On the Physical Reality of Black Holes

Tim Thompson

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Tim Thompson
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A lot of people don't seem to like the idea of black holes. Understandable if you happen to run into one, but not if you simply wish to challenge the general validity of the idea. But whether you like the idea or not, it seems only reasonable that one should actually know what a black hole is before deciding, one way or the other. So I steal the following comment from the overcrowded "Lambda cosmology" thread to illustrate the point.
Zeuzzz said:
A black hole has zero volume and infinite density, creating what is known as a singularity.
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The "zero volume" and "infinite density" part applies only to the singularity itself, but the black hole is a considerably more complicated thing which enjoys a volume considerably larger than zero, and a density of finite value.

The word singularity is a term from mathematics and describes a point, or locus of points, where a given equation is undefined. The ratio 1/0, for instance, is not equal to infinity, but is rather undefined because you simply cannot do it, the arithmetic operation does not exist at all. However, the limit of the ratio 1/x as x approaches 0 is infinity. There is a distinct difference & important between the two ideas, which is left as an exercise for the reader to figure out. So we say that the equation 1/x = is singular if x=0.

The key is the singularity is a mathematical artifact and not a physical object. The singularity is not as such expected to exist, but rather to indicate that the singular equation needs to be replaced with one that is not singular, either from the same or a different theory, if one is to physically describe events at the singular points in spacetime (the points which are singular in one equation need not be singular in another; 1/x = y is singular if x=0, but x2=y is not singular for any non-infinite value of x).

Viewed from the outside, the singularity is hidden behind an event horizon so it cannot be seen. Once inside the event horizon, the geometry is such that all existing spacetime trajectories terminate at the singularity. What happens than is, of course, equally undefined.

So let us ask the question: Do black holes actually exist? How can we tell, by observation, one way or the other? The answer is to look for the event horizon. All compact astrophysical objects, except black holes, have a hard compact surface. Most of the objects that appear massive enough to be candidate black holes are accompanied by an accretion disk of infalling material which becomes extremely hot, and is easily visible to astronomers in X-rays. If the hot matter hits a hard surface, it will flare in a manner that indicates the presence of a hard surface. On the other hand, if the hot matter falls into a black hole it simply disappears with no appreciable fanfare. Hence, we should be able to observationally distinguish between the presence or absence of the unique event horizon of the black hole by its flaring behavior. We also know that any hard hot surface will emit thermal X-rays, whereas a black hole event horizon will have no detectable thermal emission. So we should be able to distinguish between a "normal" compact object (such as a neutron star or exotic quark star & etc.) and an event horizon by the presence or absence of a thermal component in X-rays.

These have been done and observations now positively indicates the presence of event horizons. See, for examples Paul, et al., 1998; Done & Gierliński, 2003; Narayan, 2003; McClintock, Narayan & Rybicki, 2004; Remillard, et al., 2006.

All of you who have your own alternative ideas in cosmology or relativity, and those of you who insist that black holes are just artifacts of some kind, and not physically real have a new problem. Observational evidence strongly supports the presence of event horizons, and only black holes are known to be associated with such things. So in order to argue that black holes are not physically real, you have to deal not only with the mathematics of general relativity (i.e., read Chandrasekhar's Mathematical Theory of Black Holes and prove he is wrong), but also with a small but growing mountain of observational evidence.

Black holes are physically real and they are not going away any time soon.
 
Tim Thompson said:
Observational evidence strongly supports the presence of event horizons, and only black holes are known to be associated with such things.
Click to expand...

Hi Tim,

I agree with your general approach, but I wish to note that these observations are not as cut-and-dried as you make them sound. It's absolutely true that these x-ray data are consistent with models of the x-ray emission from black hole accretion disks, and inconsistent with models of a neutron star accretion disk + surface. However, accretion disk modeling is extremely complex and messy, with multiple components (a disk with some vertical temperature, density, and opacity profile, some inner edge, some corona, some illumination of the outer disk by corona photons, etc.). If you're putting in a surface, then you get an additional surface, atmosphere, corona, etc., and more magnetic fields.

