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Author Topic: Another black hole question  (Read 3695 times)

Offline Fuzzy Logic

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Another black hole question
« on: 12/08/2006 00:27:07 »
Ok correct me if i am wrong on any of this.  My understanding of a black hole is that it is the desnly packed remains of a dead star,  the gravitational pull of which is so great that nothing can escape it.  My question is this,  is it really a hole?  or just a very dense little blob of matter called a hole because thats what it appears to be when looked at thru a 'scope.


 

Offline lightarrow

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Re: Another black hole question
« Reply #1 on: 13/08/2006 13:59:44 »
It's called "hole" because everything goes near it is pulled in and, if you approaches it too much (event horizon), you are "sucks" in, like inside a sink's hole, without any possibility to escape. It's called "black" because not even light can escape from inside the event horizon of it.
 

Offline socratus

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Re: Another black hole question
« Reply #2 on: 13/08/2006 14:27:00 »
An absolutely black body is a hypothetical body that
completely absorbs all the radiation falling on it.
Physicists said: “No such body can exist.“
2.
Black hole, is a region of space which no radiation
can be run away from it.
3.
The Absolute Zero: T=0K is a region of space
in which the motion of radiation died.
4.
But Planck said that from absolutely black body
a quantum of light can radiate.
5.
But Hawking showed that black holes can emit radiation.
6.
And the quantum theory said that in Vacuum there is
“ virtual motion of particles”  and they can radiate.
7.
Maybe absolutely black body and black holes are
only models of region of Absolute Zero space:  T=0K.
==================    
Is it really nobody see what model of "absolutely black body"
and model of "black holes" are identical
and they both describe  Vacuum ?
 

Offline Mjhavok

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Re: Another black hole question
« Reply #3 on: 14/08/2006 03:21:54 »
A black hole is a region of spacetime from which matter and energy cannot escape; in origin, a star or galactic nucleus that has collapsed in on itself to the point where its escape velocity exceeds the speed of light. Its boundary is known as the event horizon: light generated inside the event horizon can never scape. Black holes are believed to exist on all mass scales. Some binary stars which strongly emit X-rays may have black hole companions.
« Last Edit: 17/08/2006 05:34:18 by Mjhavok »
 

Offline Atomic-S

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Re: Another black hole question
« Reply #4 on: 14/08/2006 06:01:22 »
A proper understanding of black holes requires that we look at general relativity. General relativity tells us not only that everything within a certain radius is drawn irretrievably (we think) into it, but that the very space and time in the vicinity are seriously distorted. In fact, that can be taken as the very definition of gravity. In particular, time runs slower (as seen by an outside observer) near the black hole, and stops entirely at the event horizon. Space is also distorted -- I believe that a ruler in the direction of the gravity is shortened (as seen by an outside observer?) (Maybe someone can clarify this). The implications of this are that the laws of geometry as we ordinarly know them break down near a black hole. In particular, it would seem that the distance from one side of a black hole to the other (that is, from one side to the other of a mathematical sphere located ouside of the event horizon), as measured by laying a tape measure from the one side to the other through the black hole, is not equal to the circumfrence divided by pi, but is something quite different, possibly infinity, much in the same way as when you measure from one side of the mouth of a mine shaft to the other, by laying the ruler along the walls of the shaft, and find that the distance is far greater than the conventional distance acress the mouth.  If that is so, then we would be justified in declaring that a black hole is indeed a hole, geometrically speaking, in every sense of the word. Perhaps it is a tunnel leading off into some other dimension.

Related to this question is what happens to the geometry of a sphere surrounding the event horizon. Normally, the laws of spherical geometry state that the integral over the surface of the sphere, of the product of the eigencurvatures of each area element, times the size of the element, equals 2 pi steradians.  But when a black hole is inside the sphere, that may not be true any more.
 

another_someone

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Re: Another black hole question
« Reply #5 on: 14/08/2006 07:35:36 »
quote:
Originally posted by lightarrow
It's called "hole" because everything goes near it is pulled in and, if you approaches it too much (event horizon), you are "sucks" in, like inside a sink's hole, without any possibility to escape. It's called "black" because not even light can escape from inside the event horizon of it.



Not at all my understanding.

As I understand it, it is true that once you are inside the event horizon (which itself is a complicated issue), then there is no escape, but without the event horizon, the pull is no greater than for any other object of the same mass (i.e. a star of a certain mass will have a certain gravitational pull, and that pull will be the same whether the star is an ordinary star, if whether it is a black hole – but for an ordinary star, if you get too close, you will crash into the surface of the star, whereas if the star has collapsed into a black hole, it will have shrunk, so there is no surface to crash into, so you keep on going, but once you get to the event horizon (which is smaller than the ordinary size of the star), there is no way back).

It is a black hole because it not even light can escape from within the event horizon, and so there is no direct way of seeing it – it is black.

The issues around what an event horizon is, and where it is, seem to be quite complicated (either that or my understanding of it is just too weak – and it is in any case very weak).

As I understand it, the distortions of space and time around a black hole means that you never actually pass through the event horizon, you just keep approaching it, but never quite get there.  This would, to my mind, imply that the position (and by inference, the radius) of an event horizon changes depending upon your proximity to it.



George
 

Offline lightarrow

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Re: Another black hole question
« Reply #6 on: 16/08/2006 14:33:05 »
quote:
Originally posted by Atomic-S
...the integral over the surface of the sphere, of the product of the eigencurvatures of each area element, times the size of the element, equals 2 pi steradians.  But when a black hole is inside the sphere, that may not be true any more.


It's more than or less than 2 pi? Can this be the prove of the fact that space-time must fold itself on another dimension?
 

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Re: Another black hole question
« Reply #6 on: 16/08/2006 14:33:05 »

 

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