Black Hole: Why do we believe that matter could be such dense?

[Strange]

30 minutes ago, michel123456 said:

If that is true, then for the external observer the BH is void, all its mass lies on its surface at the EH.

You need to take Q-reeus's comments with a pint of salt. He thinks GR is wrong and cherry-picks papers and articles that seem to agree with him.

This, in particular, is not true. For one thing, there is no surface and so nothing to stop material falling in. And for another, the event horizon grows to encompass matter falling in so it wouldn't even appear to be "frozen" at the surface.

You liked the statement that there can only be one reality and so, because from the point of view of matter falling into the black hole there is nothing to stop it, you can't have an alternative reality where it stops.

[beecee]

5 hours ago, Tim88 said:

Anyway, it makes much logical sense, even in relativity there can only be one single reality!

 

3 hours ago, michel123456 said:

If that is true, then for the external observer the BH is void, all its mass lies on its surface at the EH.

Yet there can be any number of different frame of references, and each frame is as valid and as real as the other.

 

 

2 hours ago, Strange said:

You need to take Q-reeus's comments with a pint of salt. He thinks GR is wrong and cherry-picks papers and articles that seem to agree with him.

This, in particular, is not true. For one thing, there is no surface and so nothing to stop material falling in. And for another, the event horizon grows to encompass matter falling in so it wouldn't even appear to be "frozen" at the surface.

You liked the statement that there can only be one reality and so, because from the point of view of matter falling into the black hole there is nothing to stop it, you can't have an alternative reality where it stops.

Correct. I mentioned recently the "Dying Pulse Train" effect. This as far as I know eliminates any possibility of any surface at or below the EH.

http://www.indiana.edu/~geol105/images/gaia_chapter_1/death_spiral.htm

"NASA's Hubble Space Telescope may have, for the first time, provided direct evidence for the existence of black holes by observing the disappearance of matter as it falls beyond the "event horizon."

[michel123456]

11 hours ago, beecee said:

Correct. I mentioned recently the "Dying Pulse Train" effect. This as far as I know eliminates any possibility of any surface at or below the EH.

http://www.indiana.edu/~geol105/images/gaia_chapter_1/death_spiral.htm

"NASA's Hubble Space Telescope may have, for the first time, provided direct evidence for the existence of black holes by observing the disappearance of matter as it falls beyond the "event horizon."

Nice. In this case doesnt'it mean that the accretion disk is a spiral? And that the observer close to the EH , looking outside, will observe the Universe as if it was spiraling around him, in a similar way as we are actually looking at the Milky Way?

[MigL]

Here is a simple thought experiment...

You are in a safe orbit around a Black Hole, well outside the event horizon.
You tie a rope to an object, and hurl that object towards the Black Hole.
You see the light ( signal ) from the object becoming fainter and fainter as it approaches the EH, and its wavelength stretches to infinity as it reaches the EH so that the signal you are receiving from it is effectively temporally frozen.
Do you think the rope that is attached to the object will go slack, since the object has apparently stopped moving ?
Or do you think it will still be pulled in after the object has 'frozen' ?

[Tim88]

On 4/18/2019 at 7:05 PM, michel123456 said:

"even in relativity there can only be one single reality" - Happy to read that from someone like you.

"From someone like me"? It's a corner stone of doing science....

On 4/18/2019 at 7:05 PM, michel123456 said:

["The in-faller 'really stops cold' at EH as directly measured by string motion at external observer"] If that is true, then for the external observer the BH is void, all its mass lies on its surface at the EH.

Just now I got an email from Qreeus telling me that he found a mistake in that analysis. Indeed, that could hardly have been correct, as it seems obvious that in that region anything has to keep moving at locally c.

On 4/18/2019 at 7:39 PM, Strange said:

[..] For one thing, there is no surface and so nothing to stop material falling in. And for another, the event horizon grows to encompass matter falling in so it wouldn't even appear to be "frozen" at the surface.

There is indeed no literal surface; instead, as interpreted by a distant observer, there is the huge gravitational potential that slows down in-falling objects so much that their radial speed becomes nearly zero.

Further, a growing event horizon will of course displace that "surface" to beyond that position - kind of "burying" the particle inside the zone of extremely high gravitational potential. If I'm not mistaken, the gravitational potential won't be reduced below that "surface"; consequently, such burying cannot make it speed up again.

