The Mystery of Tabby’s Star

Popular interest in Tabby’s Star—also known, less imaginatively, as KIC 8462852—continues as Yale astronomer Tabetha Boyjian just reached her $100,000 fundraising goal to look further into the spectral anomalies of this mysterious object. Tabby’s Star has been on the radar of alien intelligence enthusiasts ever since the discovery of anomalous and substantial (up to 20 percent) drops in its light curve. The drops were irregular and lasted between 5 and 80 days. Why the excitement? Because there’s a small—make that miniscule—chance that the dips in brightness are caused by artificial constructions built by alien civilizations.  

This notion, however, is difficult to support. First, Tabby’s Star is an F-type star nearly 1,500 light years away. Main-sequence F stars are heavier than our Sun, and most have a life expectancy of less than two billion years. Here on Earth, it took more than 4.5 billion years for the first technological species (us!) to appear. Thus, any planet around KIC 8462852 would not be expected to be inhabited by complex or intelligent life.

The question remains, though: What is causing the mysterious dimming? A 20 percent dip in the light curve means that whatever object is blocking the star must be very substantial in size. (A Jupiter-size planet would cause only about a one percent drop in brightness.) The leading hypothesis is that a swarm of comets with an unusual orbit may be responsible, although it’s hard to imagine comets having such a pronounced effect. I was drawn initially to another explanation: that large pieces of planetary debris, for example from a collision, are blocking the light. But no excess of infrared light, which would be expected after such a collision, has been seen, which seems to rule out that possibility.

The preferred explanation among alien intelligence enthusiasts—a Dyson Sphere—also seems to be a non-starter. Dyson spheres are not gravitationally stable, and a so-called “Dyson swarm” of lots of small spacecraft also seems to be unrealistic. The zillions of objects would have to be extremely closely spaced. And why would they only block out light at irregular intervals? SETI searches of Tabby’s star after the initial discovery did not find any evidence of technology-related signals or optical beacons.

Other hypotheses exist, for example that we’re seeing the effects of dark matter or dark energy, about which we know very little. So far, then, we have a list of hypotheses that don’t seem to work, and no good way to explain the observed phenomenon. Perhaps this is why Tabby’s Star drew so much interest (and financial support!) from the public. Thanks to the successful Kickstarter campaign, KIC 8462852 can now be observed continuously by the Las Cumbres Observatory Global Telescope Network—a nice example of how “citizen scientists” and crowdfunding can help figure out a genuine scientific puzzle.

Dirk Schulze-Makuch | | READ MORE

Dirk Schulze-Makuch is a Professor at the Technical University Berlin, Germany, and an Adjunct Professor at Arizona State University and Washington State University. He has published eight books and nearly 200 scientific papers related to astrobiology and planetary habitability. His latest books are The Cosmic Zoo: Complex Life on Many Worlds and the 3rd edition of Life in the Universe: Expectations and Constraints.

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