Universe Today
KIC 8462852 (aka.
Tabby's Star
) captured the world's attention back in
September of 2015
when it was found to be experiencing a mysterious drop in brightness. A week ago (on
May 18th
), it was announced that the star was at it again, which prompted observatories from all around the world to train their telescopes on the star so they could observe the dimming as it happened.
And just like before, this mysterious behavior has fueled speculation as to what could be causing it. Previously, ideas ranged from
transiting comets
and a
consumed planet
to
alien megastructures
. But with the latest studies to be produced on the subject, the light curve of the star has been respectively attributed to the presence of
a debris disk and Trojan asteroids
in the system and a
ring system
in the outer Solar System.
The first study, titled "
KIC 8462852: Will the Trojans return in 2021?
", was written by a team from the
University of Valencia
, the
Institute of Physics of Cantabria
(IFCA) and the
Astrophysical Institute of Andalusia
(IAA). The paper was recently submitted to the
Monthly Notices of the Royal Astronomical Society,
and presents the argument that the dimming of Tabby's Star can be explained by the presence of stable debris.
[caption id="attachment_135720" align="aligncenter" width="580"]
Diagram of the KIC 8462852 system, showing the possible influence of Trojans on its brightness. Credit: F. Ballesteros et al.
[/caption]
Led by Fernando J. Ballesteros, the team used data obtained by the
Kepler mission
to create a model of the system that could account for all the dips in brightness. These include the up to 20% drop that was observed in 2015 and the non-periodic repetitions and asymmetric dips that followed. From this, they determined that a ringed body and Trojan asteroids that share its orbit could explain the first large dip and the subsequent period of dips.
This explanation not only offers an entirely natural account of what could be causing the star to dim, but also offers a prediction that (if true) would confirm their theory. As they state in their paper:
Interestingly, Jason Wright - an associate professor from Penn State University and the one who proposed the alien megastructure theory - chimed in on this paper. And it only seems fair, since the team refer to his work in their study! As he indicated on his website,
AstroWright
, the theory does have several strong points, but does not account for certain observations.
[caption id="attachment_131689" align="aligncenter" width="580"]
Artist's impression of an orbiting swarm of dusty comet fragments around Tabby's Star. Credit: NASA/JPL-Caltech
[/caption]
As he states, the dips observed from Tabby's Star are quite steep, which is something natural phenomena cannot easily account for. Their study also does not address things like secular dimming, or the upper limits of IR and millimeter wave-observations. But perhaps most glaring, according to Wright, is the mass that would be required to create the kind of dimming that has been seen:
The second paper, titled "Tabetha's Rings", was also recently submitted to
MNRAS
. Written by Professor Jonathon Katz of the Department of Physics and
McDonnell Center for the Space Sciences
at Washington University, the paper argues that the dips observed from Tabby's Star could be caused by matter in the Solar System - specifically, a ringed object that lies between Kepler's line of sight and KIC 8462852.
Based on the interval between dips, and the orbit and line of sight of the Kepler mission, Katz calculated what the distance of this possible ring would be, and provides estimates on the size and distribution of particulate matter within it as well. As he wrote in his study, a 600 m large object would be able to obscure all light coming from the Tabby's Star, although only briefly.
[caption id="attachment_132953" align="aligncenter" width="580"]
Could a ring-like structure in the outer Solar System be what's causing the observed dimming of Tabby's Star? Credits: NASA/JHUAPL/SwRI
[/caption]
What's more, given the orbital motion of Kepler (and the Earth), the observed dips in brightness would require the existence of an obscuring cloud that extends along the ring a distance equal to the distance the telescope travels. Ultimately, this paper is more of a thought experiment than a definitive hypothesis, one which Katz acknowledges in his conclusions.
"The occurrence of deep dips in two epochs separated by about two Kepler-years is a hint that the phenomenon may be local rather than circumstellar," he states. "This evidence is suggestive but not statistically compelling because the interval differs from an exact integer multiple of Kepler-years by a few percent. However, the difficulty of developing a compelling circumstellar model and the history of discovery of narrow planetary rings by stellar occultation justify investigation of possible explanations involving Solar System rings."
Another interesting aspect of Katz's study is the fact that it too makes predictions about future dimming events. In short, his hypothesis indicates that future dips may be observed from Earth at intervals that are just a year apart. But according to Wright, who
commented
on this paper as well, this seems like a miscalculation.
"Some of the implications are worked out, but some of the math seems wrong to me (he predicts that the dips will be visible every 365.25 days from earth, which ignores the orbital motion of that object)," he wrote. However, Wright also congratulates Katz for making this argument since it is similar to one he himself made a year ago (which Katz acknowledged in his paper).
[caption id="attachment_104920" align="aligncenter" width="580"]
Could this be what's causing Tabby's Star to experience drops in brightness, an alien megastructure? Credit: Eburacum45
[/caption]
Last summer (
August 31st, 2016
), when writing on the subject of what could be causing Tabby's Stars observed dips in brightness, Wright considered the possibility that a Solar System Cloud might be responsible:
However, Wright also pointed out the flaws in this theory, stating that such a ring could not account for all the observations made of Tabby's Star, and that he and other astronomers were at a loss to explain how such a ring could have been caused. "Not only is Boyajian's Star
way
above the ecliptic (but does that even matter at 10,000 AU?), but a 20" cloud at 10,000 AU would be 1 AU across. What could cause it?" he wrote.
In the end, we may never know what is behind KIC 8462852's strange behavior. But our ongoing efforts to gather additional information are making increasingly educated guesses possible. As we eliminate more and more in the way of possibilities, we are getting closer to an explanation that actually fits.
Next generation telescopes will certainly help in this regard. And who knows? Someday we may actually be able to explore this system directly and see if any our theories were correct!
Further Reading: AstroWright, MNRAS, (2)