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I was wondering about the light dimming of the 'alien megastructure' star. From what I understand, for it to be a planetary body, it would have to be some 20 times the size of Jupiter. Is it possible that it could be caused by some huge, dense gas cloud, orbiting around the star?

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    $\begingroup$ The smallest star, a brown dwarf, would only have about 15% larger diameter than Jupiter. Throw more mass into Jupiter and it will only get denser, not much larger. Whatever it is, it is not a planet. $\endgroup$ – LocalFluff Jan 28 '16 at 20:47
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    $\begingroup$ That's no moon... $\endgroup$ – 3therk1ll Jan 28 '16 at 20:47
  • $\begingroup$ Sorry. Couldn't resist $\endgroup$ – 3therk1ll Jan 28 '16 at 20:48
  • $\begingroup$ I didn't get the joke anyway. You know, I'm apparently a nerd. $\endgroup$ – LocalFluff Jan 28 '16 at 20:49
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    $\begingroup$ Heh, I'm not nerd enough to make that association in my head spontaneously! The only thing we'll see of a 1000+ year old Death Star under construction is a heat beam which immediately cooks us. Maybe we have a chance of getting some life out of its destructive way. $\endgroup$ – LocalFluff Jan 29 '16 at 14:18
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No.

  • The light curves don't look at all like anything transiting. The ingress and egress profiles and the timing are way beyond that kind of explanation. Not planets, not comets, not clouds, not alien super structures.

  • No infrared light from dust or gas has been detected, as they should've been if the starlight had heated small particles. And since this is an F star with about 50% larger diameter than the Sun, which contains 99% of the mass in our Solar System, you can imagine how huge any comet/dust/gas cloud has to be to cover 22% of it.

  • No brightening of the starlight has been detected, as this allegedly huge"cloud" orbits behind the star and should reflect light to us. Shouldn't those huge icy comet clouds reflect some starlight?

  • Jupiter is about as large as a planet can get, even with 10+ times more mass, its volume would not increase by much. Gas giants differ much more in mass than in volume. An object 20 or 200 times more massive than Jupiter would be a roughly Jupiter sized red dwarf star, and that is not what has been observed at "Tabby's star".

The anomalies correlate strictly with the telescope's orbital period and orientation and are obviously a man made artefact because of some unforeseen malfunction of the instrument, nothing astrophysical is involved.

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  • $\begingroup$ I must say that I am not the final authority in this subject. I'm, I hope, a healthy sceptic. There can be good arguments for an astrophysical explanation which have yet escaped my amateur interest. $\endgroup$ – LocalFluff Jan 24 '16 at 14:44
  • $\begingroup$ Thanks for the answer, some very good points you made regarding the reflection of the stars light. I do wonder if the telescopes operators would have looked into instrument malfunction already though. If it caused by some celestial body, I wonder if it is maybe some body or process with which we are not yet familiar. $\endgroup$ – 3therk1ll Jan 24 '16 at 15:29
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    $\begingroup$ Maybe the operators have looked into it. It is just not mentioned in that now infamous paper, anything about how the anomalies are coordinated with the orbit and orientation of the telescope. Instrument malfunction was actually provided for to begin with, and these anomalies were automatically disqualified because they are way beyond any expectation. Only later, by manually looking at the light curve, did this idea occur. Still, it bewilders me how the obvious periodicity aligned with the orbital period of the telescope has escaped the whole idea of using human eyes instead of algorithms. $\endgroup$ – LocalFluff Jan 24 '16 at 15:50
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    $\begingroup$ I see your answer with skepticism. Why would the telescope malfunction with only this particular star when it observes so many of them simultaneously and none of featutres something like this? Further, wikipedia says that somebody discovered that this star dimmed 20% from 1890 to 1989, which is unexpected. $\endgroup$ – Victor Stafusa Jan 24 '16 at 21:30
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    $\begingroup$ @VictorStafusa I did start a question about it here. Observations which correlate better with the telescope's orbit around the Sun than with an astrophysically unique star 1,000+ light years away, is intuitively suspicious to my mind. But I'm not an insider. $\endgroup$ – LocalFluff Jan 28 '16 at 18:39
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There are some theories to explain that. The following explanations, I took from wikipeda's article.

  1. The star has a small companion red dwarf which just crossed its Oort cloud equivalent (at 885 UA). A passing star this close would surely cause havoc and serious disturbances to comets' orbits. This could result in a swarm of comets being thrown into the inner stellar system at once in highly excentric orbits. However, there are severe doubts about this.

  2. It was also proposed that a planet with a very big ring system transits the star (or perhaps, nearly misses and just part of the rings transit the star). This is not unprecedent, and was already seen with another star.

