I hadn’t expected a new paper on KIC 8462852 quite this fast, but hard on the heels of yesterday’s article on the star comes “KIC 8462852 Faded at an Average Rate of 0.165±0.013 Magnitudes Per Century From 1890 To 1989,” from Bradley Schaefer (Louisiana State University). Schaefer takes a hard look at this F3 main sequence star in the original Kepler field not only via the Kepler data but by using a collection of roughly 500,000 sky photographs in the archives of Harvard College Observatory, covering the period from 1890 to 1989.
The Harvard collection is vast, but Schaefer could take advantage of a program called Digital Access to a Sky Century@Harvard (DASCH), which has currently digitized about 15 percent of the archives. Fortunately for us, this 15 percent covers all the plates containing the Cygnus/Lyra starfield, which is what the Kepler instrument focused on. Some 1581 of these plates cover the region of sky where KIC 8462852 is found. What Schaefer discovers is a secular dimming at an average rate of 0.165±0.013 magnitudes per century. For the period in question, ending in the late 1980s, KIC 8462852 has faded by 0.193±0.030 mag. From the paper:
The KIC 8462852 light curve from 1890 to 1989 shows a highly significant secular trend in fading over 100 years, with this being completely unprecedented for any F-type main sequence star. Such stars should be very stable in brightness, with evolution making for changes only on time scales of many millions of years. So the Harvard data alone prove that KIC 8462852 has unique and large-amplitude photometric variations.
That’s useful information, especially given the possible objection to the Kepler findings that they might be traceable to a problem with the Kepler spacecraft itself. Evidently not:
Previously, the only evidence that KIC 8462852 was unusual in any way was a few dips in magnitude as observed by one satellite, so inevitably we have to wonder whether the whole story is just some problem with Kepler. Boyajian et al. (2015) had already made a convincing case that the dips were not caused by any data or analysis artifacts, and their case is strong. Nevertheless, it is comforting to know from two independent sources that KIC 8462852 is displaying unique and inexplicable photometric variations.
As Schaefer notes, KIC 8462852 can now be seen to show two unique episodes involving dimming — the dips described here yesterday for the Kepler spacecraft, and the fading in the Harvard data. The assumption that both come from the same cause is reasonable, as it would be hard to see how the same star could experience two distinct mechanisms that make its starlight dim by amounts like these. The timescales of the dimming obviously vary, and the assumption would be that if the day-long dips are caused by circumstellar dust, then the much longer fading that Schaefer has detected would be caused by the same mechanism.
Image: KIC 8462852 as photographed from Aguadilla, Puerto Rico by Efraín Morales, of the Astronomical Society of the Caribbean (SAC).
Thus we come to the comet hypothesis as a way of explaining the KIC 8462852 light curves. Incorporating the fading Schaefer has discovered, a cometary solution would require some mind-boggling numbers, as derived in the paper. From the summary:
With 36 giant-comets required to make the one 20% Kepler dip, and all of these along one orbit, we would need 648,000 giant-comets to create the century-long fading. For these 200 km diameter giant-comets having a density of 1 gm cm?3, each will have a mass of 4 × 1021 gm, and the total will have a mass of 0.4 M?. This can be compared to the largest known comet in our own Solar System (Comet Hale-Bopp) with a diameter of 60 km. This can also be compared to the entire mass of the Kuiper Belt at around 0.1 M? (Gladman et al. 2001). I do not see how it is possible for something like 648,000 giant-comets to exist around one star, nor to have their orbits orchestrated so as to all pass in front of the star within the last century. So I take this century-long dimming as a strong argument against the comet-family hypothesis to explain the Kepler dips.
If Schaefer’s work holds up, the cometary hypothesis to explain KIC 8462852 is deeply compromised. We seem to be looking at the author calls “an ongoing process with continuous effects” around the star. Moreover, it is a process that requires 104 to 107 times as much dust as would be required for the deepest of the Kepler light dips. And you can see in the quotation above Schaefer’s estimate for the number of giant comets this would require, all of them having to pass in front of the star in the last century.
The paper is Schaefer, “KIC 8462852 Faded at an Average Rate of 0.165+-0.013 Magnitudes Per Century From 1890 To 1989,” submitted to Astrophysical Journal Letters (abstract).
