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Comet storm, not alien megastructures
This illustration shows a star behind a shattered comet. (Credit: NASA / JPL-Caltech)

That mysterious “alien megastructure” star is still a mystery, but the most plausible explanations appear to be dense patches of interstellar gas or dust that just happened to pass in front of the star.

That’s the upshot of analyses conducted by the astronomer who first raised the idea of an extraterrestrial construction project a year ago.

In the Astrophysical Journal Letters, Penn State’s Jason Wright and a co-author, Steinn Sigurdsson, run through a wide range of hypotheses for the behavior of a star called KIC 8462852, also known as Boyajian’s Star or Tabby’s Star.

Not even the alien hypothesis is ignored.

The mystery has to do with a strange pattern of erratic dimming and brightening that was observed by NASA’s Kepler space telescope. That pattern was noted last September in a study with Yale astronomer Tabetha Boyajian as principal author. (Hence the star’s nickname.)


Wright suggested that the dimming could theoretically be caused by shifts in an alien megastructure surrounding the star – perhaps a giant energy-generating Dyson sphere built by an advanced civilization.

Later studies reported that the star, which is located 1,500 light-years from Earth in the constellation Cygnus, had undergone other long-term dips in brightness.

Is it aliens? Wright says the idea is “not completely ruled out, yet” but “very unlikely.” In their latest study, Wright and Sigurdsson say stellar observations from the European Space Agency’s Gaia satellite could definitively rule out the alien hypothesis or keep it alive.

Many other explanations have been proposed for the observations of Boyajian’s Star, including variability in the star, or swarms of comets passing in front of it. But Wright and Sigurdsson favor a scenario in which small-scale density variations crop up in the interstellar medium between us and the star.

Those types of variations – for example, short-lived patches of gas and dust, or small molecular clouds – would have to be rare. “But it turns out rare dense patches are a thing!” Wright says.

Future observations, either of repeated dimming patterns at Boyajian’s Star or of similar dimming by other stars, would lend additional support to this hypothesis. The comet swarm hypothesis is also still in the running, plausibility-wise.

For what it’s worth, there’s talk about even more dramatic patterns of irregular dimming that have been observed in a star called EPIC 204278916.

The observations from Kepler’s K2 mission were reported in a paper published last month in the Monthly Notices of the Royal Astronomical Society. The study could bring additional perspective to the debate over Boyajian’s Star.

To get the rundown on the full range of hypotheses for Boyajian’s Star, including black holes, check out the research paper as well as the AAS Nova update and Wright’s analysis on his AstroWright blog.

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