A KIC 8462852 (dipping again in March 2018)

[Murphy625]

Hello,
This is my first post here. I have no idea what thread level to use so I just picked the middle one.
I'm hoping someone can tell me if my theory on Tabby's star ( KIC 8462852) is plausible or not.

Since its discovery, there's been much hoopla over the strange behavior of this star. Just last week, an astronomer (Bradley Schaefer?) inspected old photos of the star dating back to the 1890's and discovered that the star has been dimming for over 100 years. Since that, no new theories have come out.

Alien Megastructure? That would be cool.. but not probable. They've pretty much debunked the comet or gas cloud theories and no one has come up with anything since. So, here goes my 2 cents.. I'm hoping someone here can debunk this for me. We have to explain the periodic and regular 20% drops in luminosity (Flux?) and the 100 year trend of dimming something like 20%.

What if 8462852 was a binary system consisting of one main sequence F star and a dwarf star companion?
If the dwarf star was in a highly elliptical orbit around the main star and at its closest approach, being along our line of sight, was close enough to impart tidal forces on the main star, couldn't that account for what we are seeing?
My theory goes like this: As the dwarf circled around the main star, the gravitational pull of the dwarf would cause the main star to bulge via tidal forces. This in turn would reduce the pressure within the main star and result in decreased nuclear fusion which would cause it to dim on the side facing the dwarf. Could that dimming effect, coupled with the dim dwarf blocking some of the light itself, account for the whopping 20% we are seeing?
Additionally, as the dwarf swung around the main star, wouldn't both stars eject material into space from all that disturbance? That ejected material would build up on each pass of the dwarf and if that material remained in a close orbit around the main star, couldn't that account for the century long dimming trend?

 

[Chronos]

It is doubtful a companion star would affect the fusion rate of a star. Local gravitational effects would overwhelm tidal effects of any companion star unless they were extremely proiximate. A more likely explanation is the primary star is accumulating helium in its outer core. Even this explanation is suspect because helium accumulation typically takes many eons, not centuries, to create noticeable effects.

 

[Murphy625]

It is doubtful a companion star would affect the fusion rate of a star. Local gravitational effects would overwhelm tidal effects of any companion star unless they were extremely proiximate.

Extremely proximate: Like within the orbit of Mercury?? Or are we talking something much closer?
I'm also wondering if it would make any difference that Tabby's star has a rotational period of less than a day.. Wouldn't there already be a bulging equator?

 

[Chronos]

There might be a little bit of centrifugal going on there, but, probably not significant. I would guess any companion would need to be at least as close as mercury to matter much. Ordinarily, you need a contact binary to wreak much havoc on a star.

 

[laner]

I would tend to agree with Chronos. As for the material ejection, I would find it difficult to imagine that you could tidally strip a star without having a controlled mass transfer through a Roche lobe or something, which would more likely be seen between a giant star and a high-mass companion.

Also if your dwarf is passing between the giant and our line-of-sight then you are going to pick up the orbital motions through spectroscopy, and I would assume someone has checked for that.

 

[Murphy625]

Is there anything that would prevent a dwarf star from being within a mercury orbit? Not that I'm aware of.

I looked all over and I can find no information relating to anyone checking to see if this star wobbles. The wobble, or lack of, would most certainly confirm or debunk my idea but I can not find anything on the internet that says the wobble has been measured. And to think of it, why would I? The only time that wobble would be seen is during the 750 day event when the dwarf swings quickly around the main star.

 

[mfb]

Is there anything that would prevent a dwarf star from being within a mercury orbit? Not that I'm aware of.

Nothing, and there are binary stars closer than that.
It leads to massive radial velocity changes within this period. Nothing like that has been observed for the star.
It also cannot explain the slow dimming over the last 100 years, or the light curve of the short dimming events.

