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SpacyLuke
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The most massive black holes in the Universe

27 Dec 2018 01:48

I noticed there arent many of the black holes in the SE from this list:
https://en.wikipedia.org/wiki/List_of_m ... lack_holes

Also is it me or are all black holes in the SE very much alike?
They all look the same...
Would be nice to see something like this:
https://imgur.com/F1kRi9b
 
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The most massive black holes in the Universe

27 Dec 2018 16:20

SpacyLuke wrote:
Source of the post Also is it me or are all black holes in the SE very much alike?  They all look the same...Would be nice to see something like this:

While it might look nice, it's inaccurate.  Real black hole accretion disks do not look like that, specifically with respect to the color, brightness, and how those change with distance from the center.

SE's visualization of the black holes and their accretion disks is much more close to reality and uses most of the correct physics, including the gravitational lensing (using the Schwarschild metric), and the Doppler effect due to the disk's rotation.  The effective temperature of the disk (and hence its color and brightness) as a function of distance from the center is also modeled, although not perfectly.  In reality it should be even brighter and wider -- quite the opposite of what the artist's rendition showed! :)

To be more realistic, and add some variety, black hole accretion disks could be made volumetric, and their appearance based on GRMHD simulations of disks with different accretion rates.  Real black holes also spin (Kerr metric rather than Schwarzschild), which affects how close the inner part of the accretion disk gets to the event horizon.
 
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The most massive black holes in the Universe

27 Dec 2018 18:23

SE will probably look more like these than interstellar in the near future after EHT publishes the paper and data they are working on

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The most massive black holes in the Universe

27 Dec 2018 20:02

I have seen those preliminary models. Looks amazing!
 
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27 Dec 2018 21:04

DoctorOfSpace wrote:
Source of the post SE will probably look more like these than interstellar in the near future after EHT publishes the paper and data they are working on

One thing to be aware of with these models is that they do not represent what they look like in visible wavelengths, but rather in few millimeter wavelengths, or extremely high frequency radio/microwave range.  In these wavelengths the outer accretion disk (and the interstellar dust) become transparent, which make them optimal for the EHT observations to see the shape of the black hole's event horizon and what's going on very close to it.

They are definitely amazing and I'm very excited to see the real thing in real data. :)
 
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27 Dec 2018 21:24

As I said, more like, not identical. 

A volumetric accretion disk will be more cylindrical and widen the further out you go from the center into more of a toroidal shape.
Similar but not exact to this
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The most massive black holes in the Universe

27 Dec 2018 23:02

Watsisname wrote:
DoctorOfSpace wrote:
Source of the post SE will probably look more like these than interstellar in the near future after EHT publishes the paper and data they are working on

One thing to be aware of with these models is that they do not represent what they look like in visible wavelengths, but rather in few millimeter wavelengths, or extremely high frequency radio/microwave range.  In these wavelengths the outer accretion disk (and the interstellar dust) become transparent, which make them optimal for the EHT observations to see the shape of the black hole's event horizon and what's going on very close to it.

They are definitely amazing and I'm very excited to see the real thing in real data. :)

I really like that with certain black holes like Cygnus X-1 we can actually see the Cauchy horizon too! And go through it ;-)
 
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The most massive black holes in the Universe

27 Dec 2018 23:11

A-L-E-X wrote:
Source of the post I really like that with certain black holes like Cygnus X-1 we can actually see the Cauchy horizon too! And go through it

What are you talking about?
 
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The most massive black holes in the Universe

28 Dec 2018 00:24

Watsisname wrote:
A-L-E-X wrote:
Source of the post I really like that with certain black holes like Cygnus X-1 we can actually see the Cauchy horizon too! And go through it

What are you talking about?

I took a trek to the Cygnus X-1 black hole and it actually let me go through it and emerge on the other side (somewhere else in space).  There were two event horizons, the initial one (event horizon) and a second horizon (which I assume was the Cauchy horizon) and then I popped back out into space.
 
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28 Dec 2018 00:37

Oh, haha.

Black holes in SE don't actually have an inner or Cauchy horizon (and neither do black holes in nature).  Despite appearances you cannot fly inside their event horizons, either.
 
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28 Dec 2018 00:48

Watsisname wrote:
Oh, haha.  

Black holes in SE don't actually have an inner or Cauchy horizon (and neither do black holes in nature).  Despite appearances you cannot fly inside their event horizons, either.

