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

If you’re looking for a guide to this series, click here.

Last time we finished up our roundup of hypotheses for Boyajian’s Star.  Let’s summarize them:

Plausible Hypotheses

  • #3 Small-Scale ISM structure: This will find support if future dimmings are accompanied by increased reddening and sodium absorption.
  • #4 An Intervening Bok globule: In addition to the above, this would be supported if we discover a cloud of neutral gas near Boyajian’s Star.
  • #7 Comets and other circumstellar material: Plausible for the dips. Would be supported if future dips are accompanied by significant infrared flux and absorption features consistent with cometary or other circumstellar material.

Less Plausible Hypotheses

  • #5 An Intervening Black Hole Disk: Would find support if we can detect the central object or if the dips repeat in reverse order, as with J1407, or if more rigorous analysis shows this to be more likely than we have estimated.

Hypotheses with Unclear Plausibility

  • #2 A Solar System Cloud: Would have plausibility if such a cloud is theoretically realistic, if the cloud were found by other means, or if the dimmings are accompanied by absorption features characteristic of Solar System ices.
  • #9 Alien Megastructures: Would find support if all natural hypotheses are ruled out, we detect signals, or if star suffers significant achromatic extinction.
  • #13 Post-Merger Return to Normal: Would have plausibility if Boyajian’s Star is found by Gaia to be overluminous, and if simulations show this could explain the dips and dimming timescale.

Not Likely Hypotheses

Very Unlikely Hypotheses

And here’s a handy guide for what the Gaia parallax, which will determine the distance to Boyajian’s Star and is due out on September 14, will tell us:

  • 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.

You can vote on what you think Gaia will find here.

The paper is Wright & Sigurdsson, on the arXiv here.  Thanks for reading, and hopefully we’ll know a lot bit more in 11 days!

Update: Jason Curtis points out that the first Gaia release will not actually have the precision to distinguish among these cases!  So unless the parallax comes out really for from 450, we’ll have to wait longer than Sep. 14.

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

  1. dryson


    After looking at the image of the perceived Dyson Sphere I noticed that another light source was reflecting off of the surface of the sphere.

    If a Dyson Sphere was indeed present its enormous surface area would definitely create an unnatural reflection while creating a decrease in light.

    Perhaps the reason why there are several increases in light of KIC 8462852 is that light is reflecting off of the surface of the Dyson Sphere from another sun.

    There are two increases in light on either side of the 15% dip which does seem very unnatural to say the least. Unnatural because the light shouldn’t increase if a planet is transiting across in front of KIC 8462852.
    Perhaps an object that is orbiting KIC 8462 has a metallic shell around it that caused the increase in light due to light from KIC 8462 reflecting on of its surface that the reason for the mirrored increase in light is that the area on the object orbiting KIC 8462, during the 15% dim, revolved on its axis creating the first increase then transited and the same area created the second increase in light as area came back into the same path that the first increase of light was created.

  2. Stan Wright

    From your section 6:

    “At a distance of 10,000 au, the annual motion of the Earth (or Kepler) corresponds to a parallax of 20”. In order to persistently dim Boyajian’s star and explain the secular dimming, the material must span this angle, and so be ~1 au across at that distance. The material’s own orbital velocity is smaller by $\sim 1/\sqrt{a}$ or ~100 at that distance, consistent with the effects being observable for 100 years. Material closer than this distance must span a proportionally larger space to persist on annual and century timescales. Material much farther than 100,000 au should be considered interstellar (see Section 7).”

    I woke up early this morning thinking of this effect, and wondered if performing a long duration exposure of the immediate area around KIC 8462852 would be able to reveal or at least constrain the size of a molecular cloud in orbit around the star, or in interstellar space. Background galaxies should demonstrate near to complete extinction in identifiable regions of the exposure field if there is anything in the ISM or solar system out to specific size vs. range constraints.

    2 arcseconds to the possible KIC8462852 M class companion star is only around 900 a.u.. If the object(s) responsible for the obscuring effect are out to 10,000, that would be around 20 arcseconds, and 100,000 au would be 200 arcseconds. The Hubble ultra deep field exposures ( HUDF) of were 2.4 arcminutes edge to edge, so this is a possibly useful experiment to look for larger structure in the ISM but probably not accurate enough for material within closer orbits that span just a few hundred a.u in size.

