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Thread: Up to 22% Dips Detected in Starlight 1,500 LY Away

  1. #511
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    Quote Originally Posted by kzb View Post
    The BH is physically tiny (tens of km across) compared to the star and it could probably hide within the star, orbiting the core (more likely the core would orbit the BH) over a much longer timescale.
    A black hole that's 10 km across is more than 3 solar masses, where as an F class star is only a little more than 1 solar mass. So a black hole even that big would dominate the dynamics; I don't think there's any way it could remain anything like a stable main sequence star.
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    I understand that planets cannot achieve the physical size needed to explain 22% obstruction of star light. However planets can host rings. A super ring or rings perhaps? Guess its probably already been considered?

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    Quote Originally Posted by Grey View Post
    Sadly, it's not. Say you wanted an image with 10,000 km resolution (so an F class star would be about 180 pixels across, enough to see a moderate amount of detail). We'd need a telescope about 700 km across. Fortunately, you don't actually need a single telescope this big, you could use a network of telescopes linked together. We do this all the time with radio astronomy, but you need to have the telescopes positioned accurately to a precision on the order of the wavelength you're observing in. For radio waves, this isn't too bad, but for visible light, you need to have your telescopes positioned to within a few hundred nanometers. We'd pretty much have to set them up in space (or the atmospheric interference would make it even harder to link the telescopes). So we'd have to launch multiple telescopes each the equivalent of Hubble, and then keep them all positioned relative to each other with astonishing accuracy. We can probably do this someday, but it would take a huge engineering effort.

    Unfortunately, this is even more impractical, given available technology. New Horizons, the fastest probe we've launched, would take about 29 million years to get to KIC 8462852. Even just to get a New Horizons equivalent to Alpha Centauri would take about 78,000 years. Probes work well in the solar system, but we'd need much more advanced propulsion to explore other stars this way. Building a telescope array hundreds of kilometers across in space is actually more practical.
    We wont need to build a big telescope if we can marshal space time curvature at will. If we could do this, we could attune the curvature to form a lens of untold span, to focus light on our modest light collection device. Initial thoughts are that would require a lot of energy to bend space. But what if positive curvature could be created by drawing on the energy of spacetime. That would be like sitting down to a two courses free lunch. Any scifi writers paying attention?

    Or perhaps place a camera in orbit around a BH, looking through the spacetime lens created by the BH. Is there a theoretical point near a BH where light could be harvested for this purpose?

    Imagine what we could see, theoretical resolutions? Black holes, eyes to the universe........
    Last edited by Questing1; 2016-Aug-18 at 03:55 AM.

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    Wasn't there speculation at one time that a black hole in the sun would explain both ice ages and the old solar neutrino problem?

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    Quote Originally Posted by Grey View Post
    A black hole that's 10 km across is more than 3 solar masses, where as an F class star is only a little more than 1 solar mass. So a black hole even that big would dominate the dynamics; I don't think there's any way it could remain anything like a stable main sequence star.
    Completely agree. The discussion was about how fast the BH would eat up the star.

    We need models as to what would actually happen if a stellar-mass BH was present within the star (and in different combinations of mass and depth within the star). Then ascertain if the observations are consistent with any of those models.

    My feeling (and its only that) is it is not possible to reconcile any such model with the observations. The same goes if you substitute a neutron star for the BH.

    There is a more prosaic and fairly boring explanation being proposed: this star is reaching the end of its main-sequence lifespan. Models of F-stars at this stage in their lives show they are very convective, and their output is thus unstable. It's as simple as that. We just happen to have caught this star during a very short intermediate stage, where it is beginning the process of leaving the main sequence.

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    Quote Originally Posted by kzb View Post
    We need models as to what would actually happen if a stellar-mass BH was present within the star (and in different combinations of mass and depth within the star). Then ascertain if the observations are consistent with any of those models.
    What about sub-stellar black holes? If there even is such a thing, of course.
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    Quote Originally Posted by Noclevername View Post
    What about sub-stellar black holes? If there even is such a thing, of course.
    They're certainly possible, although there doesn't seem to be a current way of their forming. A black hole with a mass of about 10^11 kg has a life exceeding the the life of the Universe.
    Last edited by swampyankee; 2016-Aug-18 at 01:39 PM.
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  8. #518
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    Quote Originally Posted by Noclevername View Post
    What about sub-stellar black holes? If there even is such a thing, of course.
    My feeling* is still that, while an extremely small black hole might in principle hang around inside a star without disrupting it much, and could be sufficiently small to not grow too quickly even in the extremely dense interior of a star, it would be too small to cause sudden drops of 22% in luminosity. And a black hole that is large enough to cause that large of a drop would have to be a significant fraction of the mass of the star itself, and would thus quickly disrupt it. Even if it doesn't turn the whole star into an accretion disk overnight, there's no way the star goes back to just being an ordinary main sequence F class star.