Was that a bug in the program then perhaps? I just aimed it through the thing and there was a period of blackness and then I saw another hole on the other side with a weird green light and emerged back into space lol.
About Cauchy Horizons existing in nature what do you think of this Wat
https://en.wikipedia.org/wiki/Cauchy_horizon
http://adsabs.harvard.edu/abs/1982RSPSA.384..301C
https://en.wikipedia.org/wiki/Reissner% ... black_hole

from this research

https://www.quantamagazine.org/mathemat ... -20180517/

But as you continue to travel into the black hole, eventually you pass another horizon, known as the Cauchy horizon. Here things get screwy. Einstein’s equations start to report that many different configurations of space-time could unfold. They’re all different, yet they all satisfy the equations. The theory cannot tell us which option is true. For a physical theory, it’s a cardinal sin.

“The loss of predictability that we seem to find in general relativity was very disturbing,” said Eric Poisson, a physicist at the University of Guelph in Canada.

Roger Penrose proposed the strong cosmic censorship conjecture to restore predictability to Einstein’s equations. The conjecture says that the Cauchy horizon is a figment of mathematical thought. It might exist in an idealized scenario where the universe contains nothing but a single rotating black hole, but it can’t exist in any real sense.

The reason, Penrose argued, is that the Cauchy horizon is unstable. He said that any passing gravitational waves should collapse the Cauchy horizon into a singularity — a region of infinite density that rips space-time apart. Because the actual universe is rippled with these waves, a Cauchy horizon should never occur in the wild.

As a result, it’s nonsensical to ask what happens to space-time beyond the Cauchy horizon because space-time, as it’s regarded within the theory of general relativity, no longer exists. “This gives one a way out of this philosophical conundrum,” said Dafermos.

This new work shows, however, that the boundary of space-time established at the Cauchy horizon is less singular than Penrose had imagined.

To Save a Black Hole
Dafermos and Luk, a mathematician at Stanford University, proved that the situation at the Cauchy horizon is not quite so simple. Their work is subtle — a refutation of Penrose’s original statement of the strong cosmic censorship conjecture, but not a complete denial of its spirit.

Building on methods established a decade ago by Christodoulou, who was Dafermos’s adviser in graduate school, the pair showed that the Cauchy horizon can indeed form a singularity, but not the kind Penrose anticipated. The singularity in Dafermos and Luk’s work is milder than Penrose’s — they find a weak “light-like” singularity where he had expected a strong “space-like” singularity. This weaker form of singularity exerts a pull on the fabric of space-time but doesn’t sunder it. “Our theorem implies that observers crossing the Cauchy horizon are not torn apart by tidal forces. They may feel a pinch, but they are not torn apart,” said Dafermos in an email.

Because the singularity that forms at the Cauchy horizon is in fact milder than predicted by the strong cosmic censorship conjecture, the theory of general relativity is not immediately excused from considering what happens inside. “It still makes sense to define the Cauchy horizon because one can, if one wishes, continuously extend the space-time beyond it,” said Harvey Reall, a physicist at the University of Cambridge.

Dafermos and Luk prove that space-time extends beyond the Cauchy horizon. They also prove that from the same starting point, it can extend in any number of ways: Past the horizon “there are many such extensions that one could entertain, and there is no good reason to prefer one to the other,” said Dafermos.

Yet — and here’s the subtlety in their work — these nonunique extensions of space-time don’t mean that Einstein’s equations go haywire beyond the horizon.
 
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28 Dec 2018 00:53

Yes, just a glitch.  And no, you never passed inside the event horizon.  Even when the blackness seems to envelop you and the sky compressed to a small disk, you are still outside the horizon.  This is because the camera renders the view as if you are stationary at that point, which means enormous upward acceleration to stay in place against the gravity, which causes relativistic distortion to your view.

A-L-E-X wrote:
Source of the post About Cauchy Horizons existing in nature what do you think of this Wat

Those are features of the mathematical vacuum solutions to rotating or charged black holes, which assume that the only matter present is already at the central singularity.  Real black holes do not have these features.  They are rather a symptom of these solutions no longer accurately representing reality.  A clue is that these solutions predict that matter piles up near the inner horizon, which then contradicts the initial assumption that it all lies at the singularity.

An analogy is to imagine a waterfall that falls down a cliff and then smoothly flows back up the other side of the valley.  You could argue such a waterfall obeys principles of physics like energy conservation.  But it never happens in nature.  What actually happens is the flow breaks down into turbulence at the bottom.  A similar thing happens to the space-time inside of black holes.
 
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The most massive black holes in the Universe

28 Dec 2018 01:16

Watsisname wrote:
Yes, just a glitch.  And no, you never passed inside the event horizon.  Even when the blackness seems to envelop you and the sky compressed to a small disk, you are still outside the horizon.  This is because the camera renders the view as if you are stationary at that point, which means enormous upward acceleration to stay in place against the gravity, which causes relativistic distortion to your view.