    The HUDF exposures reveal thousands of objects within the 2.4 arcminute field, so this would be comparable to having thousand of background objects within the field of view out to 100,000 a.u to measure for hypothetical statistical extinction density of the background objects.

    * this was also posted on the NSF website, where I linked to your papers

  3. Dryson

    Cygnus X-I and the nearby Black Hole

    Is the black hole near Cygnus X-I in between a clear line of sight when Kepler looks at KIC 8462852? If so is some of the light traveling from KIC 8462852 not making it past the black hole which could explain the decrease in the light of KIC 8462.

  4. Dryson

    I was reading the article about a planet that was discovered orbiting two Red Dwarf stars.


    In binary-star systems, the two stars orbit a common center of mass. When one star passes in front of the other from our perspective on Earth, gravity from the closer star bends and magnifies the light coming from the star in the background. Astronomers can study this distorted light to find clues about the star in the foreground and any potential planets orbiting the star system.

    Perhaps there is a new phenom taking place that instead of two stars being close together where the closer star bends and magnifies the light maybe two stars far apart with the star closer to us causes the light behind the main star to bend and reduce the magnification causing the light curve of the second star to dim dramatically.

    For every action there is an equal and opposite reaction. The equal and opposite reaction of the process discussed in the article would be that one star would have a dimmer light curve.

  5. Dryson

    http://www.sciencealert.com/researchers-just-found-a-second-dyson-sphere-star – EPIC 916

    Two stars experiencing dramatic light curves.

    I think that by connecting KIC 8462 and EPIC 916 together in a three dimensional computer animation with a line and then map how the line between the two stars fluctuates, twists, curves, ebbs, etc. as both stars move through space. We might have a better understanding of what is taking place with both stars and possibly between both stars as the fluctuations in the line curving and twisting between both stars might unveil hidden interactions paralleling the line fluctuations as both stars complete their movements through space.

  6. Dryson

    http://www.sciencealert.com/researchers-just-found-a-second-dyson-sphere-star – EPIC 916

    Two stars experiencing dramatic light curves.

    I think that by connecting KIC 8462 and EPIC 916 together in a three dimensional computer animation with a line and then map how the line between the two stars fluctuates, twists, curves, ebbs, etc. as both stars move through space that we would have a better understanding of what is taking place with both stars and possibly between both stars as the fluctuations in the light curves of both stars might unveil hidden interactions paralleling the line fluctuations as both stars complete their movements through space.

  7. Martin

    Here’s another solution not mentioned. Here follows my ask paper about it.
    PS. I queried GAIA for the parallax of Boyajian’s star. The answer came out at 391 pc so we are back to megastructures? Bear in mind that my expertise in this area isn’t great.
    PPS. I propose that this star be named Tabetha Boyajian, so all current names will be valid. WTF Star doesn’t look good in papers, so sorry Tabby!

    A biological hypothesis to explain Boyajian’s star

    KIC 8462852 has once more flummoxed many with dimming on possibly three levels: perhaps gradually by the century, both gradually and steeply over 4 years, with the steep phase over 6 months, and the 2-3 days aperiodic massive transit events which initially brought it to wider attention, and which, perplexingly, appear to have no relationship with the gradual dimming observed in the same period.

    Nearly every theory proposed finds it hard to satisfy all three observations, assuming that the 100-year dimming is real, as seems more likely now, on the assumption that a single phenomenon is responsible.

    The system’s lack of an infrared excess precludes many explanations, incuding alien megastructures. These must also re-radiate their sun’s energy as IR by the laws of thermodynamics.

    What might be the true significance of the SETI search with a null result at KIC 8462852?

    The SETI team calculated the minimum strength of a potential extraterrestrial radio transmitter producing a signal detectable on Earth. This turned out to be larger than the Earth’s current best effort at Arecibo, but could be assumed to the capability of a Dyson Sphere-builder.