    * And I'll admit that this is just a feeling. I haven't tried to model it. But I think my position is reasonable.
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    Okay, so here's an attempt to put some numbers on this. The core of the Sun (close enough to an F class star for our purposes here, just trying to get an order of magnitude; an F class star actually has about 1.1 solar masses, so it would be a little bigger) extends to about 0.2 solar radii, and has about 0.34 solar masses. Let's say a substellar black hole is orbiting right at the edge of the core. Orbital velocity will be about 570 km/s. If our black hole has a mass of 0.01 solar masses, its radius is about 30 meters. The gravity of the stellar core is about 60 g; at about 47,000 km from the black hole, the black hole's gravity exceeds this. That means anything within about 47,000 km will be more strongly attracted to the black hole than to the core of the star. Freefall time from this distance would be about 300 seconds, so gas flows in pretty fast, although of course it would be slower because of all the other mass trying to get in. But remember that unlike the stellar core, where the pressure increases as more material accumulates, material that flows into the black hole doesn't provide any sort of outward balancing force as this process continues. Instead, it just increases the gravity of the black hole.

    Still, let's look at a smaller radius of 25,000 km around the black hole instead. At this range, the gravity is about 216 g, so it pretty much swamps the gravity of the stellar core, and freefall time is now down to 120 seconds. Density of the stellar core is about 150 g/cm3. If we say the black hole accumulates all the mass in this range, then in a single orbit (taking about 1500 seconds), the black hole will sweep up something like 2.5 x 1029 kg of stellar material, which is about 0.12 solar masses. So, in less than half an hour, our 0.01 solar mass black hole has already absorbed more than 10% of the mass of this F class star, increasing its mass by a factor of more than 10, and that calculation didn't even take into account the fact that it will be pulling in matter faster as it gets bigger. Once it hits 0.1 solar masses, gravity at 25,000 km is now 2,160 g, and the freefall time at that range is down to 37 seconds.

    Obviously, this is just a rough order of magnitude estimate. But I think that the upper limit of the lifetime of a star harboring even a pretty small black hole is probably hours at best (and quite possibly much shorter). I don't think there's any way it could survive years with only occasional noticeable disruption.
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  10. #520
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    Grey: but you've not allowed for the outward radiation pressure. I'm sure there would be some and it would be significant. Black holes are the brightest objects in the universe. When you get this rate of matter spiralling in the energy output would be enormous. What's more the increase in temperature would also increase the fusion rate.
    I imagine the BH could orbit within a kind of bubble created by extreme outward radiation pressure.

  11. #521
    While looking up stuff on solar winds and the effects of it in the solar system, it might be able to allow dust to move along objects like asteroids or moons. The effect is small but nayba the solar wind of this star is putting a charge on some of the dust from say a comet and blocking more light then the comet alone. Now I sound like EU/PU atmers. I still think it is way to earlier to know for sure what is going on.
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    Quote Originally Posted by kzb View Post
    Grey: but you've not allowed for the outward radiation pressure. I'm sure there would be some and it would be significant. Black holes are the brightest objects in the universe. When you get this rate of matter spiralling in the energy output would be enormous. What's more the increase in temperature would also increase the fusion rate.
    I imagine the BH could orbit within a kind of bubble created by extreme outward radiation pressure.
    I don't think so. The Eddington Luminosity (the point at which the radiation pressure from an object balances the inward force of gravity and prevents it from accreting additional matter) for a 0.01 solar mass black hole would be about 320 solar luminosities. If the black hole is producing anywhere near this kind of energy, if would blow the star apart completely. Even if the black hole is producing just a few percent of this (which then wouldn't slow the accretion significantly), it would still be producing an order of magnitude more energy than the stellar core itself, and there's again no way that the whole thing could look like a stable F class star.
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  13. #523
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    Quote Originally Posted by kzb View Post

