Spurred by a controversial claim that the star’s brightness gradually decreased by 14 percent from 1890 to 1989, Montet and Simon decided to investigate its behavior in a series of Kepler calibration images that had not previously been used for scientific measurements. “We thought that these data could confirm or refute the star’s long-term fading, and hopefully clarify what was causing the extraordinary dimming events observed in KIC 8462852,” explained Simon.
Simon and Montet found that, over the first three years of the Kepler mission, KIC 8462852 dimmed by almost 1 percent. Its brightness then dropped by an extraordinary 2 percent over just six months, remaining at about that level for the final six months of the mission. The pair then compared this with more than 500 similar stars observed by Kepler and found thata small fraction of them showed fading similar to that seen in KIC 8462852 over the first three years of Kepler images. However, none exhibited such a dramatic dimming in just six months, or a total change in brightness of 3 percent.
“The steady brightness change in KIC 8462852 is pretty astounding,” said Montet. “Our highly accurate measurements over four years demonstrate that the star really is getting fainter with time. It is unprecedented for this type of star to slowly fade for years, and we don’t see anything else like it in the Kepler data.”
At the moment, there is no good theory based on what astronomers know of stellar evolution to explain this star's behavior. This does not mean the only explanation left is that aliens are building a Dyson sphere around the star, but it also leaves everyone at a loss to explain what is happening.
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