Black Hole

[THX1138]

There are pictures on this site that purport to be to be “ I believe “ jets of matter emanating from the poles of black holes that are feeding / eating more than they handle.
Where is the event horizon if this is happening, not on the poles?

[Chris Peterson]

There are pictures on this site that purport to be to be “ I believe “ jets of matter emanating from the poles of black holes that are feeding / eating more than they handle.
Where is the event horizon if this is happening, not on the poles?

The event horizon of any black hole is a spherical surface of some radius, which is determined by the mass of that black hole.

Jets are unrelated to the event horizon. They are streams of material which has fallen inward from an accretion disc and is ejected along the polar axes. That material never reaches the event horizon, so it isn't lost to the black hole. Jets can be produced by rotating bodies other than black holes, as well.

[saturno2]

Stephen Hawking, in his book History of Time, wrote:
" So, the only place to put this black hole ( primitive ), so that we can
to use the energy it emits, would in orbit around the Earth, and the only way
that it could be put into orbit would trapping by great mass set before
him, similar to the carrot in front of the donkey "

[Chris Peterson]

Stephen Hawking, in his book History of Time, wrote:
" So, the only place to put this black hole ( primitive ), so that we can
to use the energy it emits, would in orbit around the Earth, and the only way
that it could be put into orbit would trapping by great mass set before
him, similar to the carrot in front of the donkey "

He's talking about primordial black holes with masses on the order of 10⁹ tons, which are massive enough to have not quite yet evaporated, but low enough mass to be hot. Of course, such objects have never been observed and may not exist. But if the do, they will be outputting several gigawatts of energy in the form of x-rays and gamma rays. This is what he says, in his original language:

One such black hole could run ten large power stations, if only we could harness its power. This would be rather difficult, however: the black hole would have the mass of a mountain compressed into less than a million millionth of an inch, the size of the nucleus of an atom! If you had one of these black holes on the surface of the earth, there would be no way to stop it from falling through the floor to the center of the earth. It would oscillate through the earth and back, until eventually it settled down at the center. So the only place to put such a black hole, in which one might use the energy that it emitted, would be in orbit around the earth - and the only way that one could get it to orbit the earth would be to attract it there by towing a large mass in front of it, rather like a carrot in front of a donkey. This does not sound like a very practical proposition, at least not in the immediate future.

[saturno2]

Chris Peterson
You are right
Yes, this is the original text.
Stephen Hawing talks about the " Primordial Black Holes" ( Chapter 7 )

[Chris Peterson]

If the jet material does not reach the Black Hole why would any other material reach the black hole? Does the black hole say, 'Okay, you're welcome, but your friend isn't?'

That's about it. The history of any given particle around a black hole depends on how it interacts with other particles. Material will either be in an open or closed orbit until it becomes dense enough to lose energy through momentum transfer processes (such as collisions). Material that loses enough energy will fall into the black hole. Material that gains energy (as jet material does) will be ejected from the system before reaching the event horizon.

Even material that falls into the black hole is in orbit- unfortunately for it, that orbit just happens to have a periapsis inside the radius of the event horizon.

[saturno2]

Stephen Hawing in his book " History of Time", wrote
" Anything or anyone who falls through the event horizon ( of a black hole)
will soon reach the region of infinite density and the end of time"
I don´t understand the infinite density.
If matter has infinite density, would be so small and it disappear in the
space

[Chris Peterson]

Stephen Hawing in his book " History of Time", wrote
" Anything or anyone who falls through the event horizon ( of a black hole)
will soon reach the region of infinite density and the end of time"
I don´t understand the infinite density.
If matter has infinite density, would be so small and it disappear in the
space

Hawking is just speculating. Wildly. There is no physical theory that describes the interior of a black hole.

[Markus Schwarz]

Hawking is just speculating. Wildly. There is no physical theory that describes the interior of a black hole.

The interior of a black hole, excluding the "center", is described by general relativity. Of course, since the interior is hidden by the event horizon, it will be forever hidden from us experimentally.