Edited April 21, 2019 by Tim88

[Strange]

31 minutes ago, Tim88 said:

Further, a growing event horizon will of course displace that "surface" to beyond that position - kind of "burying" the particle inside the zone of extremely high gravitational potential. If I'm not mistaken, the gravitational potential won't be reduced below that "surface"; consequently, such burying cannot make it speed up again.

It never slowed down, so it will continue to increase in speed after it passes the event horizon.

Form the external observers frame of reference, it ceases to be visible before it reaches the event horizon so the "frozen" thing is moot anyway.

[beecee]

1 hour ago, Tim88 said:

"From someone like me"? It's a corner stone of doing science....

As I mentioned before to another, all frames of references are as real and as valid as each other....That is another corner stone.

1 hour ago, Tim88 said:

Just now I got an email from Qreeus telling me that he found a mistake in that analysis. Indeed, that could hardly have been correct, as it seems obvious that in that region anything has to keep moving at locally c.

There is indeed no literal surface; instead, as interpreted by a distant observer, there is the huge gravitational potential that slows down in-falling objects so much that their radial speed becomes nearly zero.

Further, a growing event horizon will of course displace that "surface" to beyond that position - kind of "burying" the particle inside the zone of extremely high gravitational potential. If I'm not mistaken, the gravitational potential won't be reduced below that "surface"; consequently, such burying cannot make it speed up again.

 Two recent experiments have shown GR flavoured BH's to be now near certain and accepted by most reputable scientists. Even many years ago, the evidence was strong........

 I mentioned recently the "Dying Pulse Train" effect. This as far as I know eliminates any possibility of any surface at or below the EH.

http://www.indiana.edu/~geol105/images/gaia_chapter_1/death_spiral.htm

 

And of course as also mentioned earlier, and confirmed by Strange just above, we never actually see anything freeze at or near the EH, rather just gradually red shifted until beyond the viewing range of our equipment.

Edited April 21, 2019 by beecee

[Tim88]

35 minutes ago, Strange said:

It never slowed down, so it will continue to increase in speed after it passes the event horizon.

Form the external observers frame of reference, it ceases to be visible before it reaches the event horizon so the "frozen" thing is moot anyway.

"It never slowed down"??. Correct is to say that -of course- from its own frame of measurements, it never slows down.

From our frame of reference not only those objects become invisible, anything that would be observed by co-moving observers is unverifiable - moot as you say.

 

[beecee]

2 minutes ago, Tim88 said:

From our frame of reference not only those objects become invisible, anything that would be observed by co-moving observers is unverifiable - moot as you say.

The various effects of gravitational time dilation with regards to objects/matter/energy approaching an EH, in any frame of reference do nothing to invalidate the overwhelming evidence to support the "Gravitationally Completely Collapsed Object" as defined by GR, or if you like the BH. The evidence supporting them is verifiable. 

[Tim88]

41 minutes ago, beecee said:

The various effects of gravitational time dilation with regards to objects/matter/energy approaching an EH, in any frame of reference do nothing to invalidate the overwhelming evidence to support the "Gravitationally Completely Collapsed Object" as defined by GR, or if you like the BH. The evidence supporting them is verifiable. 

That's more to the point. Do you mean that simulations that have particles forever more slowly falling towards the centre, using GR equations from our point of view, do not agree with observations?

On second thought, likely you just mean that there is overwhelming support for the gravitational collapse of stars, which is getting back to the topic of this thread.

Edited April 21, 2019 by Tim88
rephrase and second thought

[beecee]

32 minutes ago, Tim88 said:

That's more to the point. Do you mean that simulations that have objects forever more slowly falling towards the black hole, using GR equations from our point of view, do not agree with observations? Or even, that such GR simulations have been "overwhelmingly" disproved? If so, links to articles that show that overwhelming evidence would be very useful in this thread.

My point again is that all observers in as many frames of references as you wish, can all take their frame as valid. Your frame far away watching me get red shifted and fade from view as I approach the EH is real and valid. In my own frame as I cross the EH at a speed approaching "c'" that is just as valid to me. I don't know what you mean with regards to simulations, or any supposed "disproved" GR, but it is wrong and from what I have seen on comments by our former anti GR speculator, based on ignorance.

