A KIC 8462852 (dipping again in March 2018)

[Bandersnatch]

Still the author is assuming the objects are in orbit. However unlikely the relative speeds may be, can we confidently rule out the possibility that the objects are in interstellar space?
What other crazy ideas are we considering here? Orbital comets that massively occult a star that's bigger than the sun and an alien Dyson sphere.

The problem with an interstellar cloud of debris is that you need it to maintain sufficient spread for the required occultation, without collapsing under its own gravity to form a more compact object.

 

[inuk2600]

The problem with an interstellar cloud of debris is that you need it to maintain sufficient spread for the required occultation, without collapsing under its own gravity to form a more compact object.

Is it really a problem or a failure of imagination?

 

[Ernest S Walton]

Still the author is assuming the objects are in orbit. However unlikely the relative speeds may be, can we confidently rule out the possibility that the objects are in interstellar space?

The authors clearly rule it out, saying "...clumps that are too distant move too slowly across the stellar disk to explain the observed duration regardless of their size; e.g., a 3-day duration dip cannot arise from a clump beyond 15 AU." And they go on to say "... the middle solid line and a depth of = 20% therefore decreases the outer limit on the clump locations mentioned above to closer to 8 AU."

 

[inuk2600]

The authors clearly rule it out, saying "...clumps that are too distant move too slowly across the stellar disk to explain the observed duration regardless of their size; e.g., a 3-day duration dip cannot arise from a clump beyond 15 AU." And they go on to say "... the middle solid line and a depth of = 20% therefore decreases the outer limit on the clump locations mentioned above to closer to 8 AU."

This is true if the objects are in orbit and local to the system. Remember these constraints assume the objects are in orbit.

 

[sophiecentaur]

Remember these constraints assume the objects are in orbit

Do you have any other suggestions?

 

[inuk2600]

Do you have any other suggestions?

That's all I got.

 

[Lanniakea]

Can someone point me towards the mathematics behind estimating the size of an object from the dip in light curve? I read somewhere (I can't remember for the life of me where) that if the object blocking this star was the size of Jupiter, the dip in flux would have been less than 1%. This is a periodic dip of 15-22%, which is insane if correct. Can anyone verify these estimations?

 

[Bandersnatch]

Can someone point me towards the mathematics behind estimating the size of an object from the dip in light curve? I read somewhere (I can't remember for the life of me where) that if the object blocking this star was the size of Jupiter, the dip in flux would have been less than 1%. This is a periodic dip of 15-22%, which is insane if correct. Can anyone verify these estimations?

Since the star and occulting object is so far away, you can assume the light rays coming from the disc of the star to be parallel. The percentage of luminosity dip caused by the occulting object is then just the percentage of the disc of the star that is covered by the object. In other words, the dip is proportional to the ratio of the cross-sectional areas of the object and the star.

You know how Jupiter is roughly 10 times smaller than the Sun by radius? Compare the area of a circle with radius 1/10 R (Jupiter) with the area of a circle with radius R (Sun):
$\frac{A_{planet}}{A_{star}}$
$\frac{\pi (0.1R_{Sun})^2}{\pi R_{Sun}^2}=0.01$
Or 1%. The star being the subject of this discussion is larger than the Sun, so a Jupiter-sized planet would occult less than the 1%. To calculate how much less, do the same calculation as above, only with the radius of the star equal to 1.58 R.

 

[Lanniakea]

Since the star and occulting object is so far away, you can assume the light rays coming from the disc of the star to be parallel. The percentage of luminosity dip caused by the occulting object is then just the percentage of the disc of the star that is covered by the object. In other words, the dip is proportional to the ratio of the cross-sectional areas of the object and the star.

You know how Jupiter is roughly 10 times smaller than the Sun by radius? Compare the area of a circle with radius 1/10 R (Jupiter) with the area of a circle with radius R (Sun):
$\frac{A_{planet}}{A_{star}}$
$\frac{\pi (0.1R_{Sun})^2}{\pi R_{Sun}^2}=0.01$
Or 1%. The star being the subject of this discussion is larger than the Sun, so a Jupiter-sized planet would occult less than the 1%. To calculate how much less, do the same calculation as above, only with the radius of the star equal to 1.58 R.

Thank you! My only question is, how much would the distance from the star contribute? For example let's say Jupiter was orbiting this star at 2 AU away, would it not theoretically block more light from our perspective if it were say 8 AU away? It is established that this object does orbit the star (or else it's an astronomical coincidence) with a period of about 750 days. If this local distance effect is negligible and if I'm doing the maffs correctly, then here are some results:

If the object occulting this star were a sphere with the radius of Jupiter, it would block 0.4% of the incoming light.
If the occulting object is a sphere that blocks between 15% and 22% of the incoming light (as observed), its radius would have to be between 61% and 74% of our sun's radius.
For perspective, TrES-4b is the fourth biggest planet discovered according to wikipedia, and it's radius is about 1.8 that of Jupiter, which gives us very roughly 18% solar radii.

