spectra into a coherent picture across the wavelengths may take a while. “A physical interpretation of what’s going on will take more work. But the process has begun.”