 

[newjerseyrunner]

How is interstellar dust observed? Is it possible that the century long dimming is simply because it's moving behind a cloud of dust that's unrelated to the star itself? Would spectral analysis show that? From the wikipedia article, it seems like a swarm of asteroids or comets would account for the short dimming, but not the long ones.

I've read that a massive collision has been ruled out because of the lack of infrared energy, but what about a large object straying close to the Roche limit? Would an object getting torn apart by gravity produce the same infrared energy or no? a 750 day orbit that takes something near or past that limit would be highly elliptical, but I see no reason that it's impossible. I imagine an object close to the limit, but not quite there would slowly break apart and recombine, allowing the dust to slowly build up over a century, as well as produce large cyclical dips.

Most objects that get close to that limit are just torn apart all at once, but I'm curious what would happen if it's in an elliptical orbit and only stays close to that limit for a short time before being flung back out. Especially if it's large enough to put itself back together each pass.

 

[Murphy625]

Nothing, and there are binary stars closer than that.
It leads to massive radial velocity changes within this period. Nothing like that has been observed for the star.
It also cannot explain the slow dimming over the last 100 years, or the light curve of the short dimming events.

Can you point me to a link were they have looked at the radial velocity (the wiggle?) during the periodic dimming events?
Also, while I understand the obvious meaning of the light dimming curves, I am not adapt to reading the finer details of the curves which tell us something about the object(s) that are blocking the light. It would be nice to find some good reading on that.

 

[mfb]

We characterize the object with high-resolution spectroscopy, spectral energy distribution fitting, radial velocity measurements, high-resolution imaging, and Fourier analyses of the Kepler light curve.

Guess where: in the original paper.
Section 2.6 sets explicit limits on close companions. For circular orbits, but the limits would not be that different for eccentric orbits.

 

[Murphy625]

Guess where: in the original paper.
Section 2.6 sets explicit limits on close companions. For circular orbits, but the limits would not be that different for eccentric orbits.

Thank you so much for the link.

 

[mfb]

A new arXiv submission questions the reliability of the old magnitude measurements, they find similar trends for 18 of 28 similar stars.
KIC 8462852 did likely not fade during the last 100 years

Here the original dimming paper as reference
They also checked reference stars, obviously, but maybe not enough?

 

[Bernie G]

Same group too.

Sounds reasonable ... maybe a rocky volcanic planet in an elliptical orbit is being shredded by this star.

 

[Murphy625]

A new arXiv submission questions the reliability of the old magnitude measurements, they find similar trends for 18 of 28 similar stars.
KIC 8462852 did likely not fade during the last 100 years

Here the original dimming paper as reference
They also checked reference stars, obviously, but maybe not enough?

I read that this morning! Looks like I'm just going to have to hold my breath until they figure out if the 100 year trend is valid or not. Thank you.

 

[Chronos]

The photometry artefact explanation is entirely reasonable. It is certainly a challenge to mine much useful data from old photometric plates and the fact that nearly 2/3 of similar stars examined for complarison displayed similar patterns of variability is the stuff of legends. This is a prime example why most scientists are reticent, if not terrified, to announce such odd findings. Nobody wants to make a splash at a conference and be tagged as 'old 8462852'.

 

[Murphy625]

Mr. Schaefer's analysis of plates dating from 1890 to 1989 does not include data after 1989. So where is the data from 1989 to present? That's 26 years of information that no one seems to mention, unless I missed it somewhere.
Shouldn't the last two and a half decades of a century long dimming trend be detectable in the modern data?

 

[Borg]

Mr. Schaefer's analysis of plates dating from 1890 to 1989 does not include data after 1989. So where is the data from 1989 to present? That's 26 years of information that no one seems to mention, unless I missed it somewhere.
Shouldn't the last two and a half decades of a century long dimming trend be detectable in the modern data?

From the second sentence in mfb's link, the analysis was performed against archival photographic plates. I would presume that the data was stored electronically after that.

