Metzger, Shen, and Stone

The next round of WTF star papers continues.  Brian Metzger (whom I know from grad school), Ken Shen, and Nicholas Stone have submitted a paper to MNRAS exploring in detail the idea that that Boyajian’s Star is dimming secularly because it recently “ate” a companion, and it’s still processing the energy from the merger, which is slowly “dribbling” out as an excess of luminosity.   

Steinn and I explored this in our rundown of possible explanations.  It appeared as hypothesis 13 in my blog post as “post-merger return to normal” and in our paper in section 11.3.

We had two primary objetctions: it would not really explain the dips, and the timescales are all wrong.  We wrote:

One issue here is that the dimming is too fast.  When confronted with big changes in energy content or flux, stars evolve on the Kelvin-Helmholz timescale, roughly the time it takes for all of the energy in the star at a given moment to finally escape the surface (while being constantly replenished by the fusion in the star’s core). For Boyajian’s Star this timescale is about 1 million years. This means that if the entire star is processing a big change in internal energy or luminosity, it takes around 1 million years to complete the adjustment.  Changing by 15% in 100 years is therefore about 10,000 times too fast.

But, the star’s radiative envelope is not very massive, so perhaps the energy never made it deep into the star? In that case the Kelvin-Helmholz timescale is a bit shorter, so maybe we’re off by only 1,000 times. It’s an order of magnitude argument, so maybe we’re being too pessimistic by a factor of 10, so we’re only off by 100 times. It’s possible that a detailed simulation of such a merger will reveal shorter timescale events, perhaps even things that might produce the dips.

So, I’m intrigued, and I like the idea despite the timescale argument not working out. It’s possible that there are other ways to temporarily brighten a star we haven’t thought of.  I’d like to hear from people who model these things before I commit to a plausibility level, so I’ll say:

Subjective verdict: unclear.

Well, Brian Metzger and company have come through.  In their paper, they look at the same mechanism Neslušan and Budaj explored to put material on highly eccentric, “cometary” orbits around the Boyajian’s Star.  The idea is that the close companion (which is presumably bound to Boyajian’s Star) interacts with material (anything from comets, planets, brown dwarfs to other stars) and slowly perturbs it into a highly eccentric orbit.  Then, if it’s comets, it outgasses when it gets close and you get the big dusty comae that might cause the dips.

Metgter et al. invoke the same mechanism to put a heavier object on an eccentric orbit, then have that object merge with Boyajian’s Star.  They deposit the energy into the envelope of the star, then run a stellar structure and evolution code called MESA to see how the energy is processed.

Their key result is their Figure 2:

screen-shot-2017-01-03-at-8-51-53-amIt shows, on the top, the total brightness of Boyajian’s star after merging with four fiducial objects of very different sizes.  The extra energy here is coming from the object’s orbital kinetic energy, which gets dissipated as heat when the two objects merge and eventually comes out as starlight.  Bigger objects have more energy to deposit, and deposit it at different levels.

The bottom plot shows the fractional change in the star’s luminosity with time (it’s the time derivative of the top plot divided by the top plot).  Zero means the star is not changing brightness, -0.01 means that the star changes its brightness by one e-folding (a factor of 2.7) in about 1/0.01 = 100 years.  The grey bands are the long-term dimmings seen by the DASCH plates over the last 100 years (top) and by Kepler over 4 years(bottom).

Steinn and I argued that the values you get in this scenario are more like -10-6, so way too small to notice.  What Metzger et al. have shown is that most of the energy does indeed end up in the envelope—the top millionth of the star’s mass—so time timescales are correspondingly shorter.  Our order of magnitude estimate was way way off, and so the hypothesis may be plausible after all (we recognized this could be the case in our paper, which is why we declined to give this scenario a plausibility).

So there are regions of the graph where all four curves cross the secular dimming levels seen.  This means that the model does not have to commit to what merged with Boyajian’s Star to explain the dimming.

