Kepler's "Alien Megastructure" star has been dimming at an unprecedented rate.

The KIC 8462852 was observed by NASA's Kepler mission and has become famous among scientists when it was suspected that its flickering signals could be a result of an alien megastructure.

While further observations of the star found no signs of aliens, the luminosity of KIC 8462852 - unofficially named "Tabby's Star" after astronomer Tabetha Boyajian who discovered the signals - has been diminishing, causing more confusion among astronomers.

In a new study published to the arxiv, astronomers Ben Montet of the California Institute of Technology (Caltech) and Joshua Simon of the Carnegie Institution described the results of a new photometric analysis of Tabby's Star. The scientists examined the full-frame images collected during Kepler's four-year observational campaign and discovered something unusual about the star.

The researchers discovered that the star's luminosity occasionally dipped by 20 percent, and its brightness seems to follow a downward trend throughout the observational period.

For the first few years, Tabby's Star dimmed at about 0.34 percent every year. Then in the next 200 days, the star's light level dropped by 2.5 percent. Throughout Kepler's four-year observation period, Tabby's Star dimmed about 3 percent, which astronomers consider a big difference. Looking at other 500 stars in the vicinity, the scientists did not find any other star that has the same dramatic drop in brightness.

"The part that really surprised me was just how rapid and non-linear it was," Montet said in an interview with Gizmodo.

"We spent a long time trying to convince ourselves this wasn't real. We just weren't able to."

Earlier this year, Bradley Schaefer of Louisiana State University discovered that the Tabby's Star's light output was diminishing by 19 percent. However, other astronomers criticized his findings claiming that the dimming was merely a result of flawed data.

"Tabby's star continues to defy easy explanation," Keivan Stassun, one of the astronomers studying the star's light patterns, said in an interview with

"These intriguing new findings suggest that none of the considered phenomena can alone explain the observations. Of course, the star doesn't have to abide by our hope for a single explanation. In the end, figuring out this puzzle may require accounting for a combination of effects."

The Kepler telescope is no longer observing Tabby's Star, but Tabetha Boyajian has won a crowdfunding campaign to observe her namesake star for a year using the Las Cumbres Observatory Global Telescope Network (LCOGT).