A KIC 8462852 (dipping again in March 2018)

[Artribution]

You're still missing the point. We have to assume a plausible shape to the dust cloud. Flat discs (whose plane is tangential to the star) are impossible, and no such shape will give us any first order approximation of the mass required. Reject it.

Let's assume a spherical cloud. So a sphere of diameter 1.58 Sols. (This too is not a likely shape, but it'll be a lot closer.)

It seems a disintegrating planet shouldn't create a spherical cloud, though. It should be a long, diffuse trailing cloud - a ring fragment. Like when moons and asteroids disintegrate around planets. You get a ring of debris, not a spherical cloud.

On the other hand, what if the disintegrating planet has moons that survive? Then they could act like shepherd moons, distorting or constraining the shape of the cloud between them. Or they would begin gravitating toward each other, pulling a portion of the cloud into a blob that will eventually form a new planet.

For that matter, could this just be a planet that hasn't finished forming yet?

 

[Bandersnatch]

You're still missing the point. We have to assume a plausible shape to the dust cloud. Flat discs (whose plane is tangential to the star) are impossible, and no such shape will give us any first order approximation of the mass required. Reject it.

Let's assume a spherical cloud. So a sphere of diameter 1.58 Sols. (This too is not a likely shape, but it'll be a lot closer.)

I think you might be missing the point, though. I did not say that the cloud is shaped like a disc. What I was saying, is that a maximally-diffuse spherical cloud obscures as much light as a compact disc of the same mass.
If, for a given luminosity dip, you assume a solid sphere on one end, it'll provide you with the maximum mass boundary. If, on the other end, you assume a sphere so diffuse that no two particles are on the same line of sight, you get the minimum mass boundary (for spherical distributions).
It might turn out that the maximally-diffuse cloud would have to be larger than the disc of the star, which would provide a correction to the minimum mass.
In any case the actual cloud will be somewhere in-between these two, but where exactly would have to be deduced from the shape of the curve, which is something I've no idea how to do.

 

[newjerseyrunner]

It seems a disintegrating planet shouldn't create a spherical cloud, though. It should be a long, diffuse trailing cloud - a ring fragment. Like when moons and asteroids disintegrate around planets. You get a ring of debris, not a spherical cloud.

On the other hand, what if the disintegrating planet has moons that survive? Then they could act like shepherd moons, distorting or constraining the shape of the cloud between them. Or they would begin gravitating toward each other, pulling a portion of the cloud into a blob that will eventually form a new planet.

For that matter, could this just be a planet that hasn't finished forming yet?

My understanding is that the object has to be cold, and can not have resulted from a planetary catastrophe.

 

[DaveC426913]

It seems a disintegrating planet shouldn't create a spherical cloud, though. It should be a long, diffuse trailing cloud - a ring fragment. Like when moons and asteroids disintegrate around planets. You get a ring of debris, not a spherical cloud.

Agreed, but we've no way of determining that.

All I'm attempting to do is determine the lower limit on the mass of a cloud needed to obscure the star.
If that lower limit is, like, five times the mass of Jupiter, then we've got a big problem with the 'comet fragments' theory.

 

[DaveC426913]

I think you might be missing the point, though. I did not say that the cloud is shaped like a disc. What I was saying, is that a maximally-diffuse spherical cloud obscures as much light as a compact disc of the same mass.
If, for a given luminosity dip, you assume a solid sphere on one end, it'll provide you with the maximum mass boundary. If, on the other end, you assume a sphere so diffuse that no two particles are on the same line of sight, you get the minimum mass boundary (for spherical distributions).
It might turn out that the maximally-diffuse cloud would have to be larger than the disc of the star, which would provide a correction to the minimum mass.
In any case the actual cloud will be somewhere in-between these two, but where exactly would have to be deduced from the shape of the curve, which is something I've no idea how to do.

Hm. I see your point.

I was of the mind that a sphere would result in a significant overlap of particles, meaning we could calculate a mass.

So it comes down to the size of the particles. Which is unfortunate, because it mean there is no lower limit to the mass. A disc of large boulders obscuring 20% will mass much more than a disc of dust grains obscuring 20%. So the minimum mass is directly proportional to the size of the particles.

 

[newjerseyrunner]

What type of technology is required for us to figure out what the object is made out of? Isn't it possible to take spectral readings from planets around other stars? If it's diffuse, some light would shine through and allow us to determine what it is? If the most likely candidate is water ice, shouldn't it be fairly easy to check?