 

[Murphy625]

From the second sentence in mfb's link, the analysis was performed against archival photographic plates. I would presume that the data was stored electronically after that.

Thank you. I have since learned that the data for the time after 1989 to present showed no gradual long term dimming trend. If Schaefer's analysis was correct, wouldn't we expect to see a continuation of that dimming for the 26 years after his last data point?

 

[Borg]

A newly submitted paper on arxiv - KIC 8462852 Faded Throughout the Kepler Mission.

 

[member 342489]

This seems relevant...

https://carnegiescience.edu/node/2102

 

[newjerseyrunner]

Finally https://www.google.com/amp/s/phys.org/news/2017-01-explanation-alien-megastructure.amp

A new hypothesis is that about 100 years ago a planet took a dive into the star, which caused it to get brighter. Since then, it's been dimming back to its natural state. It also theorizes that the rapid periodic dimming is caused by remnants left after gravity ripped he planet apart.

 

[mfb]

or a large number of smaller objects – such as moon-mass bodies that were about 1 km in diameter. This latter possibility seems more inviting

Edit: Ah, many 1km objects with a total mass similar to the Moon.

Unless KIC 8462852 is an extremely obscure case, TESS in 2018+ and later PLATO (2024+) will find more of them (3 and 6 times the number of observed stars, respectively).

 

[mfb]

It is dimming again!
News article
Blog article

~2% at the time the articles were written. This time, it will get a lot of telescope time to study the transit in as much detail as possible.

 

[Borg]

I can't remember if this has been discussed in this thread but has any consideration been given to the dimming being due to a debris field from two planet-sized bodies that have collided?

 

[mfb]

That is similar to the comet approach, one of the most plausible options. It cannot be in a circular orbit, however, as that would lead to notable infrared emissions and a more periodic transit structure.

 

[nikkkom]

I can't remember if this has been discussed in this thread but has any consideration been given to the dimming being due to a debris field from two planet-sized bodies that have collided?

Just like other many theories, this one has problems.

Why this debris field is not elongating along its orbit, like fragmenting comets do in our system? Why it stays in a "cloud"?
Debris should have lots of dust, why no IR excess is seen?

 

[stefan r]

A new arXiv submission questions the reliability of the old magnitude measurements, they find similar trends for 18 of 28 similar stars.
KIC 8462852 did likely not fade during the last 100 years

Here the original dimming paper as reference
They also checked reference stars, obviously, but maybe not enough?

Dyson spheres growing on 18 out of 28 F type stars.

 

[mfb]

Here is a recent light curve from Tabetha Boyajian‏:

The current Julian Day (at the time of this post) is 2457895.41, or 17.41 on the scale of this plot. 17 on the plot was 10 hours ago.The first dip was seen 3*750 days ago, then three more dips 2*750 days ago, then we don't have much data from 750 days ago so we might have missed events, and now a pattern again. All numbers +- 20 days. Whatever is going on there, it seems to have a 750 day pattern. The next 750 day window is around June 2019.

 

[craigi]

The first dip was seen 3*750 days ago, then three more dips 2*750 days ago, then we don't have much data from 750 days ago so we might have missed events, and now a pattern again. All numbers +- 20 days. Whatever is going on there, it seems to have a 750 day pattern. The next 750 day window is around June 2019.

The nice smooth curve 3x750 days ago looks so dubious now.

 

[newjerseyrunner]

Hasn't it been determined that the most likely scenario is that the star ate a planet? That causes an increase in brightness, which will then, of course, dims back to its original brightness over time. The planet gets ripped apart before being swallowed creating a massive dust cloud.

 

[mfb]

If it is something that breaks apart the structure could get more complex each orbit. We'll see the what happens this time over the next few weeks, and then get more data mid 2019 (in the worst case we don't get any dips, but that would help ruling out models as well).

 

[craigi]

In the graph for the first dimming event, the baseline fluctuation seems to have disappeared completely for the 12 day period. Even the measurement error of about 0.0025 (inferred from the recently posted graph for the current dimming event) isn't apparent in the data. That makes me suspicious of either the data or how it is being represented.