    The SETI team also specifically looked at frequencies and bandwidths likely as background radiation coming from a propulsion system. In both cases, the null result matches with the lack of IR excess, making it more likely that there are no megastructures.

    Finally, there is the point that a technological civilization might be aware of its odd light curve from the view of other stars, which would make some kind of omnidirectional beacon more likely, but this has not been discovered either.

    With both physical and technological explanations failling, perhaps a third explanation in betweeen the two might be proposed, which might be a purely biological phenomenon and not indicative of intelligence beyond the hive mind of a superorganism.

    One can only guess at a theoretical substrate for an organism that could block the light from a star in the middle of space on such a massive scale, perhaps some aggregation of rocks/dust and liquid water where simple life could evolve or be seeded from elsewhere, if its chemistry was like Earth’s life. Certainly this is the weakest part of such a proposal. On Earth, the nearest analogues for such a life form might be blooms of algae or phytoplankton, which can grow to many thousands of kilometres long.

    However, once granted, it might explain all three levels of dimming and the lack of IR excess. An organism, or a colony of organisms, could grow over centuries in exponential progression, or grow in effects seen over 4 years. The transits could be done by large random chunks of organism. A simple unicellular base organism could evolve in the short timescale of the star’s life. Photosynthesis or an analogous process might fix the star’s radiation energy in food molecules and not re-emit as IR. Finally, such an organism might produce distinctive spectral lines of the gases involved in its energy-fixing process, such as oxygen and CO2 if this was photosynthesis.

    Phytoplankton Bloom off Ireland, June 2, 2006.
    Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Aqua satellite

    I’ll admit that when I told this theory to my sister, she suggested that cosmic kudzu might need a special weedkiller.

  8. Harry R Ray

    One possible solution NOT discussed was a possible extremely large dark-matter core at the center of the star causing strange INTERNAL effects resulting in the unusual flux. Is this idea even DISCUSSED as a possible solution? Oh, and by the way, on the topic of dark matter: The 750 GeV signal is dead, long(?????) live the 270 Gev signal!@

  9. ericSECT

    Perhaps the SINS/Bok globule is fairly stationary and compact, and Tabby’s (very small, very slow) apparent motion across our sky recently moved it into the dust/gas cloud about 100 years ago.

    Someone can crunch numbers, and constrain the size of this thing given star density around Tabby’s and Tabby’s apparent motion.

    For example: “Given, Tabby’s moved one arc second last 100 years but there are other stars within one half arc second of Tabby’s, then the SINS/BOK must be <one half arc second across along the apparent motion vector" etc.

    Once you can size the thing (at least along one axis) you can check if theories allow that size to occur and if so, you can get a handle on how likely this compact SINS/Bok will form. You can move on to probability of detection for other stars (ie: How often do these half-arc-second-across SINS/Boks occur and how likely are they to be observed?) and rule this hypothesis IN or OUT.

    Perhaps this SINS/Bok thingie moves in the same direction as Tabby's apparent motion, and can be even smaller in size.

  10. jtw13 Post author

    Yes, I realize now that my paper leaves out some dynamical circumstellar solutions. There is an existing Spitzer program to look for NIR excess resulting from planetary collisions—the idea is that the NIR could take a while to show up, but should appear over the next few years. Most of my arguments assume steady-state.

  11. Herp McDerp

    Just grasping at straws here …

    What about a variant of Hypothesis 7, circumstellar debris, but in a rare and unlikely form that isn’t a disk? Specifically, a rare and unlikely form that we’re pretty sure actually does occur: the aftermath of a giant impact? The star is young enough (given its spectral type) that planetary orbits might not have stabilized yet. An impact at very high velocity might result in *several* debris swarms rather than one (as in the Earth-Moon system) and might even trigger a cascade of impacts with other planets in the system. And there’s no need to limit this scenario to terrestrial planets; I wonder what you’d get if you crashed a couple of warm Neptunes together at high velocity?

    Heh. You could even modify this into an alien megastructures scenario, if the aliens engage in planet-smashing wars of the sort described in E.E. Smith’s Gray Lensman, Iain Banks’ Consider Phlebas, or Vernor Vinge’s A Fire upon the Deep.

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