 

[Artribution]

I noticed a couple of things about that light curve. First: it's not symmetrical. One side is steeper than the other. Second: It's diffuse on the sides but sharp in the middle. That's the opposite of what an exoplanet transit tends to look like:

In Photoshop, I converted the object's light curve into a gradient curve:

It's not exact, but it gives a rough approximation of what the light curve represents in visual terms:

​

Debris cloud? Or ships orbiting alongside the ringworld?

What type of technology is required for us to figure out what the object is made out of? Isn't it possible to take spectral readings from planets around other stars? If it's diffuse, some light would shine through and allow us to determine what it is? If the most likely candidate is water ice, shouldn't it be fairly easy to check?

I don't know, but if it can't be observed directly, then it should be possible to narrow down the possibilities using computer simulations.

 

[DaveC426913]

I don't know, but if it can't be observed directly, then it should be possible to narrow down the possibilities using computer simulations.​

Pretty sure NJR was thinking of chemical spectro analysis.

 

[DaveC426913]

I noticed a couple of things about that light curve. First: it's not symmetrical. One side is steeper than the other. Second: It's diffuse on the sides but sharp in the middle. That's the opposite of what an exoplanet transit tends to look like:

It's been noted that the curve is not symmetrical, but what do you mean by diffuse on the sides?
Those graphs are far too low-rez to interpolate what the slopes are doing.

 

[Bandersnatch]

The gradual sloping over the span of many days is indicative of an extended coma (or a diffuse cloud of debris/whatever), and that the curve slopes less sharply on one side indicates a tail-like structure. In the case of the transit around day 790 the slope indicates a tail in the prograde direction.
This was also discussed in the paper.

 

[Artribution]

It's been noted that the curve is not symmetrical, but what do you mean by diffuse on the sides?

I mean a transiting exoplanet tends to produce a light curve that looks like this:

A sudden, precipitous ingress and egress leveling out to become a flatter middle section - because the planet is a single mass, and it's either "all there" or all not.

The light curves from KIC 8462852 are the opposite: a smooth ingress and egress that instead of leveling out, drop down into a sharp point.

The shape suggests an object surrounded by a more diffuse cloud of matter, which is what it looks like in the gradient curves.

TLDR: What Bandersnatch said.

 

[inuk2600]

In Photoshop, I converted the object's light curve into a gradient curve:

It's not exact, but it gives a rough approximation of what the light curve represents in visual terms:

​

Debris cloud? Or ships orbiting alongside the ringworld?

I see, so the leading edge is more diffuse than the trailing edge? The gradient has a very comet like feel to it indeed.

 

[newjerseyrunner]

Has any comet we've seen in our solar system created comas anywhere near that size?

Looking at the size of the star and the length of the orbit, it's right in the habitable zone right? Could a captured exoplanet make sense, or a moon that got knocked off of a bigger planet? An icy moon falling towards the inner system would act like a comet right? But it's greater gravity could hold onto it's coma better, and if it had a magnetic core, that could deflect some of the solar wind further reducing the erosion of the coma?

It's red dwarf orbits at about the distance of Plutoids, could it have thrown something the size of Pluto inwards?

 

[DaveC426913]

The light curves from KIC 8462852 are the opposite: a smooth ingress and egress that instead of leveling out, drop down into a sharp point.

The shape suggests an object surrounded by a more diffuse cloud of matter, which is what it looks like in the gradient curves.

OK. I thought you were suggesting the curve itself was diffuse, as in you were seeing detail in it.

 

[Artribution]

I see, so the leading edge is more diffuse than the trailing edge?

I didn't notice that until now, but yeah, it's the leading edge that's longer, not the trailing edge.

I realize it doesn't really mean anything, but just out of curiosity, I made a more mathematically accurate gradient:

And applied a uniform blur:

And some enhancement:

​

 

[RealTwistedTwin]

Are there any measurements of the stars doppler shift? I mean if there is a Dyson sphere orbiting the star it wouldn't really have much impact on the star. But as far as I know all the other explanations require huge amounts of masses orbiting the star, so they would surely leave a hint in the spectrum of the star.

 

[Bandersnatch]

But as far as I know all the other explanations require huge amounts of masses orbiting the star, so they would surely leave a hint in the spectrum of the star.

None of the considered scenarios require a large mass.
All measurements to date, including spectroscopy, are discussed in section 2 of the paper linked to in post #7. There's no indication of a massive companion to the star.