A-L-E-X wrote:
Source of the post About Cauchy Horizons existing in nature what do you think of this Wat

Those are features of the mathematical vacuum solutions to rotating or charged black holes, which assume that the only matter present is already at the central singularity.  Real black holes do not have these features.  They are rather a symptom of these solutions no longer accurately representing reality.  A clue is that these solutions predict that matter piles up near the inner horizon, which then contradicts the initial assumption that it all lies at the singularity.

An analogy is to imagine a waterfall that falls down a cliff and then smoothly flows back up the other side of the valley.  You could argue such a waterfall obeys principles of physics like energy conservation.  But it never happens in nature.  What actually happens is the flow breaks down into turbulence at the bottom.  A similar thing happens to the space-time inside of black holes.

Thanks Wat, did you have a chance to read the article that I posted in the edit?  What do you think of it?  They actually think that space-time can behave normally beyond the Cauchy horizon.
I wonder if ER=EPR is related to this.
https://www.quantamagazine.org/wormhole ... -20150424/

Then in 2012 Polchinski, along with Ahmed Almheiri, Donald Marolf and James Sully, all of them at the time at Santa Barbara, came up with an insight so startling it basically said to physicists: Hold everything. We know nothing.

The so-called AMPS paper (after its authors’ initials) presented a doozy of an entanglement paradox — one so stark it implied that black holes might not, in effect, even have insides, for a “firewall” just inside the horizon would fry anyone or anything attempting to find out its secrets.

Scaling the Firewall       
Here’s the heart of their argument: If a black hole’s event horizon is a smooth, seemingly ordinary place, as relativity predicts (the authors call this the “no drama” condition), the particles coming out of the black hole must be entangled with particles falling into the black hole. Yet for information not to be lost, the particles coming out of the black hole must also be entangled with particles that left long ago and are now scattered about in a fog of Hawking radiation. That’s one too many kinds of entanglements, the AMPS authors realized. One of them would have to go.

The reason is that maximum entanglements have to be monogamous, existing between just two particles. Two maximum entanglements at once — quantum polygamy — simply cannot happen, which suggests that the smooth, continuous space-time inside the throats of black holes can’t exist. A break in the entanglement at the horizon would imply a discontinuity in space, a pileup of energy: the “firewall.”


David Kaplan explores one of the biggest mysteries in physics: the apparent contradiction between general relativity and quantum mechanics.
Video: David Kaplan explores one of the biggest mysteries in physics: the apparent contradiction between general relativity and quantum mechanics.

Filming by Petr Stepanek. Editing and motion graphics by MK12. Music by Steven Gutheinz.
The AMPS paper became a “real trigger,” said Stephen Shenker, a physicist at Stanford, and “cast in sharp relief” just how much was not understood. Of course, physicists love such paradoxes, because they’re fertile ground for discovery.

Both Susskind and Maldacena got on it immediately. They’d been thinking about entanglement and wormholes, and both were inspired by the work of Mark Van Raamsdonk, a physicist at the University of British Columbia in Vancouver, who had conducted a pivotal thought experiment suggesting that entanglement and space-time are intimately related.

“Then one day,” said Susskind, “Juan sent me a very cryptic message that contained the equation ER = EPR. I instantly saw what he was getting at, and from there we went back and forth expanding the idea.”

Their investigations, which they presented in a 2013 paper, “Cool Horizons for Entangled Black Holes,” argued for a kind of entanglement they said the AMPS authors had overlooked — the one that “hooks space together,” according to Susskind. AMPS assumed that the parts of space inside and outside of the event horizon were independent. But Susskind and Maldacena suggest that, in fact, particles on either side of the border could be connected by a wormhole. The ER = EPR entanglement could “kind of get around the apparent paradox,” said Van Raamsdonk. The paper contained a graphic that some refer to half-jokingly as the “octopus picture” — with multiple wormholes leading from the inside of a black hole to Hawking radiation on the outside.


The ER = EPR idea posits that entangled particles inside and outside of a black hole’s event horizon are connected via wormholes.

Olena Shmahalo/Quanta Magazine
In other words, there was no need for an entanglement that would create a kink in the smooth surface of the black hole’s throat. The particles still inside the hole would be directly connected to particles that left long ago. No need to pass through the horizon, no need to pass Go. The particles on the inside and the far-out ones could be considered one and the same, Maldacena explained — like me, myself and I. The complex “octopus” wormhole would link the interior of the black hole directly to particles in the long-departed cloud of Hawking radiation.