In short, if a crackpot came along and insisted that the papers you cite do not rule out his model, even though his model has thus-and-such surface and thus-and-such oddity ... well, it may be possible to argue with this particular crackpot model, but I wouldn't dare say that event horizons "have been observed" and call that the end of the argument. Just FYI.
 
The evidence that Sagittarius A* is a super massive black hole is pretty strong. Astronomers have imaged the full orbits of stars around it (from which they can infer its mass), and within a few years it should be possible to image the object itself down to scales smaller than its horizon.
 
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Tim Thompson said:
Zeuzzz said:
A black hole has zero volume and infinite density, creating what is known as a singularity.
Click to expand...
The "zero volume" and "infinite density" part applies only to the singularity itself, but the black hole is a considerably more complicated thing which enjoys a volume considerably larger than zero, and a density of finite value.
Click to expand...
In fact so considerably larger than zero, that it's effectively infinite. An idealized black hole (e.g., Schwarzschild) has a literally infinite spatial volume.

As a minor side issue, I don't see in what sense the singularity can be meaningfully ascribed any volume at all, even zero volume (a distinction analogous to the difference between having zero measure and having no measure in mathematics). This kind of curvature singularity is not something like a tip of a cone, which we can still treat as geometrical point even if the curvature is not defined there.
 
From a purely mathematical standpoint, I don't think there's anything distasteful about an event horizon, so I would think it's quite OK for things with event horizons to exist.

Singularities, however, are extremely unwelcome, and where they occur, I would say our mathematical modelling of physics has failed, so we need to improve the models.
 
Lennart Hyland said:
Just a little question, how long can a black hole exist? I wonder how long its lifetime is.
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The mass (and so lifetime) of a black hole is a balance between the incoming mass & radiation and their Hawking radiation. With the current cosmic background microwave this means that only black holes with a mass of less than that of the Moon can loss mass. All of the black holes that we have observed so far are stellar sized or greater.

So black holes exist until they are not replenished by the outside universe and begin to evaporate. When and if that happens depends on what happens to the universe - Future of an expanding universe.

A reasonable estimate is the that lifetime of a stellar sized black hole is ~1066 years and for a super-massive black hole ~10100 years.
 
Black Hole Comments

ben m said:
It's absolutely true that these x-ray data are consistent with models of the x-ray emission from black hole accretion disks, and inconsistent with models of a neutron star accretion disk + surface. ... but I wouldn't dare say that event horizons "have been observed" and call that the end of the argument.
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I think the constraint of being consistent with a model, as opposed to a "direct observation" is surely the case for the vast majority of astronomical observations, and so should simply be a 'given' for all cases. But I do want to add that, even though accretion disk modeling is complicated, and one should not overestimate the value of the observational evidence I have pointed to, neither should one underestimate the value of the evidence on the assumption that accretion disk modeling weakens the case any more than it really does. See, for instance, Done, Gierliński & Kubota, 2007 for an extensive review of accretion disk modeling. And see Narayan & McClintock, 2008, which directly addresses the interaction of the accretion disk with the event horizon.

In all cases I have linked to NASA/ADS webpages, which show citations to the papers, as well as references cited in the paper, so one can follow the literature in some detail as desired. "Alternative" thinkers & other critics tend to ignore astronomical observations, or concentrate on one paper that they can crib quotes from. I want to point out that there is an extensive literature on both models and observations that one must deal with the moment the idea comes up that black holes don't exist, or that the theory is in some way weak.

sol invictus said:
The evidence that Sagittarius A* is a super massive black hole is pretty strong. Astronomers have imaged the full orbits of stars around it (from which they can infer its mass), ...
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See the UCLA Galactic Center Group webpage has a very spiffy video reconstruction of the orbits, along with other images & data, and see Ghez, et al., 2008 for the detailed analysis of the stellar orbits.