    There is a more prosaic and fairly boring explanation being proposed: this star is reaching the end of its main-sequence lifespan. Models of F-stars at this stage in their lives show they are very convective, and their output is thus unstable. It's as simple as that. We just happen to have caught this star during a very short intermediate stage, where it is beginning the process of leaving the main sequence.
    What surprises me is that this possibility doesn't seem to be given much weight. My intuition from the beginning is that it should be some intrinsic process (because otherwise it becomes contrived), but the original paper didn't take that idea seriously and I haven't really heard it before, though it seems plausible. Why is it that this explanation isn't given more weight?
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    Quote Originally Posted by Grey View Post
    I don't think so. The Eddington Luminosity (the point at which the radiation pressure from an object balances the inward force of gravity and prevents it from accreting additional matter) for a 0.01 solar mass black hole would be about 320 solar luminosities. If the black hole is producing anywhere near this kind of energy, if would blow the star apart completely. Even if the black hole is producing just a few percent of this (which then wouldn't slow the accretion significantly), it would still be producing an order of magnitude more energy than the stellar core itself, and there's again no way that the whole thing could look like a stable F class star.
    The end result seems to be the star blowing up, not so much being sucked in.

    There used to be a topic of discussion about what would happen if a small BH was dropped into the Earth. People used to say the planet would be cut in half as the BH fell through the planet and out the other side, and because the Earth revolves.

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    Quote Originally Posted by Jens View Post
    What surprises me is that this possibility doesn't seem to be given much weight. My intuition from the beginning is that it should be some intrinsic process (because otherwise it becomes contrived), but the original paper didn't take that idea seriously and I haven't really heard it before, though it seems plausible. Why is it that this explanation isn't given more weight?
    Apparently this is known as the Dirk Bonte Hypothesis. I've not been able to find it published though.

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    Quote Originally Posted by Jens View Post
    What surprises me is that this possibility doesn't seem to be given much weight. My intuition from the beginning is that it should be some intrinsic process (because otherwise it becomes contrived), but the original paper didn't take that idea seriously and I haven't really heard it before, though it seems plausible. Why is it that this explanation isn't given more weight?
    I think it's the sheer size and suddenness of the changes. I think there are numerous possible explanations for some small variation in a star's output, but the big sudden drop is something that we wouldn't expect to happen. That's pretty much the case with most of the explanations they looked at, which is why it's such a mysterious star, and why we're eager to have further observations (and hopefully, catch in the act again).
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    Quote Originally Posted by kzb View Post
    The end result seems to be the star blowing up, not so much being sucked in.
    I'm not saying that it will produce 320 solar luminosities. My point is that that's how much power it needs to produce to stop the flow of matter to it. Plenty of objects emit much less radiation than the Eddington limit; it's an upper bound. So, yes, black holes produce radiation pressure, and that can in principle prevent them from accreting more matter, or at least slow down the process. But even for a hypothetical substellar black hole, if it were producing even a few percent of the energy needed to affect its accretion rate in any significant way, that would be an order of magnitude or two above what we see coming from this star. So we know that a tiny black hole couldn't be producing that much radiation pressure (or even anywhere close to it), and hence should be accreting matter very fast.

    Quote Originally Posted by kzb View Post
    There used to be a topic of discussion about what would happen if a small BH was dropped into the Earth. People used to say the planet would be cut in half as the BH fell through the planet and out the other side, and because the Earth revolves.
    This would obviously have to be a much smaller black hole than we're even considering here. A black hole with the mass of the Moon would only have a radius of about 0.1 mm, but even that would totally distort the Earth if it passed through, just from the tidal effects. Usually, I've seen this question asking about a hypothetical black hole with the mass of a mountain (a few billion tons) or smaller. In that case, though, the event horizon is on the order of femtometers, the size of a proton. I think there are questions about how easy it would be for such a black hole to gain mass, with a size as small or smaller than the subatomic partciles themselves; we might need a quantum theory of gravity to really understand a black hole on that scale. Also, we think a black hole that small would emit significant Hawking radiation, so to gain mass, it has to accrete matter faster than it's emitting energy. For anything less than about 10 million tons, the expected Hawking radiation is actually higher than the Eddington luminosity, so it wouldn't gain mass at all without someone doing a lot of work to overcome that radiation pressure.

