10-part overview of enigmatic ‘alien megastructure’ star, by Jason Wright

Whatever is causing the weird dimming around the star isn't known yet, but theories have ranged from comets to "alien megastructures." Image Credit: NASA/JPL-Caltech
Whatever is causing the weird dimming around the star isn’t known yet, but theories have ranged from comets or dust to “alien megastructures.” Image Credit: NASA/JPL-Caltech

This is a great 10-part overview of Boyajian’s Star (Tabby’s Star/KIC 8462852) by astronomer and astrophysicist Jason Wright, outlining the various hypotheses to date to explain this weird star observed by the Kepler Space Telescope. Whatever is causing the unusual short-term and long-term dimming is still unknown.

What Could Be Going on with Boyajian’s Star? Part I

What Could Be Going on with Boyajian’s Star? Part II: Long-Wavelength Constraints

What Could Be Going on with Boyajian’s Star? Part III: Periodic(?) Dips and Interstellar(?) Sodium

What Could Be Going on with Boyajian’s Star? Part IV: Nearby Stars, Instrumental Effects, and a Solar System Cloud

What Could Be Going on with Boyajian’s Star? Part V: The Interstellar Medium

What Could Be Going on with Boyajian’s Star? Part VI: Black Holes!

What Could Be Going on with Boyajian’s Star? Part VII: Circumstellar Dust

What Could Be Going on with Boyajian’s Star? Part VIII: Alien Megastrutures

What Could Be Going on with Boyajian’s Star? Part IX: Intrinsic Variations

What Could Be Going on with Boyajian’s Star? Part X: Wrapup and Gaia’s Promise

The star is often referred to as Tabby’s Star, nicknamed after Dr. Tabetha Boyajian, who first announced the discovery of the weird characteristics of this star in a paper called Where’s the Flux?. Wright now calls it Boyajian’s Star, to follow the long tradition of using peoples’ last names when naming a new discovery.

An “alien megastructure” such as a Dyson Sphere is one of the more “out there” (and popular) ideas, but so far hasn’t been discounted yet.

The upcoming data release from the Gaia spacecraft on September 14 will hopefully help to narrow down these possibilities, by determining exactly how far away the star is. As Wright explained:

  • “Within 400pc: Means that ISM extinction cannot explain current level of dimming, so favors non-ISM and non-dust explanations. These are #9 ,11, and 12. Could also imply that the cause is very opaque dust blocking part of the stellar disk, so #5, 6, 7, and 8 might still be OK
  • Around 450pc: Means that all of the secular dimming can explained by the dust we observe along the line of sight. Favors #2, 3, 4, 5, 6, 7, and 8.
  • Beyond 500pc: Means that the star is more luminous than we expected from the reddening. Favors #13: return to normal brightness.
  • No answer: Star does not have a good astrometric solution. Unclear how this could happen given the lack of RV variation, but could that the 2″ companion is much bluer than we think, which would be annoying and not tell us very much except that it’s not an M dwarf, maybe boosting #5 (if it’s really the central black hole). Might imply that there is another star nearby that we haven’t accounted for, suggesting new hypotheses.
Artist's conception of one form of Dyson Sphere, a Dyson Swarm. Image Credit: Wikimedia Commons/Vedexent
Artist’s conception of one form of Dyson Sphere, a Dyson Swarm. Image Credit: Wikimedia Commons/Vedexent

There was also this recent new article which postulates that another “similar” star might solve the mystery. However, as Wright points out, there are distinct differences. The second star is a young “dipper” star, and its behaviour is already well known and fairly common:

“There are ‘dipper’ stars that have superficially similar light curves to Boyajian’s Star. But these as caused by close-in disks and other circumstellar debris that are revealed by their long-wavelength emission, which Boyajian’s Star lacks. That was the original reason Boyajian’s Star stood out as being so weird: it’s not young, it has no disk, so it’s not a dipper. I don’t understand why this one keeps coming up.”

All of the “regular” natural explanations have fallen short so far, so while a (necessarily) more bizarre natural explanation is seemingly most likely, the “alien megastructure” hypothesis has also not been discounted yet, as the observations do seem to fit some of the predictions made for how such a thing should be detectable. Only further observations, such as those by Gaia, will help to narrow down the possibilities.

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