sol invictus said:
... and within a few years it should be possible to image the object itself down to scales smaller than its horizon.
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Doelman, 2008 & Doelman, et al., 2008 present millimeter wavelength VLBI observations of the central black hole (Sag A*) which resolve structure only a few Schwarzschild radii larger than the expected size of Sag A*, so indeed it seems not that far off before we can image the event horizon of Sag A* directly. Shen, et al., 2005 already had set the size of the radio source at about 1 astronomical unit. And finally, see Falcke, Melia & Agol, 2000 who point out that an event horizon will cast a shadow (I think this is something peculiar to event horizons, but I don't know that), and that shadow may also soon be visible to VLBI observations.

Lennart Hyland said:
Just a little question, how long can a black hole exist? I wonder how long its lifetime is.
Click to expand...
Assuming that Hawking Radiation is a real phenomenon, then the lifetime (L) of a black hole, in seconds, works out to ...
L = M3/1.194x1016where M is the mass in kilograms. By this formula the lifetime of a solar mass black hole is about 2x1067 years, assuming that the black hole losses mass as Hawking radiation. Of course, real black holes are constantly accreting new mass, so the clock is not yet ticking on black holes.
 
A recent paper on the issue of whether black holes have event horizons.
Stellar disruption events support the existence of the black hole event horizon by Wenbin Lu, Pawan Kumar, Ramesh Narayan.
The authors looked at supermassive black holes and the light expected from stars colliding with a hypothetical surface. This would be like a stretched out supernova with light shining for months, perhaps even years.

Described at Starts With a Bang: Nothing escapes from a black hole, and now astronomers have proof
According to Wenbin Lu, a scientist who studied these observations to test the hard-surface theory,
Given the rate of stars falling onto black holes and the number density of black holes in the nearby universe, we calculated how many such transients Pan-STARRS should have detected over a period of operation of 3.5 years. It turns out it should have detected more than 10 of them, if the hard-surface theory is true.​
Given all the black holes with masses greater than 100 million solar masses, there should have been a definitive signature if there’s a hard surface outside of the black hole’s event horizon. Yet no signature at all was seen.
Click to expand...
 
There's also the gravitational wave evidence when two mutually orbiting black holes coalesce.
 
Tim Thompson said:
Assuming that Hawking Radiation is a real phenomenon, then the lifetime (L) of a black hole, in seconds, works out to ...
L = M3/1.194x1016where M is the mass in kilograms. By this formula the lifetime of a solar mass black hole is about 2x1067 years, assuming that the black hole losses mass as Hawking radiation. Of course, real black holes are constantly accreting new mass, so the clock is not yet ticking on black holes.
Click to expand...

In fact, they won't just accrete mass by sucking up matter either. As long as the CMB is higher temperature than the black hole, then they will gain more mass from sucking up photons than they will lose from Hawking radiation. A solar mass black hole has a temperature of around 1x10-7 Kelvin (heavier ones even lower), while the CMB is about 2.7 Kelvin, so the universe will have to expand and cool quite a bit before even a stellar mass black hole (let alone a supermassive one, which would be even colder) will start to lose any mass.

Then again, with a lifetime on the order of 2x1067 years, the time it takes the universe to cool might not be that significant to it.
 
Ben M already nailed it, but basically I would refrain from saying that an event horizon has been observed for any particular black hole. What we can say is that it's not a neutron star of that mass, that is to say, something where the surface is sufficiently outside the Schwarzschild radius for such an observation to be even possible.

We can also say that GR still works outside the Schwarzschild radius, which I suppose is a relief, but not unexpected. GR is kinda like the Energizer bunny. It just keeps working.

But things get a bit less clear cut when you get close to the Schwarzschild radius. I'm talking Planck length distance, and I'm not aware of any observations that would directly confirm what happens there. Not the least becaue of the insane redshift of any photons on the way out, and it all being drowned in the signal from the accretion disk.