    But yes, I could imagine a tiny black hole punching little holes through the Earth with each pass (they'd fill in almost immediately, though, so it couldn't really cut the Earth in half).
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  18. #528
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    <<I'm not saying that it will produce 320 solar luminosities>>

    I don't know how to calculate the power, but I do know that BH-powered space drives have been proposed. They feature in a couple of Arthur C Clarke stories. When matter is accreted by a BH the power output is enormous, and exceeds fusion power mass for mass.

    The following link gives power output calculations for a supermassive BH, so I do not know how applicable it is to the current problem. 7% of the rest mass of infalling matter is converted to energy (factor of 10 higher than fusion). It seems to me that very significant power output could be achieved with a BH inside the body of a star.

    http://spacemath.gsfc.nasa.gov/news/6Page96.pdf
    Last edited by kzb; 2016-Aug-19 at 03:32 PM.

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    Quote Originally Posted by kzb View Post
    <<I'm not saying that it will produce 320 solar luminosities>>

    I don't know how to calculate the power, but I do know that BH-powered space drives have been proposed. They feature in a couple of Arthur C Clarke stories. When matter is accreted by a BH the power output is enormous, and exceeds fusion power mass for mass.

    The following link gives power output calculations for a supermassive BH, so I do not know how applicable it is to the current problem. 7% of the rest mass of infalling matter is converted to energy (factor of 10 higher than fusion). It seems to me that very significant power output could be achieved with a BH inside the body of a star.
    Oh, absolutely. I think in some cases the energy conversion can be even higher. My point, though, is that we know that the total power output from the star remains about the same as other similar stars (with occasional sudden drops in energy output). So even a pretty small black hole couldn't be producing enough radiation pressure to prevent it from accreting mass very quickly, because we'd see that radiation, and it would totally change the star. Conversely, in a situation where a small black hole inside a star does produce enough energy to stop it from accumulating mass, or even to slow it by any amount, the output from the black hole completely dwarfs the normal energy output of the star, with drastic consequences. Indeed, that's exactly what happens when a black hole forms inside a star normally: it produces far more power than the Eddington limit, and as a consequence blows all of the star's outer layers away in a supernova explosion, one of the largest releases of energy that there is.

    Running the numbers shows that there's no middle ground, though, for a black hole even as small as 0.01 solar masses. There's no point at which such a black hole inside a star can absorb a moderate amount of material, producing enough radiation pressure to keep it from gaining mass quickly, but having a small enough energy output that it doesn't completely overshadow the star.

    We could try running numbers with a much, much smaller black hole and see if it helps. For example, let's work backwards and find the size of a black hole with an Eddington Luminosity of 0.01 solar luminosities. A black hole that small could be producing just a small fraction of the output of an F class star, so it doesn't disrupt it too much, but it would still have enough outward radiation pressure to offset its gravity, and keep it from growing much. This ends up being a black hole with about 3 x 10-7 solar masses, or about 0.1 Earth masses. This is a black hole with a radius less than a millimeter, and the domain where its gravity is significant compared to the star is much smaller (using the same parameters as before, it's only about 100 km, instead of 25,000 km), so we're left trying to explain how something that small can cause a 22% drop in the observed output. Even if it bobbed up to the surface briefly, and completely blocked light in a 100 km area, it wouldn't be anywhere near enough; that would just be the effect of a small sunspot. And as you note, black holes are really bright objects, so if anything, we should probably see a brightening from the star in a case like this, rather than a darkening.

    I'll grant that it's theoretically possible that micro black holes, if they exist at all, could probably hang around in the cores of stars without changing too many things. They might even be able to achieve a kind of equilibrium where the radiation pressure keeps them from growing too fast, as long as their mass is less than most terrestrial planets. But I'm at a loss to see how a black hole small enough to do this without disrupting the star could account for the behavior seen in KIC 8462852: behaving essentially as a stable F class star, but with occasional sudden drops of luminosity of up to 22%.
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    Quote Originally Posted by Tom Mazanec View Post
    Wasn't there speculation at one time that a black hole in the sun would explain both ice ages and the old solar neutrino problem?
    The solar neutrino problem has been solved, and it didn't require the invocation of a black hole.