What the hell is that?

 

[newjerseyrunner]

@Lanniakea that's why it's more likely a fairly small object (in terms of mass.) If it were huge, we'd also see the star getting pulled around by it's gravity.

Dense objects like planets have small radii, defuse objects can be much much larger. If you were looking at our solar system, the widest object isn't Jupiter, it's Saturn. A comet approaching the sun's coma also can be significantly wider than Jupiter.

I wonder if a large moon or plutoid being pushed inward could create the affect. What would happen if a fairly large stray object (rogue planet) passed close enough to Jupiter to pull one of it's moon away. Would it act like a short term comet? I imagine if a comet 50 miles across can create a coma thousands of miles across, an icy object 500 miles across could make a mind bogglingly huge coma.

 

[Lanniakea]

@Lanniakea that's why it's more likely a fairly small object (in terms of mass.) If it were huge, we'd also see the star getting pulled around by it's gravity.

Dense objects like planets have small radii, defuse objects can be much much larger. If you were looking at our solar system, the widest object isn't Jupiter, it's Saturn. A comet approaching the sun's coma also can be significantly wider than Jupiter.

I wonder if a large moon or plutoid being pushed inward could create the affect. What would happen if a fairly large stray object (rogue planet) passed close enough to Jupiter to pull one of it's moon away. Would it act like a short term comet? I imagine if a comet 50 miles across can create a coma thousands of miles across, an icy object 500 miles across could make a mind bogglingly huge coma.

The object has a period of about 750 days and the first time it passed it created a 15% dip, and then 750 days later a 22% dip + many smaller dips around this time. I'm by no means an astronomer, but what kind of diffuse object or even pack of comets blocks 61-74% of the sun's radius worth of light at a periodic interval? In the paper they say a broken up exocomet is the most likely scenario of all they considered, and I with my completely unprofessional opinion agree, a broken up/smeared out object seems to be by far the most likely explanation, but 61-74% solar radius? Wow

EDIT: The 4th biggest planet I mentioned is basically a big ball of gas that is speculated to have a huge tail and hilariously low density. I don't see what density has to do with anything here?

 

[Bandersnatch]

My only question is, how much would the distance from the star contribute? For example let's say Jupiter was orbiting this star at 2 AU away, would it not theoretically block more light from our perspective if it were say 8 AU away?

The distance doesn't contribute, because the thing you're looking at is so far away.
If you were to draw light rays coming to your eye from the edges of an object, you'd get something like this:

If you place an object between the source and the observer, how much light reaches the observer will depend on the proportion of the distance between the two lines that the object obscures.

Now imagine the distance d increases to an absurdly large value as compared to the size of the object being observed (here, ~1500 light-years vs 1.58 Sun radii). The angle alpha becomes very small, and the lines of light rays become indistinguishable from parallel on the scale of a stellar system. So whether the object is 1 AU or 1 ly from the star, the distance between the lines of light rays is practically unchanged, and the same amount of light gets blocked.

 

[DaveC426913]

In the paper they say a broken up exocomet is the most likely scenario of all they considered, and I with my completely unprofessional opinion agree, a broken up/smeared out object seems to be by far the most likely explanation, but 61-74% solar radius? Wow

EDIT: The 4th biggest planet I mentioned is basically a big ball of gas that is speculated to have a huge tail and hilariously low density. I don't see what density has to do with anything here?

Well, equivalent to. As a cloud of smaller objects, it won't be and object of that radius.

But even at that, what sized comet would be required to create a debris field that can eclipse 15-22% of a star's light?

Here's a math question for someone:
What is the smallest mass of a cloud that could eclipse 22% of this sun? We'd have to assume some typical shape to the cloud. (If it were a flat disk, seen face-on, like a wall then you'd need far smaller mass, but that's not a plausible shape) And we have no idea how much larger than the star's disc the cloud is. Also donlt know what size particles are.

Let's start with a basic ideal shape. Let's say the cloud is entirely contained within the sun's disc, and let's say the cloud it is spherical. What is the minimum mass of the cloud to occlude 22% of the sun's disc?

 

[Bandersnatch]

Let's start with a basic ideal shape. Let's say the cloud is entirely contained within the sun's disc, and let's say the cloud it is spherical. What is the minimum mass of the cloud to occlude 22% of the sun's disc?

Minimum?
Then you need only one particle in a whole cloud per line of sight. That is, you can compress the spherical cloud of particles into a solid disc, with thickness equal to the size of the particles (assuming they're uniform).