E.g., I don't think there is any observation that directly confirms that all the matter is behind the event horizon, and it isn't, say, a gravastar.
 
There is black star which emit black light.

Center of every galaxys is supermassive concentrations which emit dark matter which have a nature of stars and of course nature of visible matter.

So, galaxys born inside to outside and it is something what we can proof with James Webb Telescope.

.
 
jonesdave116 said:
Sounds like LaViolette's nonsense.
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Well, expanding space is nonsense. Not even naked empire.

Expanding nucleus of atoms which recycling expanding pushing force which have also nature of expanding light which moving faster and faster same way what matter and light expanding is something what you can explain with words and visually way.

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@Pixie:
Wait, wait, did you just in all seriousness proposed that something emits dark? As in, taking seriously the old "Dark Sucker Theory" joke? :p
 
HansMustermann said:
@Pixie:
Wait, wait, did you just in all seriousness proposed that something emits dark? As in, taking seriously the old "Dark Sucker Theory" joke? :p
Click to expand...

Well, there is so density pushing force particles that our machine cant register this particles.

Well, this very density pushing force particles emit dark light and thats why our machine cant register this very density pushing force paticles / densers.

Dark matter with pulling force is joke.

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Pixie of key said:
There is black star which emit black light.

Center of every galaxys is supermassive concentrations which emit dark matter which have a nature of stars and of course nature of visible matter.

So, galaxys born inside to outside and it is something what we can proof with James Webb Telescope.

.
Click to expand...

There is Some evidence already.

Scientists detect radio echoes of a black hole feeding on a star

https://m.phys.org/news/2018-03-scientists-radio-echoes-black-hole.html

"We know that the radio waves are coming from really energetic electrons that are moving in a magnetic field—that is a well-established process," Pasham says. "The debate has been, where are these really energetic electrons coming from?"

Some scientists propose that, in the moments after the stellar explosion, a shockwave propagates outward and energizes the plasma particles in the surrounding medium, in a process that in turn emits radio waves. In such a scenario, the pattern of emitted radio waves would look radically different from the pattern of X-rays produced from infalling stellar debris.

"What we found basically challenges this paradigm," Pasham says."

😀
 
Pixie of key said:
Scientists detect radio echoes of a black hole feeding on a star

https://m.phys.org/news/2018-03-scientists-radio-echoes-black-hole.html

"We know that the radio waves are coming from really energetic electrons that are moving in a magnetic field—that is a well-established process," Pasham says. "The debate has been, where are these really energetic electrons coming from?"

Some scientists propose that, in the moments after the stellar explosion, a shockwave propagates outward and energizes the plasma particles in the surrounding medium, in a process that in turn emits radio waves. In such a scenario, the pattern of emitted radio waves would look radically different from the pattern of X-rays produced from infalling stellar debris.

"What we found basically challenges this paradigm," Pasham says."
Click to expand...
Scientists detect radio echoes of a black hole feeding on a star is a bit of evidence for actual supermassive black holes.

Note that the paradigm being challenged is not the existence of a supermassive black hole. It is the shockwave propagation after the stellar explosion. In that scenario I suspect the radio signals would be roughly spherically distributed while the x-ray signals would be a ray. Finding that the two distributions are similar suggests that it is the x-rays that cause the radio waves, not a shock wave.


N.B. This is not evidence for an fantasy of supermassive black holes emitting dark matter (see my post about the same article in the nearly 10 year old thread on this and other fantasies).
 
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No no no, he's not saying they emit dark matter. In fact, he's denying dark matter.

He's saying they emit actual dark. Without the matter part. Well, in his words "black light". As in, actual black photons.

Let's not do a strawman by trying to read a sane version of it ;)
 
HansMustermann said:
No no no, he's not saying they emit dark matter. In fact, he's denying dark matter.
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He has 2 stories:
"There is black star which emit black light."
"Center of every galaxys is supermassive concentrations which emit dark matter..."
"There is Some evidence already" links to a supermassive black hole science article thus the context is his second claim. I suspect that "black star" is his translation from Finnish of (stellar) black hole.