"Anything or anyone who falls through the event horizon ( of a black hole)
will soon reach the region of infinite density and the end of time"
I don´t understand the infinite density.
If matter has infinite density, would be so small and it disappear in the
space

The whole "infinite density" at the "center" of a black hole is the reason why general relativity breaks down at the black hole's "center". The "infinite density" leads to a so-called singularity, which can, in a mathematically strict sense, be described as a "hole" in spacetime. I guess this is what Hawking refers to as the "end of time".
A common believe is that once you take the quantum mechanical nature of matter at high densities into account the "infinite density" is replaced by a meaningful expression. Unfortunately, a full theory of quantum gravity is not known.

[Chris Peterson]

Hawking is just speculating. Wildly. There is no physical theory that describes the interior of a black hole.

The interior of a black hole, excluding the "center", is described by general relativity. Of course, since the interior is hidden by the event horizon, it will be forever hidden from us experimentally.

When I said interior, I was actually thinking center. That said, however, I don't know many people who believe that GR describes the center, and probably the majority of physicists think it breaks down well before the center, including at the event horizon. I stand by my comment that Hawking's statement is very speculative.

I'm not certain that the interior of a black hole will remain forever hidden from us, except in the most literal way. Theories that describe the interior are likely to have observable ramifications outside the interior. Much of nature is directly hidden from us, which hasn't stopped us from achieving deep understandings.

[Markus Schwarz]

I'm not certain that the interior of a black hole will remain forever hidden from us, except in the most literal way. Theories that describe the interior are likely to have observable ramifications outside the interior. Much of nature is directly hidden from us, which hasn't stopped us from achieving deep understandings.

We agree on that point. If we had an experimentally verified theory of quantum gravity we would most likely solve the singularity problem as well and know about all of the interior of a black hole. This brings me to your other point:

That said, however, I don't know many people who believe that GR describes the center, and probably the majority of physicists think it breaks down well before the center, including at the event horizon.

We both agree (I assume) that general relativity describes physics outside the event horizon. Therefore, we can use it to calculate what happens as a particle falls into a black hole. Since nothing special happens for the particle at the event horizon (it reaches it in finite proper time, finite tidal forces, etc.) I don't see why general relativity should not be valid there. The same is true shortly behind the horizon. This is standard textbook physics. Hawking, Penrose and others put all of this on a solid mathematical basis in the framework of general relativity. Of course, things get more murky the closer you get to the center. Usually, one assumes vacuum conditions, but this is likely not true since the matter that formed the black hole is likely still around. A not too speculative thing to say IMHO would be that general relativity breaks down inside the black hole when the vacuum condition is no longer satisfied. Of course, the point at which this happens is impossible to tell right now, but from what I said above, I doubt it is at the event horizon.

[Chris Peterson]

Of course, things get more murky the closer you get to the center. Usually, one assumes vacuum conditions, but this is likely not true since the matter that formed the black hole is likely still around. A not too speculative thing to say IMHO would be that general relativity breaks down inside the black hole when the vacuum condition is no longer satisfied. Of course, the point at which this happens is impossible to tell right now, but from what I said above, I doubt it is at the event horizon.

I also agree that it probably isn't the event horizon. But that's the first point where things get murky. The problem (which you allude to) is that we don't understand how actual matter behaves under extreme compression. So as we near the center, it's likely (but not certain) that matter assumes some sort of as yet undescribed exotic state. That could allow GR to work just fine by eliminating the singularity problem. But right now, we can't know for certain. Which is why I think it's important to emphasize that any discussion about what goes on inside a black hole is necessarily speculative. (I didn't look up the original reference Saturno was quoting; I believe he's using a non-English edition of Hawking, and there have been some translation issues in the past.)

[saturno2]

Stephen Hawing in his book " History of Time", wrote
" Anything or anyone who falls through the event horizon ( of a black hole)
will soon reach the region of infinite density and the end of time"
I don´t understand the infinite density.
If matter has infinite density, would be so small and it disappear in the
space

History of Time by Stephen Hawing in lenguage original ( No translation)
Chapter 6 after of a phrase of the poet Dante.

[Chris Peterson]

History of Time by Stephen Hawing in lenguage original ( No translation)
Chapter 6 after of a phrase of the poet Dante.

Keep in mind that this idea of a singularity- a point of infinite density- is a mathematical conclusion, not necessarily a physical one. There may be no such singularity in the center of a black hole; indeed, I think the majority of physicists would probably think there is not. Of course, our inability to visualize or intuit a physical phenomenon is not evidence that phenomenon is poorly understood. Nature is under no obligation to be obvious to humans.

