Last October, researchers with the Kepler Planet Hunters program announced the discovery of unusual patterns in the light output of a star indexed as KIC 8462852, patterns that could only be explained by massive objects in orbit around the star, blocking a significant portion of its light. While many theories were put forward to explain the phenomenon, ranging from proto-planetary debris to massive comets, all of the explanations failed to fit what was being observed — except for the otherwise controversial idea that the light might be blocked by massive alien artifacts.

This week, Louisiana State University astronomer Bradley Schaefer published a paper on his research into historical observations of KIC 8462852, now called "Tabby’s Star", named after the astronomer that first studied the star’s odd behavior. Schaefer studied observations of the star made at Harvard University between 1890 and 1989, and found that, in addition to the star’s irregular flickering, it has dimmed by about 20 percent over the century.

This, in-of-itself, is odd: Tabby’s Star is a run-of-the-mill F3 main sequence star, much like our Sun, and so should be stable in it’s output: “The KIC8462852 light curve from 1890 to 1989 shows a highly significant secular trend in fading over 100 years, with this being completely unprecedented for any F-type main sequence star,” Schaefer explains. “Such stars should be very stable in brightness, with evolution making for changes only on time scales of many millions of years.”

Schaefer feels that the century-long dimming phenomenon and the star’s short-term periodic dimming are linked by the same unknown mechanism. He rules out the idea that the light might be blocked by swarms of objects such as giant comets, as by his calculations, the sheer number of objects needed to produce this effect is extremely improbable, at over 648,000 objects.

“I do not see how it is possible for something like 648,000 giant-comets to exist around one star, nor to have their orbits orchestrated so as to all pass in front of the star within the last century,” he concludes. “So I take this century-long dimming as a strong argument against the comet-family hypothesis to explain the Kepler dips."