Can black holes ever truly disappear?

[s4syth]

Assuming that space inside a black hole is expanding, just like regular space, could the density of a black hole be slowly lowered enough for the event horizon to dissapear, creating a supermassive ball of... stuff?

 

[pnjabiloafer]

well, i don't really understand your question, but i think i know what your asking. The density of a black hole is infinite, so i don't think you can actually lower it (maybe it can be lowered, we just don't know about it), and black holes are actually dissolving. As they turn, they are releasing Hawking's Radiation into space, and eventually, more radiation will be released, then the "stuff" that goes into the black hole.. and in millions of years, the black hole will "vaPOOrise" and nothing will be left of them. hope this helped, ;-]

 

[berty]

What do you make of Stephen Hawking 'alleged' about turn on the theory of black holes, ie:- that information absorbed by them is not necessarily destroyed as he previously believed?

 

[selfAdjoint]

Let's wait till he makes his speech. There'll be plenty of postings here when that happens.

 

[pnjabiloafer]

yeah, he is supposed to make a quantum gravity theory i beleive. I haven't really been following things lately. I don't think everyone will accept his ideas, i guess we'll have to wait and see.

 

[Hurkyl]

Actually, black holes generally aren't very dense at all, if you take the volume to be the space inside the event horizon. The thing about an evaporating black hole is that it stays a black hole until the bitter end, and the emitted stuff is perfectly randomly scattered about.

 

[Imparcticle]

I never understood just how virtual particles are separated from their partners when approaching the event horizon. Anyone care to explain?

 

[selfAdjoint]

Take a location somewhere close to, but above the event horizon of the black hole. Imagine that the energy in the highly stressed (tightly curved) spacetime causes a virtual pair of particles to climb from virtual state to reality here. By conservation of momentum they have opposite momenta. So if one momentum has a component toward the horizon then the other one has a component away from the horizon. Thus the "away" one can escape while the "toward" one falls in.

 

[Imparcticle]

Imagine that the energy in the highly stressed (tightly curved) spacetime causes a virtual pair of particles to climb from virtual state to reality here.

How does that happen? what classifies a "real" particle from a "virtual" particle?

 

[selfAdjoint]

Virtual particles have just temporary small amounts of energy that lead them to "bloom and die" in too short a time for them to be observed. That's how they can get that energy, they are essentially "kiting" it off the conservation books, which only have to be balanced with observable fluxes of energy. In the math, the virtual particles' mass comes out imaginary, which is telling us they can't be seen. They are said to be "off the mass shell."

Real particles have positive real mass and their momentum and energy is conserved.

Now if you have a flux of energy from some source into the quantum vacuum, it can contribute real, conservable energy to the virtual pairs and promote them to real particles. The tension of tightly curved space near a black hole can do that.

 

[s4syth]

Infinite?

How can a black hole's density be infinite? I don't see how that would, or could happen. Is there not a maximum density limit? And also, infinite density would mean infinite mass and energy, wouldn't it? I realize that some singularities occur in black holes, but does that make them infititely dense?

 

[Chronos]

Best explanation I know of is the Planck density limit [which is incredibly high, but finite]. I am comfortable with that until something better comes along. I can accept mathematical singularities. They merely suggest we haven't found the right solution.

 

[Phobos]

Welcome to Physics Forums, s4syth!

Assuming that space inside a black hole is expanding, just like regular space, could the density of a black hole be slowly lowered enough for the event horizon to dissapear, creating a supermassive ball of... stuff?

The gravity of a black hole overwhelms the expansion force. Our galaxy is not expanding because of the gravity holding it together. The expansion of space only becomes significant over the huge inter-galactic distances where gravity is low.

 

[Phobos]

How can a black hole's density be infinite? I don't see how that would, or could happen. Is there not a maximum density limit? And also, infinite density would mean infinite mass and energy, wouldn't it? I realize that some singularities occur in black holes, but does that make them infititely dense?

density = mass/volume

A black hole singularity, at least as modeled by general relativity, is some finite mass compressed to a point.

(infinite density = finite mass over zero volume)

 

[urtalkinstupid]

singularity

The idea of a singularity is being ruled out by many scientists today. They now turn their attention to strings that have a length called "plancks length." There is no such thing as infinite. Infinite is just a hyperbole expressing some quantity that is large. Something can have large mass not infinite mass. A black hole only has as much mass as the neutron star it was condensed from, but different density. It does not have infinite density, but its density is very large. Gases that are being accelerated in the ergosphere collide are heated up and produce gammma rays and x-rays. The collision of these particles give spawn to particle/anti-particle pairs. This also accounts for the vast amounts of radiation that are said to be around a black hole, because when a particle and anti-particle encounter one another, they are said to annhilate each other creating EM energy. The black hole is not really losing mass. None of this particle/anti-particle pairing takes place inside the event horizon. Hey, I could be wrong. If I am, please let me know.

Hope this helps.

Forgot to add. The only reason why these strings are said to have zero volume is because they are one dimension consiting of a length.

volume = lxwxh
volume = lx0x0
volume = 0