So where does this scenario rank now? There are still several details to be worked out:

First, there’s the dips.  Metzger et al. point out that the same mechanism that sent the object into the star could also send other material there — a big planet could have lost its moons during a merger, or a planet could have been ripped apart, or something similar. This is essentially Boyajian et al.’s original hypothesis of material on a cometary orbit due to a single disruption event. The big difference is that there was originally a lot more material in the form of something that fell into the star.

Then, there’s the lack of infrared flux.  Again, the highly eccentric orbits save the hypothesis, and Metzger et al. point out that stellar radiation will blow sufficiently small dust out of the system, where it would no longer be warm and radiate.

The next is the details of the Montet & Simon light curve.  It changes slope pretty dramatically, and overall is steeper than the Schaefer dimming. What does this imply? I don’t see similar changes in slope in the Metzger et al. models, but presumably they’re invoking multiple ingestion events. Is this a problem for the model, or does it perhaps tell us the timings and masses of the mergings?

The next is the luminosity. The European Gaia spacecraft will measure the distance to the WTF star very precisely. This, combined with its apparent brightness, will give us the total luminosity of the star quite precisely.  This should give constraints on the merger history of the star.  Combined with the various secular dimmings, this should constrain the model—or prove inexplicable.  It would be nice to know what Gaia weill tell us, if anything, about this model. It would be especially nice if this model turned out to make a falsifiable prediction for the parallax.

Finally—and Metzger et al. acknowledge this is a major flaw in the model—there’s the issue of how likely this is to happen.  Steinn and I have argued that whatever the explanation for Boyajian’s Star, it’s got to be an unlikely one because it’s unique among 200,000+ stars Kepler has observed.  But this scenario turns out to be really unlikely—like Kepler had all but zero chance of seeing such a thing happen.  The effects of these merging events don’t last very long, so you need to stare a long time to have any chance of catching it happen. You would need practically every F star to have planetary material ready to go on eccentric orbits and merge, and even then you need a lot of planetary material.

I’m glad to see this scenario fleshed out so well. I suspect that there are ways to save the model by finding ways to make sort of event occur more frequently—perhaps by making the merging/dips more frequent by getting a chain of material from a single massive object—so I’m optimistic there’s more to this.  I’d say this paper has moved the “post-merger return to normal” scenario from “unclear” plausibility to something like “less plausable,” or even higher.

As I wrote last time:

This is how Tabby’s Star will be solved: a vague and qualitative hypothesis will get turned into a simple, quantitative model like this one, and that model’s success will inspire further work on more complex quantitative models. Eventually, these models will explain all of the data well and make some sort of prediction that will be confirmed by observations. Then we’ll say we have a good model for the system.

12 thoughts on “Metzger, Shen, and Stone

  1. dryson

    Because honey bees see only six frequencies of light plus Bee’s Purple would the Honey Bee possible be able to determine if a planet is habitable or not?

    How the project would work would be to take a photo of the frequencies give off by Earth that has life on it and images of the Moon and Mars and place them side by side.

    If the theory is correct more honey bees would converge on the image of the Earth than the other two images because the frequencies of light emitted by the image of Earth would fit into their six color range.

    Also if a planet is discovered and has Bee’s Purple that only a honey bee is able to see then the planet might be capable of supporting life because there could be flowers on it that produce the same light spectrum as the Bee’s Purple.

  2. Dryson

    Glass can bend over and over again on a nanoscale

    Brigham Young University researchers have developed new glass technology that could add a new level of flexibility to the microscopic world of medical devices.

    Led by electrical engineering professor Aaron Hawkins, the researchers have found a way to make the normally brittle material of glass bend and flex. The research opens up the ability to create a new family of lab-on-a-chip devices based on flexing glass.

    How would Mormon Flexible Glass placed around KIC 8462 in a Dyson Sphere configuration effect the light curve of KIC 8462 as well as the flux?

  3. Dryson

    A mega structure doesn’t necessarily mean a structure built of steel and wires. A mega structure can mean a large structure of words.

    I recently watched the movie Arrival very interesting movie if you know what you are looking for. This is an interesting theory to the light curves of several stars that have mysterious dims that cannot be explained.

    Why were Sheena Easton sites used?….See…She….He…across the distance of the sea.