With regards to links, I am at the end of a busy day and about to retire so I suggest you peruse the many many reputable links and scientific papers, some here, others in the other BH and HR threads, that show conclusively that GR and BH's are now overwhelmingly evidenced and generally supported in mainstream science. That fact will never be invalidated by and Tom, Dick or Harry on any science forum, open to the general public.

 

 

 

Edited April 21, 2019 by beecee

[Airbrush]

Would it be correct to say that between the central singularity and the event horizon is a perfect vacuum?  How could any particles exist inside the event horizon and not be instantly absorbed by the singularity?  As particles enter the event horizon are they attracted towards the center at light speed?  So how could the interior of a black hole, outside the central region, NOT be a perfect vacuum?

Edited April 22, 2019 by Airbrush

[Strange]

4 minutes ago, Airbrush said:

Would it be correct to say that between the central singularity and the event horizon is a perfect vacuum?  How could any particles exist inside the event horizon and not be instantly absorbed by the singularity?  As particles enter the event horizon are they attracted towards the center at light speed?  So how could the interior of a black hole, outside the central region, NOT be a perfect vacuum?

If large amounts of matter are falling into the black hole then, as far as we know, the interior will be full of that matter falling inwards. It will take a finite time for that matter to reach the centre, meanwhile more matter is continuously arriving. A waterfall is still full of water, even though it is free falling towards the ground.

Talking of waterfalls: A Black Hole is a Waterfall of Space

[MigL]

While we can say that it should be 'full' of infalling stuff, Strange, the reality is that an observer who has crossed the EH will never see or detect anything 'ahead' of himself. Any and all information is forbidden from travelling radially 'outward' from the central singularity, as there are no available paths, and that 'direction' leads to the past. All he 'sees' ahead of himself is darkness.

The EH causally disconnects the interior from the exterior AND any event preceding an infalling ( past the EH ) observer, as that event is now in the future.

[Strange]

38 minutes ago, MigL said:

While we can say that it should be 'full' of infalling stuff, Strange, the reality is that an observer who has crossed the EH will never see or detect anything 'ahead' of himself. Any and all information is forbidden from travelling radially 'outward' from the central singularity, as there are no available paths, and that 'direction' leads to the past. All he 'sees' ahead of himself is darkness.

The EH causally disconnects the interior from the exterior AND any event preceding an infalling ( past the EH ) observer, as that event is now in the future.

I have been told that you would be able to see matter that fell in ahead of you because you would "catch up" with the photons emitted by it. But I am not going to argue the point!

[Airbrush]

On 4/22/2019 at 7:42 AM, Strange said:

If large amounts of matter are falling into the black hole then, as far as we know, the interior will be full of that matter falling inwards. It will take a finite time for that matter to reach the centre, meanwhile more matter is continuously arriving. A waterfall is still full of water, even though it is free falling towards the ground.

Talking of waterfalls: A Black Hole is a Waterfall of Space

But what about an isolated black hole that is not feeding on anything?  Even if a few atoms should get captured, they would soon reach the singularity and there would remain a vacuum inside the event horizon.

[Strange]

26 minutes ago, Airbrush said:

But what about an isolated black hole that is not feeding on anything?  Even if a few atoms should get captured, they would soon reach the singularity and there would remain a vacuum inside the event horizon.

Just like outside. Not surprising.

(Of course, we don't know what is inside the event horizon. It could be uniformly full of chocolate.)

[Airbrush]

35 minutes ago, Strange said:

Just like outside. Not surprising.

How so?  I was thinking of space with an average density of about one atom per cubic meter.  Any few atoms that stray too close to the BH will get gobbled up in no time at all.  So that means that the region immediately inside the event horizon should be a perfect vacuum.  Unless the atoms that enter an isolated black hole bounce around inside?  Don't they head for the center and stay there?

Edited April 23, 2019 by Airbrush

[Strange]

55 minutes ago, Airbrush said:

How so?  I was thinking of space with an average density of about one atom per cubic meter.  Any few atoms that stray too close to the BH will get gobbled up in no time at all.  So that means that the region immediately inside the event horizon should be a perfect vacuum.  Unless the atoms that enter an isolated black hole bounce around inside?  Don't they head for the center and stay there?

If you have a steady arrival of particles entering and leaving (or reaching the singularity) I assume the average density of particles would be constant. And similar to that outside. But my intuition might be wrong there.