The mystery continues. Astronomers may have to think just a little bit harder to solve the mystery behind Boyajian's star.

For the uninitiated, Boyaijan's star was discovered by Yale University's Tabetha Boyajian and her team in Septmeber 2015. 

The star, originally named KIC 8462852, has dimmed dramatically over the past seven years - with one time dimming by a surprising 22-percent.NASA's Kepler space telescope spotted this anomaly. However, according to Space.com, the brightness dips of the star were far too significant just to be caused by an orbiting planet. 

Hence the birth of the alien megastructure mystery. 

Space.com says researchers have come up with a variety of alternative causes for the dimming. This includes swarms of broken-apart comet fragments, a variability in the activity of the star, a cloud of some sort in the interstellar medium, and an orbiting "megastructure" built by aliens.

According to Space.com, researchers are testing these hypotheses. For example, there's a $100-million Breakthrough Listen initiative using the Green Bank Telescope in West Virginia to hunt for signals coming from Boyajian's star, which lies about 1,500 light-years from Earth.

According to Space.com, the Green Bank observing run will wrap up next month, according to Jason Wright of the Pennsylvania State University. 

Wright spent the past 15 months pondering what may be happening with the star. He's also the leading author of the recent study outlining the various possibilities. 

The mystery has only deepened since the 2015 discovery. Early last year, astronomer Bradley Schaefer of Louisiana State University determined that in addition to the periodic dips, the star dimmed overall by about 20-percent from 1890 to 1989. This was supported further by another 2016 study, which found out the star dimmed by about 3-percent between 2009 and 2013.

Wright said the most likely explanation is interstellar-cloud explanation, but he's not betting on it. Researchers may have to dig a bit deeper to find out what is really happening to Boyaijan's star.