Holes in the Wormhole
No one is sure yet whether ER = EPR will solve the firewall problem. John Preskill, a physicist at the California Institute of Technology in Pasadena, reminded readers of Quantum Frontiers, the blog for Caltech’s Institute for Quantum Information and Matter, that sometimes physicists rely on their “sense of smell” to sniff out which theories have promise. “At first whiff,” he wrote, “ER = EPR may smell fresh and sweet, but it will have to ripen on the shelf for a while.”

Whatever happens, the correspondence between entangled quantum particles and the geometry of smoothly warped space-time is a “big new insight,” said Shenker. It’s allowed him and his collaborator Douglas Stanford, a researcher at the Institute for Advanced Study, to tackle complex problems in quantum chaos through what Shenker calls “simple geometry that even I can understand.”

To be sure, ER = EPR does not yet apply to just any kind of space, or any kind of entanglement. It takes a special type of entanglement and a special type of wormhole. “Lenny and Juan are completely aware of this,” said Marolf, who recently co-authored a paper describing wormholes with more than two ends. ER = EPR works in very specific situations, he said, but AMPS argues that the firewall presents a much broader challenge.

Like Polchinski and others, Marolf worries that ER = EPR modifies standard quantum mechanics. “A lot of people are really interested in the ER = EPR conjecture,” said Marolf. “But there’s a sense that no one but Lenny and Juan really understand what it is.” Still, “it’s an interesting time to be in the field.”

http://quantumfrontiers.com/2013/06/07/ ... wormholes/
 
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28 Dec 2018 02:59

A-L-E-X wrote:
Source of the post Thanks Wat, did you have a chance to read the article that I posted in the edit?  What do you think of it?  They actually think that space-time can behave normally beyond the Cauchy horizon.

I've read portions of their paper.  The space-time beyond the Cauchy horizon in their analysis is definitely not well behaved.  It is continuous, but it is not smooth (differentiable), and can not be extended in a way which is satisfied by the equations of general relativity.  General relativity requires the space-time be differentiable.  

So what they showed is that even though Penrose's argument for why a Cauchy horizon would be prevented in nature is wrong, this Kerr vacuum solution (specifically in terms of the deep interior) still does not reflect nature.  The metric leads to predictions that again contradict its own formulation.  What actually happens deep inside of real black holes has to be different, and probably not described by a Cauchy horizon where physics becomes indeterminable.  In a way they are verifying Penrose's objection to Cauchy horizons -- just for a more subtle reason.

I should probably also explain what a Cauchy horizon is for everyone, since it's a rather confusing term.  It is not the same thing as the event horizon (that one-way boundary where things can go in but never come out).  It has more to do with extendability from some starting point.  If you start with some initial conditions to the space-time outside the black hole, and then trace the space-time inward (imagine for example a set of astronauts who map out the space-time as they plummet into the black hole, or a set of light rays), then the Cauchy horizon is the boundary within which there is no unique extension to that space-time.

More clues to the failure of the Kerr solution within this region lie scattered through the paper as well.  An example is the infinite blueshift of signals reaching an observer near the inner/Cauchy horizon.  Other studies have shown this as well, and sometimes call it a "mass inflation singularity".  Kip Thorne talks about them in some of his popular books.  They arise basically because the Kerr metric makes the central singularity gravitationally repulsive (you can think of it as centrifugal force), which makes matter pile up near the inner horizon.  But then time dilation causes everything that falls into the black hole in the future to meet up with that as well, forming an infinitely blueshifted singularity rushing inwards.  This mass inflation singularity rapidly leads to conditions that break down the Kerr solution.

 
Long story short, the space-time gets extremely chaotic here, and that is what I refer to by analogy to turbulence with the waterfall example.  It is why relativists who study black holes think the Kerr vacuum solution does not describe the interior of real black holes.

A-L-E-X wrote:
Source of the post I wonder if ER=EPR is related to this.

They are fairly unrelated.  ER=EPR has more to do with entanglement, and what would happen if you had two clouds of particles that were entangled with one another, and collapsed each into a black hole without destroying that entanglement.  The conjecture predicts the two black holes would be joined inside by a wormhole.  (This does not mean that falling into one of those black holes would spit you out of the other one.  It's still certain death if you tried.  Rather, it means two observers who made two such black holes, and falling into them at an appropriate time, would end up meeting each other inside.)

This prediction also isn't the motivation or even the main thrust of ER=EPR, but a curious and fun consequence of it.  The motivation was to explore a possible union between principles of quantum mechanics, information theory, and space-time geometry, with the idea being that they might have a lot to do with one another.  But much of it goes way beyond my pay-grade. :)
 
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The most massive black holes in the Universe

28 Dec 2018 04:40

Watsisname wrote:
A-L-E-X wrote:
Source of the post Thanks Wat, did you have a chance to read the article that I posted in the edit?  What do you think of it?  They actually think that space-time can behave normally beyond the Cauchy horizon.