Silly question but have the plates not deteriorated over time or perhaps a drift in magnitude ‘calculation’ occurred, it was a long time ago? I suppose this could be checked against a nearer star on the plate for errors or have I missed something.
15 January 2016
Comets can’t explain weird ‘alien megastructure’ star after all
Full article here:
https://www.newscientist.com/article/dn28786-comets-cant-explain-weird-alien-megastructure-star-after-all/
To quote:
Schaefer saw the same century-long dimming in his manual readings, and calculated that it would require 648,000 comets, each 200 kilometres wide, to have passed by the star – completely implausible, he says. “The comet-family idea was reasonably put forth as the best of the proposals, even while acknowledging that they all were a poor lot,” he says. “But now we have a refutation of the idea, and indeed, of all published ideas.”
“This presents some trouble for the comet hypothesis,” says Boyajian. “We need more data through continuous monitoring to figure out what is going on.”
What about those alien megastructures? Schafer is unconvinced. “The alien-megastructure idea runs wrong with my new observations,” he says, as he thinks even advanced aliens wouldn’t be able to build something capable of covering a fifth of a star in just a century. What’s more, such an object should radiate light absorbed from the star as heat, but the infrared signal from Tabby’s star appears normal, he says.
[So says a member of a species that cannot even get a few other members of its species to Mars in person, to say nothing of building a megastructure in space. We would not be talking humanoid-type beings wearing hardhats and spacesuits building something at this level of development. – LK]
“I don’t know how the dimming affects the megastructure hypothesis, except that it would seem to exclude a lot of natural explanations, including comets,” says Wright. “It could be that there were just more dimming events in the past, or that astronomers were less lucky in the past and caught more dimming events in the 1980s than in the 1900s. But that seems unlikely.”
My comment:
Kepler found something very unusual in its very narrow search range of the sky. This means we either got very lucky coming across what seems to be a rather rare celestial event or there are a lot of Tabby’s Stars and this is our first encounter because we only got a serious in our search for exoworlds just two decades ago.
And if it is artificial and there are a lot of them in the Milky Way…. I suddenly feel like the member of an ant colony at a construction site.
@Harry R Ray. Boyajian, et, al do not give a lot of information about their methodology concerning the DASCH data. My take at trying to read between the lines is that they were looking for short term variations, not a long term one. Schaefer’s method was to use only the blue sensitive plates and also cull any plate with quality flags. A 0.193 mag decrease over 100 years would be easy to miss as they would not be looking for it. The lack of any trend line the the comparison stars means the dimming Schaefer detected in KIC462852 is very likely real.
As Schaefer said, a long term magnitude change in a main-sequence F3 star is unprecedented, so Boyajain et al were probably not thinking along that line.
We’re incredibly lucky people. Our most imaginatively intelligent ancestors, from Eratosthenes to Sagan, would have loved to watch this remarkable mystery develop over the past five months. And this blog will easily continue to hook new readers attracted by smart, accessible posts and discussions.
It might be useful to those tuning in to summarize the highlights. Since abandoning haphazard headline news sources in favor of Centauri Dreams, I (think) I’ve learned that: KIC8462852’s Kepler-observed light dip patterns are too large and erratic to be consistent with normal orbiting planets. Allen and Spitzer telescope observations would detect significant energy noise or mid-infrared heat from an artificial structure or satellite swarm, and there haven’t been any. Lack of mid-IR heat also indicates that there is no post-planetary debris, dust field or “dark planet” close enough to the star to obscure its light as observed. The timing of WISE and Spitzer observations also rules out still-cool debris from a recent cataclysm blocking starlight. Multiple technical cross checks and long-term photographs of the star’s light strongly suggest that Kepler’s observations were not due to mechanical error. No telltale signs of a parasitic black hole. And an astronomically abrupt, yet observationally gradual, fade of the star’s light now makes the formerly leading cometary explanation unlikely.
Are there any other solid testable hypotheses to take the lead? Some have suggested non-radiative dust materials, or reconsidering the age and growth phase of the star. Or do scientists believe that a theory has been unduly discounted?
Small moves, Ellie. :)
@ H. Floyd Can we be certain that hypothetical alien structures would emit infrared in the wavelengths examined by Spitzer? Is it physically possible that they could be emitting in a different wavelength, and/or direction their emission directionally so that we can detect it?