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    Quote Originally Posted by Amber Robot View Post
    The solar neutrino problem has been solved, and it didn't require the invocation of a black hole.
    That's true, but the point was that whoever proposed that solution must have thought that it was possible for a black hole to exist within the sun without devouring it. Do you have any insights into that?
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    Quote Originally Posted by Jens View Post
    That's true, but the point was that whoever proposed that solution must have thought that it was possible for a black hole to exist within the sun without devouring it. Do you have any insights into that?
    I don't know how mainstream this is, but there is a Wikipedia entry on quasi-stars. A protostar's core collapses into a black hole, but the surrounding layers of gas are massive enough to absorb the resulting energy. They burn like a star but are much bigger. They can only form in the very early universe. It is Wikipedia, and they also have an entry on Klingons. So... maybe not?

    Another funny one is the standard question about "what if an Earth massed black hole hit the sun?" Well, not much. It's pea sized and by the time it gets around to devouring the sun, the sun has already reached the end of it's life... approximately anyway. Usually this one get messed up when someone says "Earth sized" instead of "Earth mass". If it had an event horizon as big as the Earth, it is many times more massive than the sun already.
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    I wonder--if a galactic collision was big and messy enough--could that spawn some Quasi-Stars?

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    Quote Originally Posted by publiusr View Post
    I wonder--if a galactic collision was big and messy enough--could that spawn some Quasi-Stars?
    I suspect not, as a galaxy has a lot of empty space.
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    Quote Originally Posted by publiusr View Post
    I wonder--if a galactic collision was big and messy enough--could that spawn some Quasi-Stars?
    There would definitely be lots of star formation. All the molecular clouds in either galaxy would go crazy making new stars.
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    Quote Originally Posted by publiusr View Post
    I wonder--if a galactic collision was big and messy enough--could that spawn some Quasi-Stars?
    I don't think so. It seems they are millions of solar masses and need to accrete more every year to be sustained.

    This is the extreme end of putting a black hole in a star. You can do it mentally, but whether that happens in nature is hypothetical.
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    Quote Originally Posted by Jens View Post
    That's true, but the point was that whoever proposed that solution must have thought that it was possible for a black hole to exist within the sun without devouring it. Do you have any insights into that?
    Without knowing who actually proposed that, and the details of the suggestion, it's hard to know if it was a serious idea from someone who actually worked out the details in some way (and found that it seemed at least plausible) or an off-the-cuff idea from someone who didn't have anything to show to support the idea.
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    Quote Originally Posted by Solfe View Post
    I don't know how mainstream this is, but there is a Wikipedia entry on quasi-stars. A protostar's core collapses into a black hole, but the surrounding layers of gas are massive enough to absorb the resulting energy. They burn like a star but are much bigger. They can only form in the very early universe. It is Wikipedia, and they also have an entry on Klingons. So... maybe not?
    These seem to be a serious suggestion by actual astronomers, who've done the work to show that they are at least hypothetically possible. But they would also have to be thousands of solar masses, very short lived, and could only form in the early universe when metallicity was lower.* So they wouldn't be around today, and even if they were, such an object would look very different from a normal main sequence star. It's a fascinating idea, but very different from a micro black hole inside a more conventional star.



    * The very short explanation is that being made of heavier atoms and molecules allows a cloud of gas to cool more, which in turn results in smaller cloud fragments, which produces smaller stars.
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    A little bit more drama. The team released the first three months of data from the Kickstarter-funded observations, and apparently there were no events at all during that time. They have a year of funding, so this doesn't mean anything clear, but it's strange that there seemed to be some regularity (or at least some people claimed to see periodicity), but now there is nothing happening. I know it's really premature to say this, but it seems at least possible that it was a data problem with a cause that hasn't been determined. That would really be the most disappointing outcome imaginable, but like with the superluminal neutrino fiasco, when observations come out that are really weird, it's actually data problems that are the prime suspects.
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    Quote Originally Posted by Jens View Post
    A little bit more drama. The team released the first three months of data from the Kickstarter-funded observations, and apparently there were no events at all during that time. They have a year of funding, so this doesn't mean anything clear, but it's strange that there seemed to be some regularity (or at least some people claimed to see periodicity), but now there is nothing happening. I know it's really premature to say this, but it seems at least possible that it was a data problem with a cause that hasn't been determined. That would really be the most disappointing outcome imaginable, but like with the superluminal neutrino fiasco, when observations come out that are really weird, it's actually data problems that are the prime suspects.
    Now would that be a success of citizens direct funding science or not? I think "yes", but if so we are going to have to get used to a lot of disappointing things.
    Solfe

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