The mystery surrounding Tabby’s Star just ratched up another notch. Or down, considering the data outlined in Benjamin Montet and Joshua Simon’s latest submission to the arXiv, “KIC 8462852 Faded Throughout The Kepler Mission“. Everyone’s favorite “megastructure” star continues to confound mainstream astronomers and the taboo of last resort, aliens, is still on the table.

Montet and Simon discovered KIC 8462852, a.k.a. Tabby’s Star, dimmed by 2.5% over the course of Kepler’s mission to survey the heavens for alien planets. The data lends support to Bradley Schafer’s conclusion [1] that Tabby’s Star steadily dimmed from 1890 to 1989. What everyone and their telescope are getting excited about is the rate of dimming has been increasing according to the Kepler data.

If the rate of dimming increases, this could be the product of self-replicating machines or von Neumann devices tasked to build this putative alien megastructure. When I looked at Montet and Simon’s graphs, I had an insight on how they could suggest the possibility of self-replicating machines or aliens. Rather than charting the curve of the dimming light, but the ‘growth’ of material or machines causing the dimming, the a graph would show a sigmoid curve. In biology, sigmoid curves illustrate population growth [2, 3] through three phases of transitional and exponential growth before reaching a plateau. In this context transitional growth may be the dust of “construction crews” tearing apart an object for raw materials, followed by exponential growth as another segment of the megastructure is created, before plateauing as the ‘bots travel to the next planetary or cometary resource a mere handful of astronomical units away.

The prospect of aliens, despite my speculation, remains unfalsifiable for now. But Montet and Simon do a handy job outlining the unlikely natural explanations most sane scientists would embrace. Astronomers have observed polar star spots on F-type stars like KIC 8462852, but those F-type stars are cooler and smaller in contrast. Also polar spots can’t explain the short-term dips previously observed by Tabetha Boyajian, et al.. Some of the proposed transit events under suspicion for the star’s dimming are even less likely.

For an optically thick transiting object, the 2.5% transit depth indicates a minimum radius of 0.15R * (Boyajian et al. 2016 estimate a radius of 1.58 R ☉ for KIC 8462852). If the transiting body is in a Keplerian orbit, the extremely slow ingress time and long transit duration place it at the implausibly large distance of ~10 PC, with a transit possibility of ~10-9.

Fingers are crossed that the Tabby’s Star observing campaign with the Las Cumbres Observatory Global Telescope Network, currently underway after the successful Kickstarter, will capture one of the mysterious long transits. Should the cause is a solid object, like a megastructure, then the dimming of KIC 8462852’s light would be achromatic. On the other hand if the culprit is dust and/or gas, then the starlight would redden.

Maybe in a year we’ll know for certain if the alien hypothesis is still worth consideration. Perhaps some science fiction-types will find inspiration around Tabby’s Star for another big dumb object to fit the mystery. In either case, our interesting times are becoming more interesting by the moment.

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