Andrew Norman: I had the same questions until recently. In fact, I thought the ETI hypothesis assumed Dyson engineering will be so efficient as to be nearly invisible in the IR spectrum at that distance, the way I imagine fiber optics. But I think I picked that up more from sci fi than from actual sci.
Dr. Jason Wright, who produces perhaps the most reputable reasoning on Dyson structures, explained in a 2014 paper that thermodynamics just would not work that way, even with technologically advanced engineering. I understand that a physical structure blocking and harvesting that much starlight should have a full-surface MIR signature. That’s consistent with Dr. Mossimo Marengo’s comments elsewhere here, implying that direct observations of Boyajian’s Star by the Spitzer telescope’s Infrared Array Camera don’t support a Dyson theory. Here’s a link to that post and the discussion he kindly joined, including a discussion quote and reference to Dr. Wright’s paper that I found especially informative:
https://centauri-dreams.org/?p=34525
I have to add, however, that I may have easily misunderstood something. It’s theoretical astrothermodynamics after all, really not my day job. I’d be delighted to be corrected!
Alexander McLin January 15, 2016 at 12:38
” The second reason is, the Kepler light curves seem way too random, I envision mega-engineering would likely proceed in stages, stepping up from smaller building units to larger units. I would expect to see a more smooth distribution of dip depths corresponding to the unit sizes.”
One could always check if those random dip depths show some mathematical patterns ;) It’s a weird star, so why not if we are speculating? Won’t hurt, will it?
Or perhaps to put it more clearly, if we are open to all suggestions and speculations, what about a completely outlandish idea. What if instead of radio, or laser signal, here we have an optical one, using dimming of the star and dip depths as beacon to other possible inhabitants of galaxy? Of course this is a completely far fetched, but heck, if we are talking about Dyson Spheres, it could be a possibility too, why not?
Keep in mind I am just throwing this idea out, not posting it as something very plausible. But for fun why not check if the dip depths have a certain measurable pattern that is not completely random, one that would correspond to certain rules of physics, maths?
This ides was discussed in detail in Wright et. Al. Last year.
@ H. Floyd Thanks for the well reasoned response! My understanding is that if work were done with the energy collected, then waste heat would be produced. But what if the energy were transferred to a remote location, using some (nearly) perfect method of transfer? Would we then expect to see an IR signature at the site of the Dyson swarm?
@ H. Floyd Let me expound a little on my last comment…
Here’s a post from Wright, and he seems to make it clear that he’s looking for waste heat produced from work (powered by Dyson’s spheres) in his surveys:
http://sites.psu.edu/astrowright/2012/09/15/waste-heat-part-i-free-energy-limited-species/
When you’re looking at the scale of galaxies, as he has, then you would definitely expect the collected energy to power work in the same galaxy. (It boggles the mind to imagine power beamed from one galaxy to another.) However, when you’re talking about interstellar distances and civilizations of such technological prowess, then I can imagine scenarios where energy would be collected around one uninhabited, remote, star and beamed to another location where the free energy is needed…or perhaps many locations (or starships!) throughout the galaxy.
Thinking about Wojiech J’s comment and the provided quote.
I’m not sure we should expect clear patterning in the light curves. If this was the result of alien activity, the activity maybe rather more “organic” or decentralized rather than a centrally coordinated effort that would make some sort of simple and easily apparent pattern.
I haven’t looked at the paper, but is the dimming of the star linear? Or does it accelerate (like a pattern you’d expect of population growth, say if there’s some sort of nano-tech or machine replication that starts slowly then accelerates over time?)
FASCINATING!!!
Here is a way to think of SETI and astrothermodynamics. A Dyson swarm would be intended to harvest some substantial fraction of the luminosity of its host star. It almost cannot _store_ all that energy, so all of it must be released as heat from radiators at a lower temperature. This is the same physics followed by, say, dust that is heated by stellar radiation. However, unlike the case of dust or other natural radiators, the alien engineers have some control over the temperature of their radiators, and thus the thermodynamic efficiency of their swarm. This is true regardless of the temperature they are operating at (they can always set up a heat cascade to extract more usable energy, and have lower temperature radiators facing deep space), but if they are actually some sort of computational substrate, they may prefer to operate at cold temperatures (such as 30 K).
So, in my opinion the _temperature_ of the waste heat is a free parameter if you are assuming a Dyson swarm (it, of course, has to be > the black body temperature of ~ 2.725 K). What you _must_ have in a Dyson swarm hypothesis is a total energy flux (luminosity) in the IR that is a substantial fraction of the star’s total luminosity.