 

[Dotini]

Has any comet we've seen in our solar system created comas anywhere near that size?

A comet coma bigger than the sun. Yes.
http://www.space.com/4643-incredible-comet-bigger-sun.html

 

[jerromyjon]

I made a more mathematically accurate gradient:

That doesn't seem to fit where I'm at in my head. I look at it this way...

It gradually builds up the amount of light it blocks (very slowly, very small amount) then and "BAM" it blocks a huge amount of light for a very brief time and then more abruptly it disappears. like a quickly moving large dark companion with low mass so the star doesn't wobble. Hmm.

What about if the "cloud" is being acted upon by a magnetic field which aligns all the orientation to cause the particles to interfere destructively at a narrow angle to our line of sight?

Or a complex orbit which only passes our line of sight every so many orbits? If there was a huge black companion (dead star) revolving with a bright partner (attracted hydrogen how ever many millions of years later) would we be able to see such a quick orbit? Is there any such cosmological model of such a thing? I'm way out of my league here.

 

[Last_Exile]

Has the possibility of starspots been completely ruled out?
http://blog.planethunters.org/2013/02/11/starspots-and-transits/

 

[mfb]

I finally read the paper, and the comet explanation sounds too reasonable :(. Sure, the size of the dips is massive, but it agrees with all measurements. It is also the explanation with the least promising outlook. There is some chance to see more dips within 1-2 years or in a few decades, but the star could stay without further dips forever now if the orbit is eccentric enough. The infrared emission from the comet fragments is going down fast, so I don't know if other telescopes (in particular, JWST in 2018+) are still sensitive to it.

Is the source data for the measured intensity available somewhere? It would be interesting to compare possible matter distributions to the observed light curve.

@Last Exile: It is ruled out in the paper. In particular, the light curve does not fit to the rotation period.

What about if the "cloud" is being acted upon by a magnetic field which aligns all the orientation to cause the particles to interfere destructively at a narrow angle to our line of sight?

Or a complex orbit which only passes our line of sight every so many orbits? If there was a huge black companion (dead star) revolving with a bright partner (attracted hydrogen how ever many millions of years later) would we be able to see such a quick orbit? Is there any such cosmological model of such a thing? I'm way out of my league here.

That does not make sense.

 

[Artribution]

That doesn't seem to fit where I'm at in my head.

It is accurate, though. The gradient spans the width of the image. You may need to adjust your monitor's brightness settings or zoom in closely to see it.

 

[DaveC426913]

Has the possibility of starspots been completely ruled out?
http://blog.planethunters.org/2013/02/11/starspots-and-transits/

I don't think starpots were ever a serious consideration.
The periocity of the observed transits are on the order of 750 days.
The rotational periocity of the star is on the order of 20 hours.

 

[Lanniakea]

I finally read the paper, and the comet explanation sounds too reasonable :(. Sure, the size of the dips is massive, but it agrees with all measurements. It is also the explanation with the least promising outlook. There is some chance to see more dips within 1-2 years or in a few decades, but the star could stay without further dips forever now if the orbit is eccentric enough. The infrared emission from the comet fragments is going down fast, so I don't know if other telescopes (in particular, JWST in 2018+) are still sensitive to it.

Is the source data for the measured intensity available somewhere? It would be interesting to compare possible matter distributions to the observed light curve.

@Last Exile: It is ruled out in the paper. In particular, the light curve does not fit to the rotation period.

That does not make sense.

We missed a transit in April, when Kepler was nonfunctional. The next one is predicted to be roughly in May 2017. What's odd about the curves is that the first transit is so smooth and well defined, while the second one is so chaotically distributed. The two small dips at the beginning of the graph are a bit odd too. So from my understanding, the interesting bit is that a well defined object became diffuse and chaotically distributed, with no apparent IR signature. Then again, the universe is kinda large, you'd expect some coincidences here and there. But yeah comets from outside the system or the oort cloud make by far the most sense. Unless the ATA has something to tell us, I guess we're going to have to wait till 2017 to find out. ):

 

[mfb]

A possible transit - for something in a 750-day orbit. If something is in such an orbit, then we'll see it again. That is unlikely, given the analysis in the paper.

With a broken up comet, all dips come from different objects so their different structure is not surprising.

 

[Vanadium 50]

If you break up a comet, the fragments need to be pretty small to get enough surface area to block out a substantial fraction of a star's light. Somewhere in the 100um to 1mm ballpark.

 

[DaveC426913]

Well comet Holmes might have done the trick.

