At the Tabby’s Star Poker Game - Who’s Bluffing?

A Report by Andrew Collins

Wednesday, 30 August 2017. This week various new papers have appeared concerning Tabby's Star (KIC 8462852) and individually they have each managed to muddy the waters so much that, in my opinion, the actions of the authors involved can be likened to the actions of card players in a poker game. Their conclusions, based on their own interpretations of available astronomical data, have them edging their bets in a manner that favors their own hand. Their ideas can contradict those of the other players at the table, perhaps helping to obscure the true picture of what’s going on around the star, which lies 1,300 light years away in the constellation of Cygnus.

So who's bluffing, and who's right? No one knows. And yet not one of the players, who are all prominent astronomers and scientists in a position to have their conclusions published in academic journals, have no idea what card they will turn over next as any new evidence from observations of the star could quite simply change everything.

Joshua Simon plays his hand

The biggest player at the table right now is Joshua Simon. His paper deals with the secular or long-term dimming trend of the star. He proposes that Tabby's Star is not fading to black, but is actually on a long-term variability of approximately eight years. Rises in flux recorded in 2006 and 2014, just after the completion of the initial Kepler mission that provided the earliest data on the star, suggest that in 2022 it will start to recover in brightness. This conflicts with what others have to say on the subject, including amateur astronomer Bruce Gary who is daily monitoring the star from his back garden observatory in southern Arizona. He predicts a recovery in the star’s long-term dimming in 2018. In contrast, Fredric Parker, an engineer who posts regular video updates on Youtube, has openly stated that the star's long-term dimming means it will no longer be visible from earth by 2031, and from space telescopes by 2034.

Joshua Simon also dismisses the star's reported rotational period of 0.88 days, citing the work of a team led by Valeri Makarov and Alexey Goldin, who in their own paper published in 2016 concluded that it was most likely interference from a nearby star. This was despite the fact that no star has been determined as the source of this rogue signal recorded in connection with KIC 8462852 during the four-year period of the Kepler mission between 2009 and 2013. What's important here is that Makarov and Goldin needed to dismiss the star's 0.88-day rotational period in order to propose their own theory of what was causing the star's dimming events, for in their opinion their cause is dust and debris between here and the star.

Why exactly did Makarov and Goldin need to dismiss the star's 0.88-day rotational period? The answer is that Dr Tabatha Boyajian and her team in their initial study of the star's strange light fluctuations had found that the time gaps between various of the major and minor dimming events reflected a periodicity of 48.4 days with a half cycle of 24.2 days. Both values were muliples of the star's 0.88-day rotational period (55 stellar rotations in the first instance and 27.5 in the second). This is something that has been investigated by Rodney Hale and myself in our own recent study of the star. We also determined the existence of a base periodicity of 9.68 days, or 11 0.88-day rotational periods.

The existence of such periodicities linked with the star's own rotational period helps argue against the idea that whatever is causing KIC 8462852's short-term dimming events is far away from the star in the interstellar medium. So the presence of the 0.88-day cycle in the Kepler data simply could not be associated with Tabby's Star.

No new evidence is presented by Joshua Simon and his team to confirm the findings of Makarov and Goldin. He simply accepts their findings in this respect.

Simon puts down the star’s long-term dimming to magnetic variability. This might actually be a good call, and could help to explain the star’s apparent periodicities, which are all simply expansions of its stellar rotational period of 0.88 days. I had already considered that they might be linked with powerful magnetic variability in the star, and so will be looking closely at Simon's evidence for the eight-year variability to see how exactly this fits into the gradually emerging picture.

Space Dust

A separate paper by Huan Meng and his team including Dr Tabatha Boyajian examines the variability of absorption lines in the star’s color spectra and concludes that its long-term dimming is caused by obscuring dust. Clearly, this contradicts Joshua Simon’s own opinions on the matter. Thus we can see how easy it is to come up with alternative views using available data and evidence.

Another study by Mario Sucerquia et al accredits the short-term dimming events to a large ringed, Saturn-like planet. It is an interesting idea, with some merit, although it ignores the light dips' apparent periodicities, as well as their unique sharpness, and, of course, the long-term dimming, which occam's razor tells us should be related in some manner. Big ringed planets in a tight orbit around the star is certainly the story that has grabbed the most media attention this week, with headlines around the world claiming “Alien megastructure star mystery finally solved.” Hopefully, all the dust (no pun intended) will settle in due course, and we can once again see the wood for the trees in this great mystery of our times.