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Author Topic: Stupid Black Hole question !  (Read 3100 times)

Offline neilep

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Stupid Black Hole question !
« on: 07/08/2006 14:04:36 »
Is there any eventuality at all that one could imagine where a black hole may lose it's ' black-hole-ness ' and revert to being what ?..a neutron star perhaps ?

Could there be a possibility where a body is almost...almost becoming a black hole and fluctuates between the two states ?

I think I know the answer that once a black hole...always a black hole ?

...but...is there any circumstance one can imagine ?..how ever bizarre it is, but in theory may be a possibility ?...even the remotest one ?

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another_someone

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Re: Stupid Black Hole question !
« Reply #1 on: 07/08/2006 14:23:16 »
quote:
Originally posted by neilep
Is there any eventuality at all that one could imagine where a black hole may lose it's ' black-hole-ness ' and revert to being what ?..a neutron star perhaps ?

Could there be a possibility where a body is almost...almost becoming a black hole and fluctuates between the two states ?

I think I know the answer that once a black hole...always a black hole ?

...but...is there any circumstance one can imagine ?..how ever bizarre it is, but in theory may be a possibility ?...even the remotest one ?



I think the first issue that will raise its head is Hawkins radiation, which is a way for black holes to lose energy (at least in theory no-one has seen it it practice but then, no-one has even seen a black hole for fairly obvious reasons they are black).



George
 

another_someone

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Re: Stupid Black Hole question !
« Reply #2 on: 07/08/2006 15:04:46 »
quote:
Originally posted by neilep
Could there be a possibility where a body is almost...almost becoming a black hole and fluctuates between the two states ?



I am actually still trying to work out how something can become a black hole not that it cannot be so, but by what process.

Clearly, it is possible to conceive of a situation where mass exists that is so dense as to create an event horizon around it the problem is how does the transition between the non-existence and the existence of this event horizon come about?

http://en.wikipedia.org/wiki/Event_horizon#Interacting_with_an_event_horizon
quote:

A misconception about event horizons, especially black hole event horizons, is that they represent an immutable surface that destroys objects that approach them. In practice, several features are common to all event horizons: they appear to be some distance away from any observer, objects sent towards an event horizon never appear to cross it from the sending observer's point of view (as the horizon-crossing event's light cone never intersects the observer's world line).



(my emphasis)

Thus, if an object is never seen to fall into an event horizon from the perspective of an outside observer, then how will anything ever get within a black hole from the perspective of an outside observer (all the outside observer would see is things piling up on the boundary of the black hole although where this boundary might lie may be different for different observers).



George
 

Offline Mjhavok

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Re: Stupid Black Hole question !
« Reply #3 on: 07/08/2006 15:34:27 »
To answer your question I have thought about it and came up with this answer.









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Offline neilep

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Re: Stupid Black Hole question !
« Reply #4 on: 07/08/2006 15:55:16 »
THANK YOU SO MUCH for your insights GEORGE and STEVEN...Hawkins radiation eh ?..I must check it out . Wiki here I come (5 mins later) interesting stuff...but as soon as wiki displayed the formulas I lost the plot...in fact I lost in it a black hole !!...very interesting about the event horizon phenomena.....perhaps my crazy idea of somehow being able to make something  ' out of phase  ' would be useful here, it would not be effected by the gravity pull and therefore it's light would be visible and would be able to enter a black hole as easy as intricate science goes in one of my ears through empty space and out the other !!:)

STEVE....your answer is above and beyond the call of duty....THANK YOU

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another_someone

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Re: Stupid Black Hole question !
« Reply #5 on: 07/08/2006 16:16:32 »
My rather crude understanding of Hawkins radiation amounts to that when there is a massive tension in space created by gravity (i.e. the gravity at one point is very much stronger than the gravity at a nearby point), then matter will spontaneously be created by tension in gravity.

Move directly, matter and anti-matter can be spontaneously created anywhere and everywhere, but normally they are only created for an unmeasurable short period of time, and then they destroy each other.  Because of the very short time they exist, they cannot be measured, and so in practice cannot be seen to exist.  When placed under intense gravitational tension, it can pull apart the matter and the anti-matter, and one half falls into the black hole, and the other half radiates into space.

But, in creating this matter/anti-matter pair, energy has to be used by the black hole.  If the matter/anti-matter pair then annihilate each other, the energy can be recovered by the black hole.  If the pair are pulled apart so that they cannot annihilate each other, then the energy is permanently lost to the black hole.

That is my idiots understanding of Hawkins radiation no doubt Ian will make mincemeat of it.

Incidentally, Hawkins radiation related to a phenomena called the Unruh effect :

http://en.wikipedia.org/wiki/Unruh_effect
quote:

The Unruh effect, discovered in 1976 by Bill Unruh of the University of British Columbia, is the prediction that an accelerating observer will observe black-body radiation where an inertial observer would observe none. In other words, the accelerating observer will find themselves in a warm background. The quantum state which is seen as ground state for observers in inertial systems is seen as a thermodynamic equilibrium for the uniformly accelerated observer.
Unruh demonstrated that the very notion of vacuum depends on the path of the observer through spacetime. From the viewpoint of the accelerating observer, the vacuum of the inertial observer will look like a state containing many particles in thermal equilibrium a warm gas.


The existence of Unruh radiation can be linked to this apparent event horizon, putting it in the same conceptual framework as Hawking radiation. On the other hand, the Unruh effect shows that the definition of what constitutes a "particle" depends on the state of motion of the observer.






George
 

Offline Soul Surfer

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Re: Stupid Black Hole question !
« Reply #6 on: 09/08/2006 19:29:40 »
Quiet black holes of any size (say bigger than the mass of the sun )are extremely "cold"  because the gravitational tensions at their event horizon are relatively low when it comes to creating photons or other particles to generate the Hawking radiation.  They are in fasct cooler than the current level of the microwave background radiation and are therefore always getting bigger by absorbing the microwave background radiation even if there is nothing else around to fall into them.  The bigger they are the colder they get.  When the universe eventually gets very cold they will start to evaporate very slowly and will take many orders of magnitude longer than the universe has existed to go away  so to answer the question once a black hole always a black hole.  That is of course assuming that the current theories about blackholes are valid.

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Re: Stupid Black Hole question !
« Reply #6 on: 09/08/2006 19:29:40 »

 

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