The part of "Dark matter with pulling force" he denies is actually the fact that gravity pulls. In his world, no force at all can pull and so both dark and normal matter push. Ditto for a child pulling a toy with a string. Ditto for two unlike charges attracting. etc.

There is no sane version of his clams and so we should not derail this thread.
 
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The universe is eternal.

The visible universe has a beginning which is based on eternal motion.

Motion is eternal.

Motion = energy.

Motion = pushing force.

Eternal circulation is based only on pushing force which is motion.

Therefore pulling force/arching space does not exist.

Thus the motion/energy of which the visible universe was born existed yet before the visible universe came into existence out of it.

In the eternal and infinite space there are extremely dense and massive objects that are very far away from each other. All of them are located far outside the visible universe and the expanding visible universe protrudes away from one such object. Thereby the expanding condensations absorb motion originally from other similar objects to themselves. This is the matter of motion/energy i.e. remains of very old detectable kind of universes.

These extremely dense and massive objects recycle the eternal motion/energy among each other and during this action there are detectable kinds of galaxies born out of the extremely dense motion/energy that is directed away from those very objects.

If there were no remains of the old universes that still have areas of different densities protruding in the contrary direction no detectable kind of visible universe could ever be born.

First the supermassive objects in the centers of galaxies are born out of zillions of individual condensations that expand and recycle the expanding motion/energy among each other.

The external motion/energy protruding towards gets the expansion of these objects to accelerate very strongly at the same time. As a result there is suddenly an extremely great pressure in the center of a large area with no gravitational force at all.

Now there is outward expanding motion/energy being pressed from the center of this area out of which new expanding stars come to existence by the aid of the external motion/energy in a similar manner. Also new detectable kind of matter is born consisting of the cores of expanding atoms that recycle among each other the expanding motion/energy with a nature of expanding light.

In this case the external motion originates from a supermassive object in another galaxy’s center that also expands in a manner that expanding motion/energy protrudes outward of it. This expanding motion/energy has the nature of expanding cores of atoms and thus it also has the nature of expanding stars.

http://www.onesimpleprinciple.com/

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Reality Check said:
He has 2 stories:
"There is black star which emit black light."
"Center of every galaxys is supermassive concentrations which emit dark matter..."
Click to expand...

The difference is that you read the supermassive concentrations as a black hole too (which is what I called the sane version), while I don't think he makes that connection.

That said, yeah, after his longer message I remember why I avoided his threads. I think my brain was trying to dig its way out through an ear when I was reading that.
 
HansMustermann said:
The difference is that you read the supermassive concentrations as a black hole too (which is what I called the sane version), while I don't think he makes that connection.
Click to expand...
He makes the connection here and in his other thread. He is watching the news from phys.org. Just about every time a supermassive black hole is mentioned up comes a "supermassive concentrations" post in that thread. He even connects cyclones on Jupiter to "galaxy center supermassive concentration"!
 
Reality Check said:
He makes the connection here and in his other thread. He is watching the news from phys.org. Just about every time a supermassive black hole is mentioned up comes a "supermassive concentrations" post in that thread. He even connects cyclones on Jupiter to "galaxy center supermassive concentration"!
Click to expand...

And there you go in his answer above. The "supermassive concentrations" in his "model" are pushing stuff away, not being attractors like our black holes. It's all over the place, really.
 
HansMustermann said:
And there you go in his answer above. The "supermassive concentrations" in his "model" are pushing stuff away, not being attractors like our black holes. It's all over the place, really.
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I agree. On the one hand he really wants to connect to real supermassive black holes in science but he is unable to release his denial of all pulling forces that make them physically possible. He has not thought about answering a basic question of how can they exist if all of the matter in them is being pushed apart by every force? N.B. he denies curvature of spacetime that prevents matter from escaping a black hole.
 