In the case of KIC 8462852, Figure 3 from Thompson et al. (see
https://pbs.twimg.com/media/CY0ijJ7UkAA2-dL.png and http://arxiv.org/abs/1512.03693) indicates that there could be an IR excess _equal in luminosity to the entire optical output from the star_, as long as the radiator temperatures are down around 30 K. As this is physically possible (alien thermal engineering may be very efficient, or the aliens might be computers running at < 30 K), I do not see how the existing IR data can be said to rule out a partial Dyson sphere about this star.
Sun spots fairly well ruled out so sorry to be a bit of a party pooper, the next most common cause of “false positives ” or as this isn’t considered to be an exoplanet, atypical results , is eclipsing binaries. And there is a precedent , KIC4110611. This presented not unlike 8468252 with an odd signal but turned out to be a system of not one or two but five close stars . Very atypical , but very natural. Still a reason to celebrate Kepler though, with its huge imaging vista turning up unusual, nee unheard of phenomena . With other big imaging planned in the future, astronomy will maintain its unique ability of turning up the unexpected. Exoplanets perhaps more than anything and one day that something atypical may indeed be what we all want . Even if it’s just two or three tell tale ( methane, ozone and molecular oxygen and a temperate planet ?) absorption lines on a atmospheric spectrum.
@Eric. I ran a weighted linear model fit OLS regression of Schaefer’s data using Mathematica.
I got a equation of 8.578+0.00198320x. The model fit was good with a R^2 (goodness of fit) at 0.97834. The ANOVA Table had F-Stat 574.014 and P-Value 2.2716X1-13 (both good).
I don’t know how to insert an image into this comment string, but I have two images of the data plot with the regression linein this Picasa album . The second graph is the fit residuals vs epoch (the title of the second graph is wrong).
IR excess seems inevitable for a “classical” dyson swarm and would probably have been detected. But what about a matrioshka brain? It should emit radiation very close to the temperature of the cosmic background radiation. Any thoughts on that?
https://en.wikipedia.org/wiki/Matrioshka_brain
@ Harry R Ray – You are entirely correct, and I thank you for that. I thought for some reason that Kepler 1 was in a region accessible by ALMA, but I was wrong.
In the Far IR, flux limits tend to be confusion limits, and an array would help remove the background and focus on the star. Maybe the CFA sub-mm array in Hawaii could help here https://www.cfa.harvard.edu/sma/ – being North of the equator, it should be able to see KIC 8462852 and it also can observe in the Far IR.
@ Marcel – Matryoshka brain are one reason why you cannot rule out a 30 K radiator temperature in the “Alien Engineering Hypothesis” (AEH).
It is important to remember that there is a “hole” in the IR data, and a large flux could be obtain by a large area of cold radiators and be consistent with the existing data. That is NOT proof (or even evidence) that this flux is indeed present – that needs more data. I wouldn’t get excited unless and until said IR flux is confirmed, not just possible. It could just as easily be refuted, and then the AEH becomes much less viable.
There is an AEH that is apparently viable – what data are needed to refute it? It would be exciting if the AEH were true, but first we have to test every conceivable alternative. The real point of all of this is to point out what future data need to be collected (or past data need to be analyzed) to do that.
What we are looking at was over 1,000 years ago. Who’s to say they aren’t wiped out by now hence the lack of IR?
The IR signal will have the same lag as visible light. Did you mean that they were wiped out before the visible light variations we’ve seen?
I haven’t read every previous comment, so maybe I am repiting here an idea previously posted, but:
– if we were an interplanetary civilization, with advanced technology so we have been wapping up our sun with the intention of building a dyson swarm and not let any radiation to get out of the star system,
-if we have been doing this for let us say the last 1000 years.
then, could not be possible that:
1) we have used materials or technology that emit almost no IR radiation, in an atempt to profit from every piece of energy from our sun?
2) since we have 1000 years of experience in this task, the present speed of the work is so high that in only one century we have made the star fade a lot, seen from a distant place in the universe?
3) if we asume that the speed of work will only increase with the time, maybe the work will be finished in a very short time from now, the fadding will be increasing more and more with the time, and maybe within the next 200 years the star will be completely hiden.
Mike, the IR is from over 1000 years ago too.