BTW, with respect to "the end of time" in the Hawking quote, I think he's just making a reference to his comment a few paragraphs earlier that the singularity in the black hole is rather like the singularity assumed at the start of the Big Bang, which he calls the "start of time".

[THX1138]

How a teaspoon of anything can weigh ten tons or more and what infinite density would even be like / A teaspoon of matter being ???? A million tons???? I live for this stuff, I just love reading about it

[Markus Schwarz]

How a teaspoon of anything can weigh ten tons or more and what infinite density would even be like / A teaspoon of matter being ???? A million tons???? I live for this stuff, I just love reading about it

The matter density inside the nucleus of an atom is about a billion tons per teaspoon (~10^9 T/cm^3). But the radius of whole atom is about hundred thousand times larger, giving an average density of about 1 gram per teaspoon (roughly the density of materials on Earth). In a neutron star, gravity is so strong that the electrons are pressed into the nucleus, turning the protons into neutrons. The entire star is just a tightly packed collection of neutrons (hence the name) with a density of nuclear matter. If the density is even stronger, no force we know of can withstand gravity and the neutron star collapses and forms a black hole.

According to general relativity matter would then be compressed at infinitum inside the black hole. But most physicist do believe that the laws of gravity and/or quantum mechanics are no longer valid at these ultra high densities. Once we know what theory replaces general relativity and/or quantum mechanics likely the whole problem with infinite densities will be solved.

[THX1138]

I imagine a good percentage of the brightest minds on this planet are trying to solve this problem as we speak. The world needs another Einstein of sorts to come along as I really hope these questions are answered before I’m gone or that is, go the way of all flesh.

BTW, Germany! Well that's a good few miles down the road from here, I've got some relatives in Hamburg ( Otto and Erna ) Some of the nicest people you could ever meet.
Thanks for your comment, Mike 5ive out

[Chris Peterson]

I imagine a good percentage of the brightest minds on this planet are trying to solve this problem as we speak. The world needs another Einstein of sorts to come along as I really hope these questions are answered before I’m gone or that is, go the way of all flesh.

Actually, I expect only a tiny, tiny percentage of the brightest minds on this planet are working on that particular problem!

And curiously, we don't seem to actually need "Einsteins". While quite a few "big ideas" of science are associated with individual geniuses, the reality is that ideas have their time. All of the stuff that Einstein came up with was floating out their among scientists. Einstein was first, he knocked a few years off the puzzle, but had Einstein not existed, we'd be at a similar state of knowledge today. The same applies to other big ideas. And that's good. We don't need to wait for the random genius. Just lots of smart people doing good work and sharing it.

[saturno2]

I think that:
Physical infinite density is a variable that moves to vacumm, matter disappear.
physical density has a limit.
A black hole contains matter wich tends to limit density and it is his
maximum value.

[saturno2]

I think ( posibility ) that before the Big Bang, existed a Super
Black Hole, wich the matter had low temperature and high
density. It passing the limit of maximum density, the matter
exploded ( Big Bang) with the power of thousands of
bombs H .
It released a huge amount of head and energy, the matter was
expanded in all directions with a significant initial speed.

[Chris Peterson]

I think ( posibility ) that before the Big Bang, existed a Super
Black Hole, wich the matter had low temperature and high
density. It passing the limit of maximum density, the matter
exploded ( Big Bang) with the power of thousands of
bombs H .
It released a huge amount of head and energy, the matter was
expanded in all directions with a significant initial speed.

In terms of our current understanding, time began with the BB. So the concept of "before" the BB is complex, if not completely meaningless.

Also, matter is not moving apart. It is the space containing the matter that is expanding.

[saturno2]

saturno2 wrote:
It released a huge amount of HEAD and energy
Error head
Correct < heat >

[saturno2]

I agree with Chris Peterson, is better left alone the
Big Bang theory and her singularity as it is today.
I think mainly because ( this theory) has a
strong underlying theological load.
In the light of new Knowledge will change the
theorical framework of the Big Bang.

[MargaritaMc]

Just to note that the following thread is about black hole theory
http://asterisk.apod.com/viewtopic.php?f=8&t=32821

[bystander]

[url=http://fakescience.org/post/78027172019/black-hole-questions][size=150][b]Black Hole Questions[/b][/size][/url] [size=120][b]Fake Science | 2014 Feb 27[/b][/size]

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