Known as KIC 8462852, or Tabby’s star, it has been mystified astrophysicists for the past few months after a team of scientists noticed its light appeared to be dropping in brightness in strange ways. Suggested explanations extended from a cloud of comets to circling “alien megastructures”.
Now an analysis of historical observations discloses the star has been slowly dimming for over a century, leaving everyone scratching their heads as to the cause. The first signs of this space peculiarity came from NASA’s planet-hunting Kepler space telescope, which constantly watched the star’s area of the sky between 2009 and 2013. Most planet-hosting stars show small, even dips in light when their planets pass in front of them. But Tabby’s star dipped unpredictably throughout the four years, sometimes dropping as much as 20 per cent of its brightness.
In September, a team led by Tabetha Boyajian of Yale University, who lends the star its casual name, tried to make sense of this uncommon signal. Eventually they determined that dust from a large cloud of comets was the best explanation.
A month later, the star made headlines across the globe thanks to a paper by Jason Wright of Pennsylvania State University and his associates, who proposed that “alien megastructures”, such as satellites designed to gather light from the star, could be responsible for the signal.
Now Bradley Schaefer of Louisiana State University has exposed that the enigma goes even further. When Boyajian’s team studied the star, they looked at data from a Harvard University archive of digitally scanned photographic plates of the sky from the past century or so to see if the star had acted strangely in the past, but found nothing.
Schaefer decided this unusual star deserved a second look. He averaged the data in five-year bins to look for slow, long-term trends, and discovered that the star faded by around 20 per cent between 1890 and 1989. “The basic effect is small and not obvious,” he says.
To confirm the fade was actual, Schaefer went to Harvard to look at the original photographic plates and reviewed them by eye for changes, a skill few astrophysicists possess these days. “Since no one uses photographic plates any more, it’s fundamentally a lost art,” says Wright. “Schaefer is an expert at this stuff.”
Schaefer saw the same century-long lowering in his manual readings, and calculated that it would need 648,000 comets, each 200 kilometers wide, to have passed by the star – totally implausible, he says. “The comet-family idea was sensibly put forth as the best of the suggestions, even while acknowledging that they all were a poor lot,” he says. “But now we have a refutation of the idea, and indeed, of all published ideas.”
“This presents some trouble for the comet hypothesis,” says Boyajian. “We need more data through continuous monitoring to figure out what is going on.”
What about those alien megastructures? Schafer is unconvinced. “The alien-megastructure idea runs wrong with my new observations,” he says, as he thinks even advanced aliens wouldn’t be capable of building something proficient of covering a fifth of a star in just a century. What’s more, such an object should radiate light absorbed from the star as heat, but the infrared signal from Tabby’s star seems normal, he says.
“I don’t know how the dimming affects the megastructure hypothesis, except that it would appear to exclude a lot of natural explanations, including comets,” says Wright. “It could be that there were just more dimming events in the past, or that astrophysicists were less lucky in the past and caught more dimming events in the 1980s than in the 1900s. But that seems unlikely.”
There’s no doubt KIC 8462852 is acting bizarrely, so something must be responsible, says Schaefer. “Either one of our refutations has some hidden loophole, or some theorist needs to come up with some other proposal.”
This post was written by Usman Abrar. To contact the writer write to firstname.lastname@example.org. Follow on Facebook