Both visible light and infra-red light are the same light travelling at c, only different range of the spectrum, they arrive at the same time.
You can’t win
You can’t break even
Why try?
So where is the heat…regardless of the cause of the dimming? The only thing left is the conclusion that this star is actually emitting less light…i think
Could losing mass to a black hole in a common envelope or contact binary type situation explain the gradual dimming. seen from top or bottom that is.
fun stuff.
To Marshall Eubanks you are correct about visible light and infrared traveling at the same speed. However I think your comment was intended for Marc Longoria.
@Frank Smith – THANKS. Looks pretty linear, at least at the (short) timescales in our sample.
Very unlikely that the weirdest star in the galaxy just happens to be in Kepler’s tiny sampling of the galaxy. Whatever this is, in all likelihood, there are others.
I think we’re in for a very long haul mystery here, and I won’t be surprised if this remains unresolved for more than 50 years. We may have to wait for a stellar focus mission to get a really good view. One of the fascinating issues, especially with the above speculation about the IR signature of a Matryoshka Brain, centers on the fact that we have very few solid criteria to discern artificial or living activity from the workings of dead/inert matter and energy one of the fascinating things about looking for evidence for aliens. Unless aliens wanted to make themselves very obvious to us (signaling ala SETI), then we’ve got to contend with the ambiguity of our evidence.
Karl Schroeder’s thoughts are important. To him “any sufficiently advanced technology is indistinguishable from Nature” (see: http://www.kschroeder.com/weblog/topics/The%20Rewilding). If so, we’re going to have a very, very hard time resolving what’s going on at this star.
Marshall, thanks for clearing that up.
Could the dimming be explained by something on the line of site between us and the star, but not near the star? Say, a brown dwarf with a dust disk around it? The dust could be quite cool (as it would not be heated significantly by the F3 star). It would require a coincidental alignment of the two systems, but then Kepler was looking at a lot of stars, so maybe that’s ok.
From what I understand, main sequence stars tend to become brighter over time. Are there any natural models to explain this dimming? Star behavior hasn’t been completely figured out, so maybe this is a new process.
It could also be an advanced alien civilization harvesting energy 1,000 years ago, but I’d rather consider every mundane, natural possibility before I assume ETI.
No. The models for main sequence stars, which are really good models BTW, do not predict this sort of behavior at all. Could it be an outlier? The modelers may want to go back and look at the possibility.
@ xcalibur
As you can see, pretty much everybody are seriously trying hard to find “mundane”, a.k.a. scientifically sound explanations for this phenomenon before anything else.
You can probably forgive us for having an imagination and curiosity, in addition to rigour.
Andrew Norman: You make a really key point. It looks like Dr. Wright isn’t actually saying that Dyson engineering will radiate IR simply in obedience to some immutable physical law. Instead, that part of his reasoning sounds economic, or even biological: We should not expect Dyson engineering to be cool in the IR spectrum because cool engineering wouldn’t be cost effective under those circumstances. But that doesn’t prevent the engineering from channeling or even concealing IR heat for some other reason.
As a guiding principle, there’s something compelling about Wright’s rationale notwithstanding. In our biosphere, evolution has never favored efficiency for its own sake. It strongly favors designs that are just efficient enough to convey some key advantage within a niche. In humans’ case, it appears that we beat out a cluster of similar hominid species by just a handful of daily average calories per reproductive generation, until we gradually proliferated and dominated. Our technology (albeit the only example we have) seems to follow a similar pattern of development. In the long run, just good -enough- proliferates, and fine engineering is almost by definition an outlier, a luxury. By that principle, it makes sense to expect Dyson technology — absent some other existential pressure — to shed excess work energy at whatever point it’s no longer cost effective to recover it. Dr. Wright predicts that in Dyson engineering that point would be in the MIR. (I’m comfortable accepting that last bit on his good authority; I don’t know enough about thermodynamics to critically evaluate it. But I’d like to hear alternate views if they’re out there. It could turn out to be one of the most significant premises in the study of KIC8462852.)
It’s very risky to draw parallels between biology and technology. But Dr. Wright’s confidence in predicting that Dyson “work” won’t be efficient to the point of invisibility in the IR spectrum, essentially because that would not be cost effective, feels like a sound guiding principle.