Looking at the curve for the second dimming event, we can see that the graph seems to use a curve interpolation. I wonder how many data points actually contribute to that first curve. A small number over the 12 day period would explain a lot.

Alternatively, if there a large number of data points and the measurement error from the data for the current dimming event is relevant for the first dimming event, then we must ask how those measurements became correlated.

 

[mfb]

In the graph for the first dimming event, the baseline fluctuation seems to have disappeared completely for the 12 day period.

Note the different scales on both axes.
If you scale the noise seen in the large plot to the short period in time but the large range in y, you don't see it any more.
Both curves are probably smoothed (typical raw 15 minute measurements have significantly more noise), but on a scale of an hour or so, not on the scale of days.

 

[ExecNight]

Couldn't it be a pair of black holes between KIC 8462852 and Earth that are orbiting each other. Then this would explain how it regularly (and also irregularly) blocks the light from the star, since one black hole or the other keeps getting in the way while they are orbiting each other.

If these two are near collusion, gravitational waves from these two might be detected?

 

[Bandersnatch]

Then this would explain how it regularly (and also irregularly) blocks the light from the star, since one black hole or the other keeps getting in the way while they are orbiting each other.

No, this is the same scenario as with any other non-black hole body - all closed orbits are periodic, regardless of whether it's a black hole, a planet, or another star. In your sentence the bit in the parentheses does not then follow from the premise.

 

[mfb]

A black hole tends to focus starlight, so we would see more light. The shape of microlensing events is well-known, and looks completely different from what we see here.
Anything not close to the star would need an absurdly precise alignment in terms of velocity in order to stay in the line of sight for years. Whatever it is, it is close to the star.

 

[ExecNight]

A black hole tends to focus starlight, so we would see more light. The shape of microlensing events is well-known, and looks completely different from what we see here.
Anything not close to the star would need an absurdly precise alignment in terms of velocity in order to stay in the line of sight for years. Whatever it is, it is close to the star.

Very interesting indeed.

So facts are;

- Very close to the star.
- Can cause dimming up to %20
- Not a dead star itself, since universe is not old enough.
- Can't be a remnant planet
- Can't be a thick gas cloud.

Then, what is the current theory? Except the *ALIENS* one?

 

[arabianights]

i think it's time to bring in dark matter/dark energy to explain the strange behavior of distant stars.

 

[mfb]

A very messy gas/dust cloud as result of some recent collision process seems to be favored for now. The main components orbit the star every 750 days, and the process is still very dynamic so we see different events each orbit.
It is unclear if that explains the overall dimming, and it is hard to make that consistent with the lack of an infrared excess.

We are back at the baseline luminosity.

 

[Noel]

I'd like to invoke the term "Dark Shadows" as an explanation

 

[stefan r]

i think it's time to bring in dark matter/dark energy to explain the strange behavior of distant stars.

"dark matter" does not effect visible light. Noel nailed it:

I'd like to invoke the term "Dark Shadows" as an explanation

We still need to figure our why the aliens are building dark shadow megastructures. Why are they not radiating infrared or using radio?

Hasn't it been determined that the most likely scenario is that the star ate a planet? That causes an increase in brightness, which will then, of course, dims back to its original brightness over time. The planet gets ripped apart before being swallowed creating a massive dust cloud.

Why would the dust cloud have a 750 day orbital period? What happened to the infra red radiated by the dust? For example, dust around vega is easy to measure.

 

[newjerseyrunner]

Why would the dust cloud have a 750 day orbital period? What happened to the infra red radiated by the dust? For example, dust around vega is easy to measure.

Hmm... 750 days is a little long, I'd expect the dust cloud to be in a tight death spiral. However, I could come up with a scenario: two planet orbit close to each other around that 750 day radius. During a close approach, the planets swing around each other. One gets ripped apart leaving a dust cloud at the right distance and the more massive one gets thrown into the star, causing temporary brightening, which we are now observing the tail end of.

