Leonard Kelley holds a bachelor's in physics with a minor in mathematics. He loves the academic world and strives to constantly explore it.
KIC 8462852. Otherwise known as Boyajian’s Star or Tabby’s Star (for the discoverer, Tabethya Boyajian), the Kepler designated name doesn’t do this object justice. The intrigue it has garnered is well justified. You see, this star has a dimming pattern that appears rather random and goes on and on as well as more intense than any other star like it (as much as 22%). That is, an F3 main sequence star located 1,300 light years away is acting unlike any previous star seen. In fact, past observations of Tabby’s Star show an overall dimming of 15% over a 100 year span, based off 1,500 images from the Harvard database. Several theories were brought to explain the observations, and boy are some of them are out there (Cartier 38, Timmer). Let’s examine the candidates and find out the most likely cause for this mysterious behavior.
Plenty of stars have active surfaces. This one shouldn’t. F-type stars are in the stable part of their life so they shouldn’t be doing much. Yet observations from January of 2018 indicated that different wavelengths of light were being affected at different times, something an active surface could produce. However, no indications of starspots have been seen in any spectrum readings, plus no known starspot mechanism can produce the dips seen, despite a power law relation witnessed by Mohammed Sheikh and his team at U of I at Urbana Champaign. If Tabby’s Star was a Be type, it could spin so fast that pieces of the surface would fly away, causing dips occasionally. However, this would produce infrared emissions that are not seen (Klesman, Green, Rzetelny, Cartier 39).
While it is unlikely they are directly the cause, the dust that comets produce may be responsible. But something would have to pull in a large number of comets from an Oort cloud-like feature, which would be reasonable if Tabby’s Star had a companion. Follow-up observations of the star did reveal a potential companion star far away enough to perhaps tug and sent comets into the system. But it’s a bunch of hypotheticals rolled up into one, so unlikely to be the case. Plus, comets heat up as they approach their star and thus should heat up enough to be spotted in the dip. This is not the case, as IR readings have shown (Plait, Rzetelny, Cartier 39).
Okay, plenty of options are available here. It definitely cannot be a big exoplanet, because to block out as much as 22% of the star’s light would require a massive object that has never before been spotted. It could be a small exoplanet’s atmosphere (and surface) being blasted away because of its close proximity to Tabby’s Star. It would look similar to a comet with a tail, but the material itself would be very different, possibly even dust-like. It certainly has happened, but models will be needed to run if any feasibility is to be gathered (Plait, Redd).
Maybe it’s a giant ring system around a planet instead. However, many issues arise with this. First, the rings would have a diameter three times that of Saturn’s rings, something highly unlikely. Second, if the rings were to have the variability we see they would have to wobble in the star’s gravity but that would actually destroy the rings (Shostak).
Advanced by Fernando Ballesteros (University of Valencia) and his team, this idea proposes that a big exoplanet orbits Tabby’s Star and carries with it some Trojan asteroids, caught in gravitational lowlands caused by interactions with the exoplanet and the star. This is not without precedent, for Jupiter and other planets in our own solar system have their own sets like this. And thus, the exoplanet may have a ring system around it as well like Jupiter, further blocking out the light from Tabby’s Star. However, it would have to be a huge planet, almost the size of a red dwarf, which has never been spotted before. Maybe it’s an exoplanet in development, but the host star is too old for such a feature. The big thing about this theory is that it can be tested, for based on the configuration stated scientist can predict some of the next dips. If spotted at the right times, it would be a big plus for confirming this theory (Green).
This is the left-field option, but I will mention it here still. Picture an advanced alien civilization looking to harness more energy to its growth. Where would a better source be than a star? So they build huge platforms in space to gather in the light. This is a Dyson swarm, and it could block out light in a random fashion. To see if aliens are at root here, the SETI Institute employed its Alien Telescope Array, made of 42 antennas, and searched for radio signals that an advanced civilization would produce such as 1 hertz and broadband, not to mention laser communication abilities. Nothing has been seen to indicate that aliens are afoot. Plus, observations from January of 2018 showed those differentiated wavelengths, something that an opaque object like a Dyson swarm couldn’t allow for (Rzetelny, SETI, Cartier 40, Masterson).