That said, principles aren’t laws. Principles are supposed to help us solve mysteries. And this mystery has reached a point where it now seems fair to add additional assumptions to the hypotheses. Cleaner theories haven’t explained this one. You suggest an additional assumption that’s hard to overlook.
Here’s the crux of that quote, via hindsight and the miracle of nested commentary:
“Thus, while an alien civilization using starlight might emit waste heat over a range of temperatures, we should not expect it to be so cold or to have such a strongly non-thermal spectrum that as to be easily missed in the MIR.” Wright, et al., 2014b, Part 2.6.4.
I’ve been corrected in my reading of that. In light of Dr. Wright’s subsequent explanations here, “easily” is a key qualifier. Negative MIR observations are (maybe) informative, but still not enough to rule out Dyson engineering at KIC8462852.
@Marcel, Frank etc
Perhaps the 100 year fade on the star is not caused by it being obscured, but its actual brightness changing. There would be a common cause – I saw mention somewhere that there is another star nearby. What if it had recently transited through the system and passed extremely close to the KIC star. Could tidal forces then make the star shine much brighter for a while by disrupting its atmosphere etc? If that is the case then it could either be returning to its proper brightness, or the 100 year dip could be part of a ~500 year decaying sinusoidal oscillation that will now go on for thousands of years.
The stars transit would cause both the comet disruption and the star disruption.
A number of people here have suggested changes to the level of the star’s radiated light itself, bypassing the need for light to be blocked by external causes such as comets. Unfortunately, the type of changes we see with this star have NEVER been seen in main-sequence stars.
A main-sequence star’s light is generated in its core from nuclear fusion, and takes million of years to reach its photosphere and radiate away. Any short-term (meaning less than tens of thousands of years) fluctuations in the amount of energy being produced get averaged away during the “random walk” of the photons making the journey from the core. So the total bolometric luminosity (which counts light at all frequencies) over time scales between a year and 1,000 years should remain steady.
Intrinsic pulsating stars do emit radiation at different levels over the course of their pulsation cycle, but these cycles are invariably less than a decade or so, and the luminosity at a given point in their cycles remains constant, so the time-averaged luminosity (for times that are a multiple of their cycle time) does not change.
Other variable shift their radiation between different frequencies. For example, some stars experience random dips in their visual brightness, much like this star, but in their case the cause is clouds of carbon soot forming in the upper photosphere and blocking the visible light. However, the light simply shifts to infrared, and the sum of visible and infrared light remains the same. This is not the case with this star.
Other variables exhibit random INCREASES in their luminosity, usually due to thermonuclear explosions in the stars outermost layers. These are called cataclysmic variables, and are fairly well understood — the explosions are often due to extra hydrogen being dumped onto their surfaces from closely associated giant stars. But this star is obviously not one of them.
Bottom line, there is NO known internal mechanism that produces either the random dips in brightness and no changes in IR radiation, or the secular decrease in brightnes over a timescale of centuries. So it must be external, in the form of something outside the star blocking the light (without re-radiating the light as detectable IR, so it must be too cold for the IR to be detected so far).
Comets are virtually ruled out, so what does that leave? Either some unknown natural phenomenon (this is my personal expectation) or a large-scale artificial construction effort, at some distance from the star so that the re-radiated IR is sufficiently low frequency that we have not detected it (or possibly emitted directionally so that it’s not aimed in the direction of Earth at all).
@ Paul Carr
I know that Dr. Schaefer said that the Harvard group had looked at some great number of scanned stars, and didn’t see any similar magnitude shifts. However, they didn’t apply his filtering and averaging (what he calls binning) technique.
I confidently predict that within the very near future the DASCH group (or an affiliate) will be applying the Schaefer technique to every star in their database. Let’s hope they come up with at least a few more candidates with similar magnitude shifts. (Kepler may have been lucky enough to look in the right direction to see the only such star in the galaxy, purely by chance, but that’s not the way to bet.)
