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Tabby's Star Gets Even More Mysterious


Tabby's star in Infrared and ultraviolet light. NASA Image

Tabby's star in Infrared and ultraviolet light. NASA Image

What the heck is going on around Tabby's star?

If you follow such things, you'll remember when KIC 8462852, or Tabby’s star -- named after the woman who discovered it, Tabitha Boyajian -- first exploded onto the nerdscape in October of 2015. That's when scientists scouring through data from NASA's Kepler Mission first noticed its weird behavior.

That star sure is weird

The Kepler mission "is specifically designed to survey our region of the Milky Way galaxy to discover hundreds of Earth-size and smaller planets in or near the habitable zone and determine the fraction of the hundreds of billions of stars in our galaxy that might have such planets."

It does it by measuring the light from far away stars, and noting as planets pass between the star and the Kepler photometer. So far, Kepler has discovered more than 2,700 stars that have planet candidates in their orbit, and it's just getting started.

But while one group of scientists was digging through the Kepler data, they discovered an anomaly: Tabby's star — 1,480 light years away in the constellation Cygnus — was not behaving at all like a star its size and age, but instead, was dimmer than it should be and also periodically flickering.

Those findings were published last October at the online site "arXiv" in an articled called "Planet Hunters X. KIC 8462852 – Where’s the flux?". The basic premise was: "We've noticed this happening, but we don't really have any idea why."

The team suggested a few of the most likely "whys" in that original paper.

"We presented an extensive set of scenarios to explain the occurrence of the dips," they wrote, "most of which are unsuccessful in explaining the observations in their entirety. However, of the various considered, we find that the break-up of a exocomet provides the most compelling explanation."

The article called for a lot more study and observation of Tabby's star so astronomers could unravel the mystery. Science scratched its head, said "that's a good idea" and agreed to take a closer look.

That would have been that, except for the fact that we humans are what we are.

Predictably, the web reacted in the same way as creationists trying to get intelligent design into public schools: "We don't know what it is" the web screamed, "IT MUST BE ALIENS!"

Whoa, Tex!

But none of the scientific studies so far mention the possibility of aliens, or extraterrestrial civilizations. But that hasn't stopped sites like Sky and Telescope, and SETI (Search for ExtraTerrestrial Intelligence) Institute from at least entertaining the idea that it was an artificial construct.

It's fun to think about, but — buzz kill that science is — the answer to this puzzle isn't likely to be a Dyson sphere. Unfortunately, knowing what it isn't doesn't do us much good and, since the original article, there has been just a trickle of research about KIC 8462852. The most important advance on the story came out in November and threw big shade at the exocomet theory.

Okay, that star is REALLY weird

Last week, a new paper on Tabby's star came out and a new set of astronomers found new weirdness and came to the unsettling conclusion that "No known or proposed stellar phenomena can fully explain all aspects of the observed light curve."

Say what?

The new research, authored by Caltech astronomer Ben Montet and Joshua Simon of the Carnegie Institute, adds a new layer of questions to Tabby's star.

"There are now three effects observed: the short term flickering from the original paper (Boyajian et al.)," Montet told VOA. "...a long-term dimming over the Kepler mission and possibly for a century, and a rapid decline in the overall flux by 2.5 percent, which wasn't previously observed before." So, Montet says, "Any model that wants to explain the observed light curve now has to explain all three of these." A tall order.

But Montet made this point to VOA: "I want to clarify that this is 'no known or proposed *stellar* phenomena,' meaning phenomena intrinsic to the star itself."

Darn science! That takes a lot of the fun out of the mystery, because Montet is suggesting that the answer is likely to be found between our telescopes and Tabby's star: "some material between us and the star blocking the light," a giant dust cloud perhaps, that dims the light like a sandstorm dims our sun.

"However, we don't know what that material is [maybe it's remnants from a collision of planetesimals], or why it's causing a long-term dimming," Montet added. "We've seen disintegrating planetesimals before, but never something that looks like this. Kepler is the first opportunity that has given us enough time resolution and photometric precision to see these events; it looked at 200,000 stars [approximately] and found one of these, so it's pretty rare."

That pretty much takes the air out of the alien idea, but not the mystery itself.

If it's a cloud of some kind, it "would need to be at impossibly large distances from the star or be slowly increasing in surface density." That's not likely, the paper says. "Moreover, such a model does not naturally account for the long-term dimming in the light curve ... suggesting that this idea is, at best, incomplete."

Everyone involved says the truth is out there, but science is hard. Wrap your head around the fact that we can find planets orbiting a star 1,500 light years away. And then marvel at the complexity of solving a real mystery like this one. But we're trying. Over the next year, Tabby's star is going to get a lot more telescope time, and the attention of astronomy's big brains who say they are determined to find an answer to the mystery.

It's just a matter of time, according to Montet.

"The way the light is blocked during a large dip at different wavelengths will tell us a lot about what the material doing the blocking is," he told VOA "...is it a solid body, or a cloud of diffuse gas and dust? The LCOGT [Las Cumbres Observatory Global Telescope Network] is planning observations, and there are already a network of amateur astronomers through the AAVSO [American Association of Variable Star Observers] obtaining observations, which will be very important for understanding this system."

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