KIC 8462852, a star around 1,200 light years away in the constellation of Cygnus has a number of nicknames, including “Tabby’s Star”, “Boyajian’s Star”, the “WTF Star”, where WTF stands for “Where’s the Flux?”, and “LGM-2”, which stands for “little green men”. The star has been unofficially named after Tabetha Boyajian, an astronomy professor in Louisiana State University. Citizen scientists combing through data collected by the Kepler Space Telescope, to identify exoplanets as part of the Planet Hunters program, initially identified unusual dips in brightness of KIC 8462852. Boyajian was the lead author of a scientific paper in which professional astronomers explored the unusual dimming events initially flagged by the citizen scientists.
The paper also explored possible reasons that caused these unusual dips in the star. The scenarios included a star that intrinsically varies in brightness, a catastrophic collision in an asteroid belt, a collision between two planets, planets with clouds of dust around them, and a number of objects in a comet like orbit around the star. Follow up observations by NASA instruments, including the Swift and Spitzer missions provided evidence that the mysterious dimming events were caused by a ton of dust, or a swarm of comets. Another explanation, proposed by Penn State astronomer Jason Wright was that there was an alien megastructure around the star.
The alien megastructure would be useful for harvesting the energies pouring out of the star, and if confirmed, would be the sign of an alien civilisation more advanced than humans. The idea of a single structure or a swarm of energy harvesting structures around a host star was proposed by Dr. Freeman Dyson, and is known as a Dyson Swarm or a Dyson Sphere. An alien megastructure, although on the bottom of the list of probably scenarios to explain the dimming events on KIC 8462852, was the one that captured the popular imagination.
Boyajian initiated a Kickstarter so that the astronomers could get the data they needed to solve the mystery. Over $100,000 was raised towards the effort, which allowed over 200 astronomers to study the star in partnership with the Las Cumbres Observatory. The observation campaign lasted from March 2016 to December 2017. Four dipping events were observed since May 2017, named Elsie, Celeste, Skara Brae, and Angkor. The updates on these dimming events were posted on a blog maintained by the team, as and when they happened.
Observing the dimming events in real time allowed the astronomers to gather the data they needed partially solve the mystery. The exact reason has not been confirmed, but some scenarios have been ruled out. If the star uniformly dimmed in all the wavelengths, then it would hint at a planet or alien megastructure being the reason for the observed occlusion. Jason Wright, co-author of the paper said, “we were hoping that once we finally caught a dip happening in real time we could see if the dips were the same depth at all wavelengths. If they were nearly the same, this would suggest that the cause was something opaque, like an orbiting disk, planet or star, or even large structures in space.” The team found that the star was dimming more in some wavelengths than others.
The new data debunks the alien megastructure theory, and provides evidence pointing to a rather mundane explanation – dust. Boyajian said, “dust is most likely the reason why the star’s light appears to dim and brighten. The new data shows that different colours of light are being blocked at different intensities. Therefore, whatever is passing between us and the star is not opaque, as would be expected from a planet or alien megastructure.” Other possible scenarios consistent with the observations include the comet swarm hypothesis, as well as an intrinsic dimming of the star that does not have a cloud of debris around it.
The finding is similar to the story of LGM-1, a pulsar discovered in 1967, officially known as PSR B1919+21. The eerie periodic flashes of the object was taken as a sign of some kind of beacon or navigational aid used by an advanced alien civilisation. Eventually, natural causes were found out to be the cause of the then strange phenomenon. Astronomers have noted the similarity between LGM-1 and KIC 8462852, which is why the star has also earned the moniker of LGM-2.
The paper is titled “The First Post-Kepler Brightness Dips of KIC 8462852” and has been published in The Astrophysical Journal Letters.