A new theory suggests that KIC 8462852, also known as Tabby's Star or the “alien megastructure star”, is fading because it is emitting less light, not because some obstruction is intermittently blocking our view.
Stars at the beginning and end of their lives can vary dramatically in luminosity, but KIC 8462852 is a middle-aged F type star, only slightly larger than the Sun. Such objects have never been seen varying dramatically in their intrinsic brightness over short periods of time. Consequently, when the Kepler Space Telescope picked up major dips in KIC 8462852's brightness, it was assumed to be a consequence of something getting in the way of its light. Theories ranged from huge structures built by aliens to swarms of comets to its passage through galactic gas clouds.
All of these have proven hard to sustain, particularly in the context of subsequent evidence for the long-term decline in KIC 8462852's brightness. A team of physicists at the University of Illinois at Urbana-Champaign argue it is time to take another look at the possibility the changes in brightness are intrinsic to the star, and offer some evidence for why.
A paper in Physical Review Letters notes that, along with the large dips in brightness that made Tabby's Star famous, there are smaller ones. These appear to obey a power law, a pattern where the frequency of events decreases in relationship to the size of the event.
Small events usually happen more frequently than large ones. Where a power law applies, the decreases in frequency are constant for a particular increase in size. Many different power laws exist, but the paper's authors think KIC 8462852 is following the same one as when snow starts to melt before an avalanche, brittle materials are on the verge of breaking, and neurons fire in the brain prior to an episode.
All of these, known as “avalanche statistics”, are seen in physical systems that are close to a phase transition, where something important changes.
Lead author Mohammed Sheikh believes that the existence of established power laws can help astronomers make sense of patterns in the dips in KIC 8462852's brightness. “This gives us an independent way to interpret the events and check consistency with the model,” he said in a statement.
Kepler didn't watch Tabby's star long enough to see many big dips, something various telescopes are working to correct, limiting the sample data. Even if the relationship is confirmed, Sheikh's work does not explain what sort of phase transition is coming or what physical processes might be driving it. The best the authors can suggest is it represents some sort of magnetic transition. Moreover, Sheikh's work does not incorporate, let alone explain, the claimed long-term dimming of KIC 8462852. This has not been measured precisely enough to study in the same way.
Since we have never seen an F type star behave like this, if KIC 8462852 is about to undergo some sort of transition, it will transform our understanding of stellar behavior – assuming we get to witness it. By the standards of a star that is at least several hundred million years old, an imminent transition could still be thousands of years away.