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The ‘alien megastructure’ star continues to defy explanation

The star KIC 8462852 sits 1,480 light years away in the constellation Cygnus. It’s an unassuming object at first glance, but it became a hot topic in astronomy last year when data from the planet-hunting Kepler telescope showed something causing fluctuations in the light coming from KIC 8462852 (nicknamed Tabby’s Star, after the astronomer who led the original team). It wasn’t a planet, and some speculated that what we were seeing was evidence of a massive alien megastructure.

As much as scientists have tried to come up with a more plausible cause, Tabby’s Star continues to defy explanation. A new report now confirms that in addition to fluctuating, Tabby’s Star has been getting dimmer overall. It’s as if the star is slowly being enveloped.

What originally grabbed the attention of astronomers was the size and duration of the dips in light output. Kepler tries to detect new exoplanets via the transit method. It simply watches for small dips in luminosity when a planet passes in front of its host star. These dips are tiny — usually less than a percent and last only a few hours. The first dip detected from KIC 8462852 blocked nearly 1% of its light (like a large gas giant), but it lasted more than a week. That was just the beginning, though. Kepler detected more drops in light output from Tabby’s Star as large as 20%, which is huge.

The latest data point comes from Caltech astronomer Ben Montet and Joshua Simon from the Carnegie Institute. The pair conducted an exhaustive photometric analysis of the data collected by Kepler during its four years of observing KIC 8462852 and other stars in that area of the sky. They found that, yes, the huge dips that astronomers have been puzzling over are there in the original data. More importantly, its total light output has been dropping over time at a non-linear rate.

light graph

For the first 100 days of Kepler’s observation, Tabby’s Star was losing 0.34% brightness annually. In the 200 days following that, it dropped by 2% before leveling off. A total drop of 3% (in addition to the transit-like drops of up to 20%) is incredibly bizarre. A few months ago, astronomer Bradley Schaefer of Louisiana State University claimed that an examination of old photographic plates of Tabby’s Star indicated that its brightness had dropped by almost 20% in the last century. Other scientists were skeptical of this claim, but now we have some corroboration that Tabby’s Star is indeed getting dimmer overall. Montet and Simon even looked at 500 stars in the vicinity of KIC 8462852 to confirm that none of them was behaving in a similar way.

What we have here is a genuine astronomical mystery. We just don’t know what’s going on in orbit of Tabby’s Star. None of the natural mechanisms scientists have presented can completely explain the data. If this sounds like something out of science fiction, that’s because it is. The idea of a massive structure encasing a star has been around for decades — it’s known as a Dyson Sphere. In fact, astronomical observations very similar to what we see at KIC 8462852 are described in a number of sci-fi novels (Pandora’s Star comes to mind). Maybe this is life imitating art.

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