I've read portions of their paper.  The space-time beyond the Cauchy horizon in their analysis is definitely not well behaved.  It is continuous, but it is not smooth (differentiable), and can not be extended in a way which is satisfied by the equations of general relativity.  General relativity requires the space-time be differentiable.  

So what they showed is that even though Penrose's argument for why a Cauchy horizon would be prevented in nature is wrong, this Kerr vacuum solution (specifically in terms of the deep interior) still does not reflect nature.  The metric leads to predictions that again contradict its own formulation.  What actually happens deep inside of real black holes has to be different, and probably not described by a Cauchy horizon where physics becomes indeterminable.  In a way they are verifying Penrose's objection to Cauchy horizons -- just for a more subtle reason.

I should probably also explain what a Cauchy horizon is for everyone, since it's a rather confusing term.  It is not the same thing as the event horizon (that one-way boundary where things can go in but never come out).  It has more to do with extendability from some starting point.  If you start with some initial conditions to the space-time outside the black hole, and then trace the space-time inward (imagine for example a set of astronauts who map out the space-time as they plummet into the black hole, or a set of light rays), then the Cauchy horizon is the boundary within which there is no unique extension to that space-time.

More clues to the failure of the Kerr solution within this region lie scattered through the paper as well.  An example is the infinite blueshift of signals reaching an observer near the inner/Cauchy horizon.  Other studies have shown this as well, and sometimes call it a "mass inflation singularity".  Kip Thorne talks about them in some of his popular books.  They arise basically because the Kerr metric makes the central singularity gravitationally repulsive (you can think of it as centrifugal force), which makes matter pile up near the inner horizon.  But then time dilation causes everything that falls into the black hole in the future to meet up with that as well, forming an infinitely blueshifted singularity rushing inwards.  This mass inflation singularity rapidly leads to conditions that break down the Kerr solution.

 
Long story short, the space-time gets extremely chaotic here, and that is what I refer to by analogy to turbulence with the waterfall example.  It is why relativists who study black holes think the Kerr vacuum solution does not describe the interior of real black holes.

A-L-E-X wrote:
Source of the post I wonder if ER=EPR is related to this.

They are fairly unrelated.  ER=EPR has more to do with entanglement, and what would happen if you had two clouds of particles that were entangled with one another, and collapsed each into a black hole without destroying that entanglement.  The conjecture predicts the two black holes would be joined inside by a wormhole.  (This does not mean that falling into one of those black holes would spit you out of the other one.  It's still certain death if you tried.  Rather, it means two observers who made two such black holes, and falling into them at an appropriate time, would end up meeting each other inside.)

This prediction also isn't the motivation or even the main thrust of ER=EPR, but a curious and fun consequence of it.  The motivation was to explore a possible union between principles of quantum mechanics, information theory, and space-time geometry, with the idea being that they might have a lot to do with one another.  But much of it goes way beyond my pay-grade. :)

But I (and I'm sure many others) like your explanation MUCH better Wat!  Intuitively, I had always thought that black holes were macro versions of quantum objects, which is why they seem to be singularities.  There seems to be a natural connection between wormhole tunneling and quantum tunneling (although the authors made it clear this does not mean the worm holes are traversable.)
About relating the centrifugal force to rotating black holes, would that be a reason why the singularity might be a ring rather than a point?  In the centrifugal force (for example, let's take hurricanes- so in this case- the Coriolis force), there is a region of calm in the middle (the "eye"); could such a thing exist inside a black hole- the equivalent would be a region of 0 g at the very center, surrounded by an area of near infinite g which would comprise the "eye wall."  A reverse form of gravity interests me for some other reasons (for example, is it possible using the paragraph below, for such a solution to create an inflationary and expanding universe like ours?)  And what about the interior structure of two colliding supermassive black holes (this must be a rare event, but possible since galaxies do merge.  I shudder to think what the interior of M87's black hole- that cosmic cannibal- must be like!)

Even without the Cauchy horizon, is a new space-time (that is, new universe) still possible once beyond the event horizon?  Our own universe could be described that way (I remember you said you found that possibility intriguing.)  Perhaps this infinite pile up of matter plus the intense gravitation is what would make it possible?

The interconnections between the three things you mentioned is very intriguing, it's basically the beginnings of a road map to describe black holes (and our universe- and perhaps others) as cosmic quantum computers!

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