About 1,480 light-years away from Earth, there is a star system glowing and dimming into strange light patterns.
The star system named KIC 8462852 - also known as Tabby's star - was detected by NASA's Kepler space telescope last year, and has been under surveillance because of its puzzling nature.
Scientists found the star system peculiar as it dims inexplicably every couple of years. Such activity is not attributed to orbiting planets, experts said. Theories as to what causes the fluctuating light have surfaced since then.
From Alien Megastructures To A Swarm Of Comets
One supposition is that the mysterious space object surrounding the star system could be an alien megastructure.
The strange light pattern suggests of a muddle of space objects that circle around KIC 8462852 in tight formation. Scientists said the mess of objects is large enough to block a significant amount of starlight.
"Aliens should always be the very last hypothesis you consider, but this looked like something you would expect an alien civilization to build," said astronomer Jason Wright of Penn State University.
However, a research paper published in November 2015 countered the theory.
Researchers from the Massachusetts Institute of Technology and Iowa University said that the most acceptable explanation for the star system's unusual dimming is the destruction of a swarm of comets.
Fragments of comet clusters could have come swiftly at an arduous orbit to form huge clouds of debris, dimming the star, scientists said. The clouds will then move, bringing back the star's brightness. This could explain the lack of strong infrared light found in investigations.
A Re-investigation Of KIC 8462852
Tabetha Boyajian of Yale University, with whom the star was informally nicknamed, led a team in September 2015 to make sense of the unusual dimming star.
Boyajian and her team looked at data from Harvard University's archival photographic plates in Cambridge, Massachusetts. These glass plates contain more than 500,000 photographs of the sky captured between 1890 and 1989.
The team wanted to see if the star system had behaved unusually in the past, but they found no evidence.
Now, astronomy and astrophysics professor Bradley E. Schaefer of Louisiana State University decided that the plates needed a re-investigation.
Schaefer tried to dig even deeper into the mystery behind KIC 8462852. He averaged the data in five-year groups to look for slow, long-term trends.
The professor found that the star system KIC 8462852 had faded by about 20 percent over a century.
"The basic effect is small and not obvious," said Schaefer.
Refuting The Comet Theory
Schaefer looked at the original photographic plates and inspected them by eye for changes, a rare skill that few astronomers possess.
"Since no one uses photographic plates any more, it's basically a lost art. Schaefer is an expert at this stuff," said Wright.
Schaefer viewed the same century-long dimming in his manual readings, and estimated that it would require 648,000 comets - each 200 kilometers or 124 miles wide - to have passed by KIC 8462852. This was completely impossible, he said.
"The comet-family idea was reasonably put forth as the best of the proposals, even while acknowledging that they all were a poor lot," said Schaefer. "But now we have a refutation of the idea, and indeed, of all published ideas."
Boyajian said this presents trouble for the comet hypothesis.
"We need more data through continuous monitoring to figure out what is going on," added Boyajian.
How about the possibility of alien megastructures? Schaefer is not convinced. He said the alien megastructure hypothesis does not match his current observations.
Schaefer said even advanced alien civilizations wouldn't be able to create or develop something capable of covering a fifth of a star in a century. Such an object should also be able to radiate light absorbed from the star as heat, he said, but the infrared signal from the KIC 8462852 appears normal.
Meanwhile, Wright said that he doesn't know how the dimming affects the alien megastructure hypothesis, aside from the fact that it would likely exclude a lot of natural explanations such as the comet hypothesis.
"It could be that there were just more dimming events in the past, or that astronomers were less lucky in the past and caught more dimming events in the 1980s than in the 1900s," added Wright. "But that seems unlikely."
In the end, Schaefer said there's no doubt that Tabby's star is behaving oddly and that something is responsible for it.
"Either one of our refutations has some hidden loophole, or some theorist needs to come up with some other proposal," he added.
Schaefer's findings are available as a pre-peer reviewed draft and submitted to the Astrophysical Journal Letters.