To-scale comparison:

https://en.wikipedia.org/wiki/Comet_Holmes
http://www.space.com/4643-incredible...igger-sun.html

 

[Vanadium 50]

It's not enough to make the extent large. One also needs to make it dark. You can't get it dark enough with only billions or trillions of particles. You need a lot, and they need to be really, really small.

 

[Lanniakea]

Well comet Holmes might have done the trick.

To-scale comparison:

https://en.wikipedia.org/wiki/Comet_Holmes
http://www.space.com/4643-incredible...igger-sun.html

So it is reasonable to believe that the nearby passing star could've directed a comet from it's own system or the oort cloud (origin doesn't matter too much I suppose) towards Tabby's star, which is when it created a coma as it got close, then this coma was shifted around by gravitational/collision events and that's why it looks so chaotic in the second transit? This is pretty much the most reasonable scenario I can think of.

 

[DaveC426913]

It's not enough to make the extent large. One also needs to make it dark. You can't get it dark enough with only billions or trillions of particles. You need a lot, and they need to be really, really small.

Why do they need to be small?

Is it because, for a given mass, the smaller the particle size the better the light-blocking?

 

[Vanadium 50]

The total surface area needs to be comparable to the star's area to block a significant amount of its light. If you take something with a comet's mass, to get enough area drives you to break it up into 100um-1mm sized objects.

 

[nikkkom]

That lightcurve looks very similar (except for it's magnitude) to the one produced by KIC12557548

The difference is, KIC12557548 is far from certain to be periodic at all, and it's not sub-24 hour transit for sure.

(My own hunch is that KIC12557548 dimming events are not transits at all.)

 

[nikkkom]

>>Has the possibility of starspots been completely ruled out?
>>http://blog.planethunters.org/2013/02/11/starspots-and-transits/

@Last Exile: It is ruled out in the paper. In particular, the light curve does not fit to the rotation period.

These may be starspots of a type we never seen before. For example, starspots which are pole centered.

 

[mfb]

So it is reasonable to believe that the nearby passing star could've directed a comet from it's own system or the oort cloud (origin doesn't matter too much I suppose) towards Tabby's star, which is when it created a coma as it got close, then this coma was shifted around by gravitational/collision events and that's why it looks so chaotic in the second transit? This is pretty much the most reasonable scenario I can think of.

The paper authors suggest that all different transits are different fragments. No orbit, and chaos because every event is different.

These may be starspots of a type we never seen before. For example, starspots which are pole centered.

You have to cover a large fraction of the whole star with spots to get 20% intensity reduction. Also, why should they be exactly pole-centered?

 

[nikkkom]

You have to cover a large fraction of the whole star with spots to get 20% intensity reduction. Also, why should they be exactly pole-centered?

"Why pole centered?", we do see pole-centered "atmospheric" phenomena, such as Saturn's polar hexagon.

Since Kepler did not see such dimming events on any other star, this star may exhibit some rare phenomenon. Maybe its starspots appear much rarer than on the Sun, but when they do, they cover nearly a quarter of poleward surface.

 

[newjerseyrunner]

"Why pole centered?", we do see pole-centered "atmospheric" phenomena, such as Saturn's polar hexagon.

Since Kepler did not see such dimming events on any other star, this star may exhibit some rare phenomenon. Maybe its starspots appear much rarer than on the Sun, but when they do, they cover nearly a quarter of poleward surface.

Wouldn't a gigantic starspot create a huge amount of infrared? As far as I understand, starspots are formed when magnetic loops kink so badly that they extend beyond the surface. In order to make a huge sunspot, wouldn't you require an insanely huge magnetic loop and create a lot of fast moving, extremely hot plasma that would glow like hell in IR? Lots of objects create huge magnetic vortexes at their poles (pulsars, quasars, black holes...) but they're all huge.

Are there any models for how a star might behave it for some reason it had an inordinate amount of iron in it's core? The amount of iron required to create magnetic fields of that strength?

 

[nikkkom]

Wouldn't a gigantic starspot create a huge amount of infrared?

If radiation spectrum is blackbody, then lowering of temperature would not increase any part of the spectrum. The peak moves to redder wavelenghts, yes, but intensity at any particular frequency still falls, it does not increase. See at 7:00 in this video:

 

[nikkkom]

Are there any models for how a star might behave it for some reason it had an inordinate amount of iron in it's core? The amount of iron required to create magnetic fields of that strength?