The radius of the disc to obscure 22% of 1.58 solar radii star is about 0.75 solar radii. That gives an area of about 10e18 m^2.
Let's say the size of the dust particles is about 1mm across, and that they are composed of water ice. That gives mass in the ballpark of 10e18 kg, or 1/1000th of Ceres' mass.

 

[DaveC426913]

Minimum?
Then you need only one particle in a whole cloud per line of sight. That is, you can compress the spherical cloud of particles into a solid disc, with thickness equal to the size of the particles (assuming they're uniform).

You stopped reading halfway though, didn't you?

We'd have to assume some typical shape to the cloud. (If it were a flat disk, seen face-on, like a wall then you'd need far smaller mass, but that's not a plausible shape)

 

[Bandersnatch]

You stopped reading halfway though, didn't you?

I kinda did , but then I read again and realized that editing is unnecessary as the answer is still correct - a solid disc is the minimum mass approximation of an obscuring sphere of dust. As was said, you only need one particle in your line of sight, so take that 1-particle-thick disc of dust, and spread it around in 3d - it doesn't matter what gaps are there between particles, as long as you never have two particles in the same line of sight, and you don't spread them beyond the visible disc of the star.

The point being, if you spread it well enough, even a medium-size asteroid-worth of dust is enough to account for the luminosity dip.

Or to put it another way, if you start with a fully-compacted object of mass m, unbind it, and start spreading it around in a spherical fashion, at some point you will have spread it to the extent where the separation between particles comprising the cloud is sufficiently large to avoid more than one particle per line of sight. That's the maximum the mass m can block of the background object, and it's the same as if you just made a solid disc of the same mass.

 

[Lanniakea]

The distance doesn't contribute, because the thing you're looking at is so far away.
If you were to draw light rays coming to your eye from the edges of an object, you'd get something like this:
View attachment 90551
If you place an object between the source and the observer, how much light reaches the observer will depend on the proportion of the distance between the two lines that the object obscures.

Now imagine the distance d increases to an absurdly large value as compared to the size of the object being observed (here, ~1500 light-years vs 1.58 Sun radii). The angle alpha becomes very small, and the lines of light rays become indistinguishable from parallel on the scale of a stellar system. So whether the object is 1 AU or 1 ly from the star, the distance between the lines of light rays is practically unchanged, and the same amount of light gets blocked.

Thank you so much for this, when you explain it like that it becomes almost obvious!

They talk about about a nearby star within about 1000AU passing by that could of in theory disturbed the star's oort cloud in a way that sent a massive cloud of fragments that somehow ended up in an orbit in our line of sight. And this is as far as I know the most logical explanation. But that has to be one helluva cloud to block so much light... Is it reasonable for it to stay coalesced like this (at such a scale) and not give off a detectable IR signal?

Also I haven't seen much light curves like this before, but can dusty/particulate masses create such sharp and well defined dips during transit?

Ahh why did Kepler have to not work in April, this is like an itch I can't scratch. x)
Maybe aliens are decommissioning a very large ice skating rink?

 

[DaveC426913]

I kinda did , but then I read again and realized that editing is unnecessary as the answer is still correct

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.)

 

[newjerseyrunner]

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.)

Ignorant question: what is a sol? A solar diameter?

I have a question: how does a big planet migrate inward? I know that many of the first exoplanets discovered were gas giants orbiting very closely to their star, to close to have formed there. Do they migrate in slowly or does it happen in a few well timed gravitational tugs? If gas giant with icy moons migrates inwards, wouldn't all of those moon start to sublimate all at once and produce a monstrous cloud / ring system? If the planet started out on it's side like Uranus, wouldn't it create a flat disc perpendicular to the planet's orbit?

 

[DaveC426913]

Ignorant question: what is a sol? A solar diameter?

Simpler. A Sol is simply our sun.
So a sphere of diameter 1.58 Sols is a sphere of diameter 1.58x our sun's.

I have a question: how does a big planet migrate inward? I know that many of the first exoplanets discovered were gas giants orbiting very closely to their star, to close to have formed there. Do they migrate in slowly or does it happen in a few well timed gravitational tugs? If gas giant with icy moons migrates inwards, wouldn't all of those moon start to sublimate all at once and produce a monstrous cloud / ring system? If the planet started out on it's side like Uranus, wouldn't it create a flat disc perpendicular to the planet's orbit?

Pretty sure migration happens over astronomical times scales, i.e. tens of millions of years.

No lunar orbit can be maintained at any near distance from the star. (eg. Mercury and Venus have no moons) .
If the planet and moons migrated inward, the moons would form a ring around the star, in the same plane and orbit as the planet.

 

[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.