    How an alien civilization might communicate with Earth.

    The very first sense that a newborn uses upon emerging from the womb is its eyes as it encounters light for the very first time. An alien civilization having discovered Earth but not wanting to disturb our natural evolution would understand that the simple sense of sight would be a common language foundation or speech through seeing.
    Hearing would be the second sense with touch and smell and taste to follow. But the two primary foundations of a language would be sight and hearing that like the letter A would form the legs of the letter A to a single point of understanding. The bar in the center of the letter A is to ensure that the rigidity of the foundation is remains connected at the simplest forms of communications and to not get to communicated with dual meanings of words.
    In 1977 the Voyager program launched into space to explore what we call Deep Space, or the space beyond Pluto. On both of those spacecraft were Golden Records that described humanity and Earth and where Earth was located thus achieving the first foundation of communication between an alien civilization through sight.
    An advanced alien civilization would know how sound is created based on a guide wavelength’s, depth. width and length that would allow the aliens to understand what was on the record.
    Like I mentioned sight is the first sense that an infant uses when it comes from the void into the light. Humans looking from the Earth into space is much like the infant seeing for its first time. An alien race would design its language based on sight first as a mutual understanding as a formal base of communication.
    Because light travels very far and very fast through space and has a less likely chance to degrade across time and since sight is the first sense that we use an advanced civilization would use the largest source of light that we can see in space to communicate with.
    A sun.
    A sun emits light based on its own rhythm but there are several stars that are experiencing mysterious light curves or dims that cannot be explained as there is not any celestial objects interfering with the suns to cause the dims. The only explanation can be that something is manipulating the sun’s light curve to create a language that humans can first see.
    Stars that have mysterious dims that cannot be explained are:


    The closest sun is RIK-210 at approx 470 light years from Earth.

    In all three mysteries the numbers, 0,1,2,4,6 and 8 are present in the first three and four numerical values.

    All of these stars have dims that have increase mysteriously that much like the wavelength of sound can converted into sight at the speed of light.

    Going back to the Golden Record and how a record is made. Each sound that is recorded on a record has left and right wave channel that the stylus travels across to create the desired the sound. If the light curves of the three suns listed above are treated like the wave channels where the length, depth and distance are converted into wave channels and a stylus then travels through both left and right wave channels then a message might be present that an advanced alien civilization is using to try and communicate with humanity.
    The link below shows a record and stylus at 1,000 times magnification. If you look close enough at the outside edges of the wave channels a 2D wavelength is formed that is very much similar to how a light curve of a sun would look in 2D.

    If the light curves of the above three mysterious suns are placed together in various combinations such as the right channel of RIK-210 and the left channel of EPIC-2042 for example then the Golden Record of the aliens trying to communicate with humans might be present.

  4. Dryson


    A young star has been seen having episodes of dimming. The star is RIK-210 and it is around 472 light-years away from the Earth. A star will sometimes dim whenever an object would pass by it. That is how some planets have been found, by the dimming to causes to the star as it passes in front of it.

    However, there is no planet near RIK-210 to explain for its dimming. It also doesn’t have any nearby star that might cause it to be dim. RIK-210 is said to be around five to ten million years old and half as massive as the Sun.

    RIK-210 is only 472 LY away from Earth and would be a better study to determine what is causing the light curve of KIC 8462

  5. Dryson

    Atmospheric Refraction

    Atmospheric refraction is the deviation of light or other electromagnetic wave from a straight line as it passes through the atmosphere due to the variation in air density as a function of height.[1] This refraction is due to the velocity of light through air decreasing (the index of refraction increases) with increased density.

    Could it be possible that a gas, other than air which is obviously not in KIC 8462’s atmosphere, be responsible for causing the light from KIC 8462 to deviate thus causing KIC 8462’s light curve to decrease?

    What interactions, naturally occurring first and artificial second, within a Sun like KIC 8462 could create an atmosphere that would refract the light from KIC 8462 passing through it?

