The mystery of Tabby’s star deepens

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Astronomers looking at the light variations of the star dubbed by some Tabby’s star have become even more baffled.

Spurred by a controversial claim that the star’s brightness gradually decreased by 14 percent from 1890 to 1989, Montet and Simon decided to investigate its behavior in a series of Kepler calibration images that had not previously been used for scientific measurements. “We thought that these data could confirm or refute the star’s long-term fading, and hopefully clarify what was causing the extraordinary dimming events observed in KIC 8462852,” explained Simon.

Simon and Montet found that, over the first three years of the Kepler mission, KIC 8462852 dimmed by almost 1 percent. Its brightness then dropped by an extraordinary 2 percent over just six months, remaining at about that level for the final six months of the mission. The pair then compared this with more than 500 similar stars observed by Kepler and found thata small fraction of them showed fading similar to that seen in KIC 8462852 over the first three years of Kepler images. However, none exhibited such a dramatic dimming in just six months, or a total change in brightness of 3 percent.

“The steady brightness change in KIC 8462852 is pretty astounding,” said Montet. “Our highly accurate measurements over four years demonstrate that the star really is getting fainter with time.  It is unprecedented for this type of star to slowly fade for years, and we don’t see anything else like it in the Kepler data.” 

At the moment, there is no good theory based on what astronomers know of stellar evolution to explain this star’s behavior. This does not mean the only explanation left is that aliens are building a Dyson sphere around the star, but it also leaves everyone at a loss to explain what is happening.


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  • PeterF

    What about the explanation that the hydrogen fuel is running out and the star is about to nova?

  • Localfluff

    Well, either create a new stellar physics. Or finally understand that the telescope has a broken pixel! It weakens over time. It sometimes dips deeply briefly. What ground observations are there to confirm this anomaly? 20% change in brightness must be relatively easy to observe even from the ground. Does everything depend on one single telescope watching 1 out of 160,000 stars?Really? (Where I live, Tabby actually means “mistake”).

    @PeterF Plain mid-aged F-stars don’t suddenly go nova, and nothing goes nova like this anyway. There’s simply something wrong with the telescope.

  • Localfluff: The data hasn’t been collected from a single telescope. It comes from multiple observatories. This is not an instrment error.

  • Localfluff

    @Robert Zimmerman
    Did it really come from multiple telescopes?
    I haven’t seen any sources for that. It would be interesting to do, if you have the opportunity to offer one. I think it is a (tiny) telescope malfunction.

  • Andrew_W

    As far as I know a small nebular moving between us and Tabby’s star still hasn’t been ruled out.

  • Brendan

    There was an earlier paper (don’t have time to look now) that looked at photographic plates from the last century and found it fading. There was some discussion that this was due to the plates themselves having problems, but I remember the author is considered an expert in historical analysis of plates, and stood by his work.

    If Kepler has confirmed this, then there are two sources for the downward dimming trend, and this has been going on for a century.

    I’m not saying its aliens, but….

  • wayne

    The paper is here– (I haven’t read it, but it is available.)

    ..big fan of Cats in Space… especially low & zero-g acrobatics.

    Slow Motion Flipping Cats –Smarter Every Day

  • Localfluff

    Yes, there it is. And its conclusion says:
    “There is no known or proposed stellar phenomenon
    that can fully explain all aspects of the observed light

    The slow dimming observed on historic photo plates and now in Kepler data, could have reasonable astrophysical explanations. Like maybe some dust passing between us and it. But the sudden 20% dips that got attention to begin with have shapes (ingress and egress) which cannot be anything but a malfunctioning telescope. No transit of anything can explain it. Those images were all taken in the same orientation, i.e. the same few pixels on the CCD were at the job all of that time. When the telescope was differently oriented, no dips occurred.

  • hondo

    wayne – thanks loads for the cat link. Checking out Smarter Every Day for more material for my granddaughter. great find.

  • wayne


    can’t take full-credit! But glad you enjoyed. Have a g-daughter myself, so I empathize.

    Yo– buy her the “Chronological Encyclopedia of Discovery’s in Space,” the author will sign it for you!

  • Brendan

    Wane –
    I laughed at the response (I suppose I could say I LOL’d but I am trying to resist the degradation of our communications).

    My daughter loves that picture, and it somehow shows up on all our phones and iPads…. Don’t know how she keeps getting my password…

  • Brendan


    “have shapes (ingress and egress) which cannot be anything but a malfunctioning telescope.”

    Or…. AWIENS!!!

  • Localfluff

    Not even “awians” look like that when they transit a star with something.
    The slow 100 year dimming could for example be a distant background star that from our point of view slowly moves in behind Tabby’s star. That’s something which might happen one out of the 160,000 stars Kepler1 stared at. Most explanations have the problem of something happening only one star. Not that historic photo plates have been as thoroughly examined for that many other stars (it is a tricky job since the chemicals have degraded over time and different chemicals were used as photography evolved and they have different sensitivity to different colors i.e. to different stars). It is a middle aged F star about 50% larger and heavier than the Sun and overall rather Sun like. It is not an exotic star, so any new heliophysics is not to be expected.

    The brief deep dimmings only occurred when the telescope was rotated in the same way (it turned 90 degrees four times per Solar orbit to keep heat shield and solar panels toward the Sun) and therefor a telescope problem is a likely explanation for it, and the only reasonable one proposed.

  • PeterF

    Aliens COULD be the explanation! They might be sending a smallest toward our star powered by a laser! Like in “The Mote in God’s Eye”
    Budget cuts and aging equipment over the years could explain the diminishing power…kind of whats happening to the DSN?

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