Is it a vast throng of comets, or a legion of megastructures constructed by aliens? Both are possible.
The Kepler Space Telescope has unveiled thousands of distant exoplanets by tracking their shadows across the bright surfaces of their host stars. Each time a planet passes, or transits, in front of its star, it slightly dims the star’s luminosity for a few hours or days at most, and at regular periods that match the planet’s orbit. But one star’s eccentric shine has bewildered astronomers and inflamed the imaginations of those in search of extraterrestrial intelligence.
The star KIC 8462852 sits between the constellations Cygnus and Lyra about 1500 light-years away. Like many other stars, its brightness frequently darkens from shadows cast by transiting objects. But in 2011, several “Planet Hunters” — citizen scientists recruited by Kepler’s team — tapped this star for its offbeat light pattern, quite unlike any other.
In four years of observing KIC 8462852, researchers found that the star experienced two small dimming events in 2009, a week-long 15 percent dimming in 2011, and then a series of dimmings in 2013, at one point reaching a depth of 22 percent. Even a planet as large as Jupiter would only be able to darken its host star by 2 percent at most.
Tabetha Boyajian, a postdoc at Yale, authored a paper that explains the findings. She first rules out any possibility of faulty technology or bad data, and goes on to systematically address several possibilities.
The transits couldn’t be caused by orbiting planets because they were far too erratic and dark. Instead, the pattern seems to indicate a massive, irregular shape, most likely a bevy of objects. This shape could have been a protoplanetary disc — the hulking cloud of debris that surrounds young stars before they settle down into a stable system of planets and asteroids — but the star is missing the infrared emissions that characterize such discs. The lack of infrared light also eliminates the possibility that the shape is a cloud of debris left over from an energetic collision between planets or moons. Lastly, the object must be a relatively new development, or it would have met its scorching doom at the hands of the star’s gravity by now.
So what could it be? Boyajian names a cluster of comets as the most plausible scenario. If another star recently passed close enough to KIC, it could have brought along comets that are slowly disintegrating as they orbit the star, which could explain the highly aberrant dimming patterns. But this explanation has its problems, too — it’s unlikely that this event happened in the relatively short timespan that would allow us to observe these dimmings right now. It’s also hard to imagine mere comets being able to block out a full 22 percent of a star’s light, even a huge cloud of them.
That’s why Penn State astronomer James Wright has other ideas: “Aliens should always be the very last hypothesis you consider, but this looked like something you would expect an alien civilization to build,” he told The Atlantic. While an advanced alien civilization is certainly the most far-fetched explanation, there’s nothing to disprove it yet.
Along with researchers at the Search for Extraterrestrial Intelligence Institute (SETI), Wright hopes to check out the star with a massive radio telescope. If the structures casting such dark shadows on KIC truly are some sort of alien architecture, perhaps designed to capture stellar energy, they would emit powerful radio waves detectable from Earth. If they do pick up radio waves, they can progress to the Very Large Array in New Mexico to determine whether the radio waves are coming from a technological source.
If the proposal is approved, the first observations will come as soon as January, with a follow-up planned for fall 2016. Even if we don’t end up finding aliens this time around, this discovery presents the most compelling concept of an alien civilization we have ever encountered. Regardless of the outcome of further investigations, KIC 8462852 exemplifies the most exhilarating aspect of science, particularly the cosmic variety — that we really have no idea what’s out there, and everything is possible.