This seemed like an easy pick initially, because dust is…everywhere. Seriously, space has tons of it out there, especially around stars courtesy of gravitational interactions. But data didn’t show a strong signal that we are dealing with dust: infrared radiation. This has to do with the wavelength of light that can navigate the distances between dust as well as the light hitting the dust and warming it up, causing infrared rays to be emitted. None of this was spotted with Tabby’s Star (which should be too old for dust anyway), and instead was rather quiet in that portion of the spectrum. But the expected lack of UV rays was spotted, indicating more of them were dimmed than infrared (Klesman, Berger, Wenz, Cartier 39).
January of 2018 would see this issue tackled and bring dust as the major candidate for the observations seen. The key was four major dips in 2017, recorded from start to end in several telescopes. Scientists noticed that different wavelength of light were affected, with blue dipping the most and red the least, something that a huge solid object like an alien superstructure wouldn’t do. No, this would be caused by a bunch of tiny, tiny objects or perhaps by surface flaring. The type of dust could explain the lack of infrared intensity seen, with the size of the individual grains narrowed down to around a micron. But what could be making the dust? Maybe it’s not around the star but between us and it, like in the interstellar medium. Evidence from Valeri Makarov shows stars near Tabby’s Star seem to have more dips than are normal. Maybe there is something to this after all (Klesman, Plait, Cartier 39).
More Out There?
It would help tremendously if scientists had a larger sample size to examine for some further clues. With this in mind, Edward Schmidt (University of Nebraska, Lincoln) used an algorithm searching for similar patterns in the All Sky Automated Survey for Supernovae while eliminating any results that could be explained with typical binary scenarios. In total, 21 hits were found, and further analysis indicated two populations. 15 are considered to be like Tabby's Star and are thus called slow dippers. The remaining 6 have much higher variability to their light curves and are thus called rapid dippers. Looking at their positions on the H-R diagram points to dippers overall being main-sequence stars of about 1 solar mass or are evolved red giant stars of about 2 solar masses. Now that we have more objects to look at, thus giving us more potential answers to the ongoing mystery of Tabby's Star (Kohler).
Berger, Eric. “Dimming of Tabby’s Star Likely Caused By Something Less Sexy Than Aliens.” Arstechnica.com. Conte Nast., 04 Oct. 2017. Web. 24 Jan. 2018.
Cartier, Kimberly and Jason T. Wright. “Strange News from Another Star.” Scientific American May 2017. Print. 38-40.
Green, Alex. “Can We Explain the Curious Case of Tabby’s Star?” skyandtelescope.com. Sky and Telescope Media, 09 Jun. 2017. Web. 23 Jan. 2018.
Klesman, Alison. “Astronomers Are One Step Closer to Unlocking the Mystery of Tabby’s Star.” Astronomy.com. Kalmbach Publishing Co., 04 Jan. 2018. Web. 23 Jan. 2018.
Kohler, Susanna. "Are There More Stars Like Boyajian's Star?" aasnova.org. AAS Nova, 13 Sept. 2019. Web. 18 Oct. 2022.
Masterson, Andrew. "Laser test finds no evidence of alien megastructure around." cosmos.com. Cosmos. Web. 01 Mar. 2019.
Plait, Phil. “Tabby’s Star: Sorry, Folks, But It Really Isn’t Aliens.” Syfy.com. Syfy, 03 Jan. 2018. Web. 23 Jan. 2018.
Redd, Nola Taylor. “’Alien Megastructure’ Star May Be a Sign of a Dying World.” Astronomy.com. Kalmbach Publishing Co., 19 Jul. 2017. Web. 24 Jan. 2018.
Rzetelny, Xaq. “Something – we’re not sure what – is radically dimming a star’s light.” Arstechnica.com. Conte Nast., 16 Oct. 2015. Web. 24 Jan. 2018.
SETI. “Looking for Deliberate Radio Signals From KIC 8462852.” Seti.org. SETI Institute 05 Nov. 2015. Web. 25 Jan. 2018.
Shostak, Seth. “Has Tabby’s Star Mystery Finally Been Solved?” nbcnews.com. NBC Universal, 01 Sept. 2017. Web. 24 Jan. 2018.
Timmer, John. "Star's bizarre optical antics go back at least a century." arstechnica.com. Conte Nast., 19 Jan. 2016. Web. 11 Dec. 2018.
Wenz, John. “Ok, So What’s Really Going on with Tabby’s Star?” astronomy.com. Kalmbach Publishing Co., 13 Oct. 2017. Web. 24 Jan. 2018.
© 2018 Leonard Kelley