Question though: what would the dust cloud of a such a circumstance look like? Vega's dust ring is 2-3x the distance to Pluto, where this dust cloud is nice and cozy between what would be the orbits of Mars and Jupiter. Vega's dust cloud is also ancient, where if this star ate a planet, it happened in the last hundred years.

 

[stefan r]

Question though: what would the dust cloud of a such a circumstance look like? Vega's dust ring is 2-3x the distance to Pluto, where this dust cloud is nice and cozy between what would be the orbits of Mars and Jupiter. Vega's dust cloud is also ancient, where if this star ate a planet, it happened in the last hundred years.

I was thinking just of the re-emitted infra red. Dust further than pluto radiates in infrared so dust rings near a Mars radius should be blazing. It can not be some of the possible alien megastructures. For some reason they are reflecting light away or perpendicular. Or adsorbing and radiating away/perpendicular.

Hmm... 750 days is a little long, I'd expect the dust cloud to be in a tight death spiral. However, I could come up with a scenario: two planet orbit close to each other around that 750 day radius. During a close approach, the planets swing around each other. One gets ripped apart leaving a dust cloud at the right distance and the more massive one gets thrown into the star, causing temporary brightening, which we are now observing the tail end of.

A comet starts as an icy ball and grows a dust tail when it gets into the inner solar system. The the tail is already too large before finishing half a pass. When comets are completely dusted they turn into continuous long streams. Leonid meteor shower for example. The graph of tabby's star is fairly tight:

[zeit is German for time, normalized flux] The first event starts around 787 and ends 796 with most of it in one day.

I had not noticed the increased flux around day 1550 to 1560.

 

[Mr P]

Wild speculation perhaps but given the habitable zone for an F3 star is around 3au with a period of ~1500 days is it possible that we're looking at 2 structures on roughly opposite sides of the star? That should cancel out the wobble from tidal shifts though why you'd need to do that is another question.

 

[mfb]

The radial velocity is poorly constrained, there could be quite heavy objects orbiting it. But they have to be unusually cold.

 

[newjerseyrunner]

Is there any information about the mass of the orbiting object? Does it have any Doppler affect on the star at all?

Is there still a chance that the dips are coming from the star itself going through cycles from some natural self organized criticality?

 

[Mr P]

Mass of the object(s) appears to be negligible. Ref the original paper section 2.6

 

[craigi]

Again in this representation of the data, the fluctuation disappears almost entirely around day 788 and emerges again around day 795. Then disappears again completely between days 802 and 809.

The magnitude of the fluctuation outside of those ranges is about 0.001 or less, whereas the error bars in the recently posted graph for the current dimming event is about 0.0025.

I can't interpret this as a chance occurrence and since this is the section of data which presents the greatest difficulty for analysis, I think we should understand what's going on with this representation of the data in more detail.

 

[newjerseyrunner]

So everything seems to point to something comet-like. Absolutely huge physically, but almost no mass. A swarm of comets though would not make such a smooth light curve. There is also a known small star nearby that's passed close enough to disrupt objects about the distance of the Oort cloud.

What about an object much larger than a comet? What would happen if you took Pluto and threw it into the orbit of Jupiter? I imagine it'd act like a comet on steroids: the surface nitrogen would sublimate. That'd create a huge, very diffuse atmosphere that'd slowly leak into space. It'd also be cold, and wouldn't create an infrared signature.

 

[mfb]

Again in this representation of the data, the fluctuation disappears almost entirely around day 788 and emerges again around day 795. Then disappears again completely between days 802 and 809.

They don't have to disappear, they are just harder to see. Fluctuations on a constant line (where the curve is going up and down) are easier to see than on a heavily sloped line where you just get slightly smaller and larger first derivatives.