At those temps, iron is not ferromagnetic :D
As a rule of thumb, for stronger magnetic fields of stellar (and planetary) objects, you need faster rotation. Incidentally, this star rotates faster than one revolution per day.

 

[newjerseyrunner]

At those temps, iron is not ferromagnetic :D
As a rule of thumb, for stronger magnetic fields of stellar (and planetary) objects, you need faster rotation. Incidentally, this star rotates faster than one revolution per day.

You're right, I forgot that in objects like that its metallic hydrogen that makes the magnetic fields, not iron. One revolution a day is not that fast.

If radiation spectrum is blackbody, then lowering of temperature would not increase any part of the spectrum. The peak moves to redder wavelenghts, yes, but intensity at any particular frequency still falls, it does not increase. See at 7:00 in this video:

I'm not referring to the spectrum of the star itself, I'm saying that starspots are caused by massive magnetic loops that break the surface. Along those loops plasma races around at incredible speeds. Once those loops unkink, all of that plasma gets released from the magnetic clutches of the star and gets ejected out into space (a solar flare.) If this star is constantly having magnetic storms so fierce that starspots can dim it's light output by 20%, it should be sitting in a vast cloud of hot gas, similar to if two planets collided with each other. Wouldn't it? I'm saying that you would be able to detect all of that plasma being thrown off of the star in the IR.

 

[DaveC426913]

These may be starspots of a type we never seen before. For example, starspots which are pole centered.

Unfortunately, that's drifting into an area where
a] it requires the invocation of an unprecedented phenomenon - and even granting that -
b] it still requires some tortured explanations (such as smoothness and periocity) in even make it fit our fantastic phenomenon.

With that, all bets are off. We wouldn't go much farther off to posit billions of pixies holding hands in a maypole dance.

 

[nikkkom]

Unfortunately, that's drifting into an area where
a] it requires the invocation of an unprecedented phenomenon - and even granting that -
b] it still requires some tortured explanations (such as smoothness and periocity) in even make it fit our fantastic phenomenon.

The point is, I don't see any periodicity of the dimming events in the data.

There was one nearly 20% dimming event, then some 700 days later a group of three other dimming events first of which was even deeper. Each of four events has a different shape.

That's why I thought "these are probably not transits at all" and came up with my pet theory.

 

[DaveC426913]

The point is, I don't see any periodicity of the dimming events in the data.

There was one nearly 20% dimming event, then some 700 days later a group of three other dimming events first of which was even deeper. Each of four events has a different shape.

OK, starspots have the distinction of not needing to have a highly-constrained periocity. I'll give it that.

 

[DaveC426913]

Point of order:
Everywhere I've used the word periocity, you should be hearing periodicity in your head.

 

[Michael Lazich]

Some really intriguing light curves here. Read the article for some explanation.

http://www.slate.com/blogs/bad_astr...ge_dips_in_brightness_are_a_bit_baffling.html

Look at the smooth curve lower left. That has got to be a single body transit. Multiple bodies couldn't make such a smooth curve. Yet that body results in a 15% drop in the light curve!
And it's cold, so not a companion star.

I don't see how exo-comet fragments can explain this.

Black dwarf?

I've been struck how the lower left curve looks like what could be produced by a spinning disk or other object...

Black Monolith anyone...? ;)

 

[mfb]

I've been struck how the lower left curve looks like what could be produced by a spinning disk or other object...

How?

 

[rootone]

Maybe a really massive companion planet which itself has several very large moons orbiting it?

 

[Michael Lazich]

How?

Actually, the cross sectional area of a spinning disk could be said to have the "general" shape of the light curve, and that for only a single rotation.

The light curve from a star with such a spun disk in front of it would actually look like the inverse of what was observed from KIC 8462852.

I just calculated the cross section of a spinning disk with the dimensions such that, at full occultation, the light from the star would be around 84% of its maximum value; as it rotates through 180 degrees, the occulting area varies as cosine of the rotation angle and you get the curves below:

Of course, the actual observations are asymmetrical and are the *inverse* of the light curve that would be produced under the assumptions above.

Just thought it was interesting.

 

[mfb]

I don't see where you imagine a disk and how spinning that disk would be relevant.

 

[Michael Lazich]

I don't see where you imagine a disk and how spinning that disk would be relevant.

 

[newjerseyrunner]

That looks like you're describing a flipped coin. Discs don't spin that way, there is no physical way for anything like that to naturally form. Discs spin along their plane, that's what makes them discs in the first place: angular momentum.