SAN FRANCISCO Astronomers may have to think a little harder to solve the mystery of Boyajian’s star.

In September 2015, Yale University’s Tabetha Boyajian and her colleagues reported that the star KIC 8462852 has dimmed dramatically multiple times over the past seven years, once by an astounding 22 percent.

NASA’s planet-hunting Kepler space telescope spotted these dimming events. But the brightness dips of “Boyajian’s star,” as it has come to be known, were far too significant to be caused by an orbiting planet, so astronomers began thinking of alternative explanations. [13 Ways to Hunt Intelligent Alien Life]

Researchers have come up with many possible causes for the dimming, including a swarm of broken-apart comet fragments, variability in the activity of the star itself, a cloud of some sort in the interstellar medium between Kepler and Boyajian’s star, and, most famously, an orbiting “megastructure” built by an alien civilization to collect stellar energy.