  6. Dryson

    An interstellar black hole disk? Maybe!
    Although a black hole is definitely not eating up the light from Boyajian’s Star, there’s another way a black hole could be blocking the light. Maybe there’s something big and dark in the interstellar medium between Boyajian’s Star and Earth.

    A disk of material orbiting a black hole is one possible explanation. (Debris disks also orbit stars and planets, but since astronomers don’t see anything like that, this object would have to be dark … such as a black hole.)

    For this hypothesis to work, the disk of material clotting around the black hole would have to be huge–something on the order of 600 times the distance between the Earth and the Sun–in order to block the star’s light for such long periods of time, despite the star’s monthly movements.

    Material within the Black Hole Disk must act like glass in order to cause a continual decrease in light over 99 years of .1414% each year for 99 years. This means that the material density of the disk must have became larger over 99 years causing the decrease to reach a peak of 14% and then 20%

    This section would explain the theory better.

    Refractive Index
    You’re probably familiar with the concept of “traveling at the speed of light”, but did you know that the speed of light can change? Light’s speed is reduced when it travels through a medium due to the interaction of photons with electrons. Typically, higher electron densities in a material result in lower velocities. This is why light travels fast in glass, faster in water, and fastest in a vacuum. The refractive index (n) of a material is defined as the ratio of the speed of light in a vacuum to that of light in the material.

    But when Kepler took it readings the light decreased by 3% (14% to 17%) over the four years of the Kepler mission. That is a .75% increase in the decrease on yearly basis compared to the 99 years increase of the decrease of the light curve of .1414%. The difference is .6086% which over 99 years would equal a .006147474% decrease in the light curve of KIC 8462. An object would be too small to register such a decrease in the light of the sun at .006147474%

    The sudden increase in the decrease of light from KIC 8462 over four years compared to 99 years would either be the result of an extremely dense section of the disk having material similar to glass that would effect the light of KIC 8462 or a large section of plate glass meant to collect light and convert it to electrical energy.

  7. Dryson

    I was looking at the location of KIC 8462 again and noticed that KIC 8462 is located within the boundary of three different stars that form a right triangle.

    1. Deneb – , A2 star.
    2. Rukh – , B9 III + F1 V star, A B-type main-sequence star (B V) is a main-sequence (hydrogen-burning). An F-type main-sequence star (F V) is a main-sequence, hydrogen-fusing star
    3. Sadr – , F8 star.

    1. Could the position of KIC 8462 within the Triangle of Tabby’s Star create reactions with KIC 8462 that would cause the star to dim?
    2.Could Rukh being a Combination star affect the brightness of KIC 8462 seeing as how KIC 8462 is rather close?
    3. I looked up the difference between hydrogen-burning and hydrogen-fusing stars and really couldn’t tell the difference.

    If there are slight difference between hydrogen-burning and hydrogen-fusing stars could the process of Rukh somehow be siphoning off of the energy of KIC 8462 causing it dim?

  8. LocalFluff

    I’m sorry, but Tabby’s star will be solved by being slowly forgotten. It was a peryton, a malfunction somewhere in the process of making the observation, and it will never be confirmed by a new observation. I’m just advising you to be mentally prepared for that and to not sacrifice too much more of your career on this hype. (It might be ridiculed one day) Please keep up the good work instead!

  9. Dryson

    The accretion disk of a compact object in Cygnus X-1 might be what is causing the dims of KIC 8462.
    If KIC 8462 is acting as if it is an oblate star based on its light curve then perhaps the accretion of disk of the Compact Object is transiting in front of KIC 8462 causing the light of KIC 8462 to appear to oblate but is in fact being obscured by the Compact Objects accretion disk.

    Are there any other objects close to KIC 8462 that might effect the light curve of the star even though the star and the object my be 4,000 light years apart?

    I’m still holding out for aliens though.

  10. EricSECT

    Thanks Jason, I’ve a question.

    You wrote “… it’s got to be an unlikely one because it’s unique among 200,000+ stars Kepler has observed.”

    So can we categorically say that the entire Kepler database has been thoroughly, and MANUALLY examined to glean out any other light curves as weird as Tabby’s, and that we observe NO other stars exhibiting such weird behavior?

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