Oh, and here is an early report on the Harvard / CFA effort in the New York Times
http://www.nytimes.com/2007/07/10/science/10astro.html?_r=0
Paul Gilster: This may NOT reflect the REALITY ofthe situation, but, just for fun, someone should do a “Fade To Black” thought experiment using the available data. To put it simply, assume that the apparently linear progression continues ad infinitum without deviation, how many centuries or millenia would it take for KIC8462852 to become UNDETECTIBLE in the visable light spectrum! Then, TURN IT AROUND and assume that the cause of the dimming started in the distant past and progressed to the FIRST DASCH plate in 1890 in a similar linear progression. Could we determine what PERCENTAGE of starlight is CONTINUOUSY BLOCKED regardless of ANY(major or minor)fluctuations in the Kepler iight curves. The reason I bring this all up is, I HAVE A BOLD PREDICTION: In midsummer, when the FIRST GAIA data will be available in a usable form, KIC8462852 will be found to be LESS THAN A THOUSAND LIGHT YEARS AWAY, and NOT 1,480 ly, as calculated by less sensitive methods at present. If I am right, to fit the luminosity to the stellar type(F3V), at my hypothesized distance, it could be that as much as FIFTY PERCENT of the light is blocked ALL THE TIME by …………..something!
I have a new idea I haven’t seen proposed anywhere else.
What would a star system look like if an F star like Tabby’s were hit
by a massive object like another star, or a supergiant planet?
We would see ejecta from the star, and as the ejecta escaped gravity
it would become colder, progressively dimming the star (on average)
but material would be unevenly scattered around the star’s orbit.
Initially this ejecta would emit essentially the same radiation the
star normally emit, made of exactly the same matter, and initially
having the same temperature and radiation in general.
The violent the collision, the larger the mess. I’m thinking maybe a
brown dwarf slingshotted directly into Tabby’s.
Have you heard anyone proposing anything like this?
Paul: Jason Wright just tweeted that KIC8462852 is now 20% fainter than in 1890! That means that the FIRST PART of my proposed “thought experiment” is immediately solvable. In just five centuries, Tabby’s Star will FADE TO BLACK! It would STILL be fun(and perhaps INFORMATIVE as well) for someone to do the SECOND PART OF IT!
There is a good discussion with Bradley Schaefer in this new episode of The Wow! Signal Podcast:
http://www.wowsignalpodcast.com/2016/01/season-3-episode-3-slow-and-fast.html
He reiterates that many main sequence F-type stars, up to millions, have been examined and this phenomenon has never been seen before. Weird.
Harry, a fascinating thought experiment indeed!
All very weird.
My improbable theory (in my defense, all theories are improbable).
A planetary nebula around a rogue planet between us and the star, maybe even orbiting the star in a 100’s of AU deep orbit. Far enough from the star as to not show in IR, slow enough crossing the line of sight to take hundreds of years, extensive enough and lumpy enough to show the observed light curve.
Big problem is could such a thing exist in such an old system?
Feel like I’m scratching about trying not to resort to ET.
How is KIC8462852 20% fainter? There was a loss of 0.165 magnitude per century. It would take roughly 600 years for the star to be one magnitude fainter…
Horatio Trobinson: Jason Wright is currently mulling this idea, but with the Red Dwarf “companion immaged by Keck INSTEAD of your Brown Dwarf. Follow his tweets as Jason Wright@AstroWright. Heck, EVERYONE follow his tweets until this is resolved!!!
Frank Smith: Star magnitudes are calculated on a logarithmical scale, so a drop of about .2 magnitude does equal about 20% loss of brightness. A one magnitude drop means about 60% fainter, a two magnitude drop equals about 85% fainter, a five magnitude drop means 99% fainter, a ten magnitude drop means 99.99% fainter and so on.
“Big problem is could such a thing exist in such an old system?”
To answer my own question, since Saturn’s rings are thought to be as old as the solar system, why not?
So I’m thinking a dark companion to KIC8462852 hundreds of AU from the star with its own planetary system, including ringed planets, such planets could perhaps be moving quickly enough about their primary to pass between KIC8462852 and us in a day, with the denser dust in the system causing the century long dimming.
I assume that without a hot star to blow dust away a dusty planetary nebula could be stable for billions of years.
@H. Floyd. Thanks for the thoughtful discussion points! Biological organisms are not designed so it’s true that often operate inefficiently, just well enough to be competitive. But inefficiencies in engineered devices are the result of limited knowledge/experience/available technologies (at least that’s my understanding, I’m a biologist, not an engineer.) I don’t think it’s true that more efficiency is necessarily less cost effective.
I would expect that very advanced civilizations would have solves the technological hurdles for near perfect efficiency, and would have no reason to build anything less effient.