Reality Check said:
He makes the connection here and in his other thread. He is watching the news from phys.org. Just about every time a supermassive black hole is mentioned up comes a "supermassive concentrations" post in that thread. He even connects cyclones on Jupiter to "galaxy center supermassive concentration"!
Click to expand...

Yes, i make a connection with Jupiter red spot and galaxy center supermassive concentration because there is connection with this system.

Observations show that the stars are moving too fast on the outer circumference of the galaxies. they should protrude away from the center of the galaxy, according to their habits. really the stars are projecting out of the supermassive object of the galaxy center that pushes them away from the center of the galaxy.

This is not noticeable because the stars and all the substance expand in the same proportion. so there is a pushing force that maintains Jupiter's big red spot. it is pushed inside Jupiter all the time. It is from the Sun. and also the supermassive object of the galaxy center.

Jupiter is in the area between the Sun and the galaxy center. then those pushing forces will encounter a counterbalance and thus release a powerful push that pushes Jupiter strongly away from the center of the galaxy.

And it makes the center of Jupiter's center expand more intensively. therefore a faster expanding matter is pushed toward the surface of Jupiter. it maintains Jupiter's big red spot.

Not bad, you know 😀
 
"Iagree. On the one hand he really wants to connect to real supermassive black holes in science but he is unable to release his denial of all pulling forces that make them physically possible"

The birth of each supermassive item is like a small "big Bang" out of space in an already existing space. Extremely dense pushing / bursting force. Very small and dense recessions are needed that will recycle the pushing force. Then one supermassive object will emerge as they begin to expand one by two in an explosive manner. There is a very high pressure on the center of a new supermassive object. Without the pulling force.

And then supermassive concentration just expanding and emit expanding dark matter which have sometimes possibility expanding very fast when can born new expanding stars same way what supermassive concentrations born.

Forget stupid pulling force and stupid curving space.

.
 
This is the science forum, PoK. You've already said explicitly that you haven't got any science (or maths) backing up any of your absurd claims. Take your childish nonsense over to the humour section where it belongs.
 
MikeG said:
This is the science forum, PoK. You've already said explicitly that you haven't got any science (or maths) backing up any of your absurd claims. Take your childish nonsense over to the humour section where it belongs.
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Here is a scientific claim to you. an argument that can be scientifically examined.

if it exists physically, it takes space in space. it can be compressed with a dense pushing force. but not infinitely dense. it splits / expands less dense because of its own internal pressure. that is, pushing force. it is the driving force itself. its place from space can not be if it does not push it from the space of space. the question is.

What is the driving force? It can not be anything physically concrete in existence. as the substance is pushing force. you are a pushing force. as you move, you push the air out of the space where you are.

Your body's substance can not have the pulling force. no physically concrete existence can not have the pulling force. the force is not separate from the substance. the substance is power. it is a pushing force.

Lets try to tell something about pulling force with graviton.

I think you dont try, becsuse you know pulling force with particle is handwaving.

What about pulling force with curving space?

Lets tell something about curving space. Explain curving space with words or visually way. But hey, no any analogy. Something concrete, please.

If curving space is science, you should can explain with words how space curving.

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"What is the driving force? It can not be anything physically concrete in existence."

Should be

What is the PULLING or DRAWING force? It can not be anything physically concrete in existence.

By the way!!!

Quess why you dont have physics theory of everything?

Yes, because you believe, there is pulling force. You know, drawing force dont exist. No curving space.

No expanding space!!!

No stupid extra dimensions!!!

No dark matter with drawing or pulling force.

No dark energy which interactive with space somehow someway.

.
 
Well, I would, but yesterday's post where I tried to explain some physics at an over-simplified level got moved to abandon all hope. I'm sure it broke some rule or another, so I'd rather not anger the mods with more physics :p

You can still watch Leonard Susskind's lectures on youtube. E.g., the lectures on GR if you want words and drawings of how that curved space works. He's good, really.
 
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