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Will the eventual consensus explanation of star KIC 8462852 variability be an intervening molecular cloud?

This star (aka "Tabby's Star) has been puzzling us for a few years now. Its highly variable apparent magnitude doesn't fit the pattern for other variable stars or stars with eclipsing companions or transiting exoplanets. To date, the dips in brightness do not exhibit any periodicity at all. Even worse, the dips in the luminosity graphs are asymmetrical (gradual onset, sudden reset). For lots of background and prior Metaculus discussion, see this question and this one..

Most attention has been aimed at eclipsing objects orbiting the star itself, and our prior questions had rather short time horizons.

Now I put forward my own pet theory as a binary question with open-ended close: Until such time as the scientific community does a face-palm and says "yeah, of course that's what it was!", is the explanation some passing interstellar gas and/or dust?

From this paper here's a good summary of the molecular cloud conjecture:

7.2. An intervening molecular cloud

Alternatively, there might be a chance alignment with a localized molecular cloud (as opposed to an overdense filament or sheet).

The Clemens & Barvainis (1988) catalog of small molecular clouds was selected optically based on examination of the POSS plates, and was sensitive to clouds smaller than 10′, typically down to ∼1′. Clemens et al. (1991) found that the mean radius of these clouds was 0.35 pc. The clouds in this catalog cluster near the Galactic plane presumably both because clouds are intrinsically more common there and because they are easier to identify in silhouette against the large number of stars there.

A quiescent Bok globule 0.1 pc ≈20,000 au across and midway between Earth and Boyajian’s Star would have almost certainly escaped detection. It would have a radius of 40", and examination of the POSS plates for Boyajian’s Star confirms that the star counts are too low in this region to clearly reveal such a small object, especially if some of the stars in the image were foreground to it and the globule were not spherical. Such high-latitude clouds exist: Getman et al. (2008) describe the "mysterious” high Galactic latitude cloud CG12, which sits 200 pc above the plane at a distance of 550 pc (about the same distance as Boyajian’s Star).

In this case, the secular dimming would be naturally explained by the changing line of sight to Boyajian’s Star through the cloud’s slowly varying radial column density profile,and the dips would then be explained by small-scale (sub-au) structure within the cloud.

This question resolves when a consensus is achieved, and it will retroactively close one year prior to the resolution date. From the earlier questions about this star's consensus explanation:

We'll use the following criteria to specify consensus. Let N be the number of refereed published journal papers that:

  • provide an explanation for the aperiodic dips seen in KIC 8462852, and

  • are cited by at least one published paper, or two preprints, supporting their explanation with additional analysis and/or data, and

  • are cited at least 5 times in total, and

  • are not cited by a published, refereed paper refuting or disputing the given explanation within a year following publication.

If N=1 we will consider a consensus to have been reached. If N>1, and if all of the explanations are qualitatively the same, i.e. involving the same essential physics and objects (e.g. "Comet breakup"), we will also consider consensus to have been reached. Otherwise, we will consider that consensus has not yet been reached.

Resolution will then be positive if an intervening, galactic molecular cloud / gas cloud / supernova remnant is the explanation. Resolution will be negative if the explanation is anything other than interstellar gas and dust in our line of sight (e.g. anything orbiting the star, or the star's intrinsic variability etc)


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