  3. Astronomer Jason Wright suggested that the star might be younger than it seems and it is still coalescing material around it.

  4. Astronomer Bradley Schaefer presented just a few days ago (2016-01-13) a study where he concludes that the star dimmed roughly 20% from 1890 to 1989, and that this is unprecedent for a F-type star. So, there could be still more weird things going on than previously thought.

  5. NASA Infrared Telescope Facility found similiarities with another star, Eta Corvi, which is undergoing a Late Heavy Bombardment.

Wikipedia's article also cites another possibility (which took some headlines around the world). But this is just some (unfortunately notable) sensacionalistic (un|pseudo)jornalistic claim that nobody can take seriously:

  1. There is an advanced alien civilization building a giant device like a Dyson Sphere or something similarly big.

LocalFluff posted an answer suggesting another possibility:

  1. The anomalies correlate strictly with the telescope's orbital period and orientation and are obviously a man made artefact because of some unforeseen malfunction of the instrument, nothing astrophysical is involved.

So, the conclusion (at least my conclusion) is that we simply don't know yet what is happening and we need many follow up observations which will likely tell us a lot. Specially somewhere around May of 2017, when it is predicted that the strange megastructure transit should happen again.

I personally would guess that the close encounter with the red dwarf triggered a Late Heavy Bombardment. But this is only a guess from mine and I have no way to provide evidence for it.

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  • $\begingroup$ I think that there are severe problems with the three first of your listed proposals: 1) That there's no IR emissions as would be expected from any small particles. 2) Nor any brightening of the star as that cloud of gas, dust, asteroids, comets or superstructure passes on the other side of the star and reflects its light, as observed with some common planets. And covering 22% of an F-star in a way which the light curve reveals is not consistent with any kind of transit, not even with one Hell of a late bombardment. It either needs aliens or a (slightly) malfunctioning great space telescope. $\endgroup$ – LocalFluff Jan 28 '16 at 9:28
  • $\begingroup$ @LocalFluff In fact those proposals are not mine, I just compiled them based on the wikipedia's article. I decided to omit the "aliens building a Dyson sphere" because albeit being of (pseudo-)jornalistic relevance, nobody considers this seriously (and it is only a sensacionalistic idea). About your telescope malfunction idea, I commented that in your answer. $\endgroup$ – Victor Stafusa Jan 28 '16 at 15:08
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I've been pondering the dimming of this star for a couple months now and have come up with a plausible explanation. The dimming is probably caused by a very dim companion dwarf star in a highly elliptical orbit where its closest approach to KIC8462852 (Tabby's Star) is on, or near, the same path as our line of sight. The gravitational pull from the dwarf would create tidal forces on Tabby's star causing it to bulge in the same way our moon causes the oceans to bulge.
As is commonly known, stars that spin very fast tend to bulge at their equators due to centripetal force and this results in decreased pressure within the star.. this decreased pressure slows down the nuclear fusion causing a dimming effect at the equator. Consequently, as the bulging equator causes the north and south poles to get closer together, they get brighter due to the increased pressure because they are closer to the stars core. So with Tabby's star, as the dim dwarf is at its closest approach, it causes Tabby's star to bulge a bit.. that bulging causes nuclear fusion to slow, causing a dimming affect.. combine this with the dwarf star blocking some of the light itself and I think we could account for the 20% reduction. The next mystery that has to be explained is the 100 year dimming of the star.. I believe that as the two companions interact with each other, material from each is probably ejected and probably stays within a close orbit of the main star. This would account for a pattern of continuous dimming as this material built up on each pass. This would also account for why we don't see any infrared signature because the ejected materials orbit is too close to distinguish it from the main star.
If I'm right, our telescopes should be able to see the main star wobble back and forth (alot) as the dwarf rapidly transits from its approach on one side of the star, then to the other side on during its departure.

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  • $\begingroup$ That's a really interesting theory. Is it being explored elsewhere? $\endgroup$ – 3therk1ll Jan 24 '16 at 22:18
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    $\begingroup$ Not that I know of.. I'm just an armchair wannabee with a really good imagination for how things work. $\endgroup$ – Murphy Jan 24 '16 at 22:20
  • $\begingroup$ If companions interfere with the fusion process of stars then exoplanetists have some extra headache, as if sunspots wasn't enough. The problem with even that hypothesis in this case is that the anomaly is not transiting. That is immediately seen from the light curve and together with the 22% dip, that's what the big fuzz is all about. There are, as I see it, three regular episodes of increasing disturbances. The final episode is very irregular. Nothing in orbit around that star could match it. But the three episodes match the telescope's orientation and orbit around the Sun. $\endgroup$ – LocalFluff Jan 28 '16 at 9:36

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