I had a request on Twitter to discuss whether the lack of observed IR excess emission rules out alien engineering. The bottom line is “not really”. Part of that is because we don’t know what alien engineering can do, so it that hypothesis can sort of survive any datum. Most of it, though, is just that the waste heat we expect to see (from *any* absorber, artificial or natural) could be cold, or beamed, or radiated away from us.
The bottom line is that all of the blocked energy has to go somewhere. Here’s where it could go:
1) The most natural explanation is that it is converted to high entropy waste heat. This is what ultimately happens to virtually all sunlight that strikes the Earth, and virtually all energy generated by humanity (we retain a tiny fraction chemically in plastics or buried biomass, or in gravitational potential in buildings, or radiated into space as radio waves, for instance). It’s also the case for energy absorbed by dust or comets or whatever. In this case, there are two ways to “hide” it from WISE, Spitzer, and other instruments:
a) Reradiate it away from Earth. For instance, if alien radiators are pointed at their ecliptic poles, and Earth is in their ecliptic, then we would see very little of it. Some of our spacecraft do this, so it’s not an arbitrary explanation, but you wouldn’t really expect it from natural sources.
b) Emit it at very low temperature. For megastructures, this requires very large panels, probably very far out from the star. For natural explanations, it means that the absorbers exist far out like a ring of cold material (still my favorite explanation). The implied orbital velocity of the dips that Tabby’s Star showed in Kepler is very slow, so the equilibrium temperatures might be estimated to be pretty low (~100 K or so, very roughly). Low temperature implies long wavelength, and if the temperatures are much below 100 K then even WISE won’t see it. This is where something like ALMA might help. To bad Herschel is not operating any more.
2) The energy is radiated away at low entropy, or stored in some way. This means it could be beamed and/or coherent, like a laser or radio signal for communication or propulsion. Unless the beam is pointed at us, we won’t notice this low entropy radiation. In this case, there is a maximum efficiency for this process (since entropy of the energy cannot go down (2nd law and all) dumping some of the energy at low entropy means you must dump the rest at high entropy, so we’re back to waste heat). In this case, you dump much less energy as IR radiation, but not arbitrarily less. For temperatures of ~100K or so typical maximum efficiencies for starlight are around 90-99% (colder=more efficient), meaning you’ll get 10-100x less IR emission than in case 1). Again, the excess could be cold or out-of-plane, as in cases 1a) or 1b), further reducing the signal.
3) Finally, the ETI exotica we can’t rule out, but can’t really test for either :
a) Non-EM radiation: it could be converted to neutrinos or something.
b) Energy-to-mass conversion: this is essentially super-efficient energy storage. Kind of a waste though, since if you wanted mass there’s plenty of it right there in the star, or in whatever you’re making the absorbers out of— there’s no reason I can think of to make piddling amounts of mass out of starlight. At any rate, in this case you’re still limited by the efficiencies in case 2).
Also, let’s be clear what “efficiency” means here.
Computers today are *much* more efficient than they were in the past. But this does not mean they give off less heat; we use that efficiency to squeeze more cycles out of every erg, but when we’re done with those ergs we still dump 100% of that energy into waste heat. Biological organisms are very efficient in many ways but, again, almost 100% of the calories we consume eventually come out as waste heat. Your car might get great gas mileage, but unless you’re running a hybrid, 100% of the kinetic energy of the car gets dumped into the air and the brake pads every time you stop (and, ultimately, radiated away as waste heat by the Earth).
So don’t confuse “efficiency” in the everyday sense of the term with global thermodynamical “efficiency”: unless the energy is stored (not a long-term possibility) or beamed away in a low-entropy manner, it’s all going to come out as IR radiation, no matter how “efficient” the machine doing the work is.
While orbiting alien superstructures is much more exciting to think about, perhaps intrinsic variability deserves a further look. How many low-metallicity F3 stars have been checked to see if they have slow-motion luminosity variations? If it is a periodic variation, lasting say decades, is the data good enough to verify the non-existence of such variations for all such stars except this one? If it represents some transition in chemistry of the corona or another layer, is there any possibility that the transition might have some instabilities in it, accounting for the dip or more generally, leading to a change in some other layer which would be unstable? Instead of looking for a common cause for them, maybe the dimming should be thought of as the driver of the dip. There are 10-20 different mechanisms known which create periodic variation of luminosity, but since there is a selection effect to find the short term ones first, there may be one more remaining to be found.