Evaporation Of A Black Hole

[Qfwfq]

...even if I believe something I will still question it to death. That is what science is about rather than saying "Accepted science is this, this and this. That's good enough for me." Thinking is allowed.

This is perfectly fair, as long as your critique makes sense and is based on competent reasoning. If you base it on arguments that have much less nexus than those you criticize, what's the point?

 

I myself don't consider Hawing radiation a 100% certainty nor even the existence of black holes as described by the usual models but that is another matter, I do however reason upon them along defendible lines. Therefore I don't agree with your critique at all and I don't deem it worthwhile to discuss, if you don't accept input which makes sense. I simply apply the same critical stance (that you recommend) to your arguments.

[maddog]

Maddog. We are all different.

Accepted. Your point?

 

Are you saying use imagination instead of experimentation? I can imagine elephants flying but that does not mean that science allows it.

Now you are being silly. Einstein used the same kind of thought problem by imagining that he could "ride" a

beam of light in attempting to come up with Special Theory of Relativity. Now are you in fact saying using a thought

problem to help to understand what is going on nature is inappropriate??? Every scientist/inventor since

Galileo has done this. It is as I said, quite normal and not out of the ordinary. What would you benefit imagining

a flying elephant when this is not what goes on in nature.

 

Magnetic fields of the sun heat particles to a million degrees where the surface is maybe 6,000.C. So we come to black holes where trillions of gauss whips streams of particles off into space at almost light speed, as in the jets from their poles. How is that irrelevant?

Irrelevant in that high magnetic flux or low magnetic flux - what falls in to a BH falls in. What does does.

 

At 0.K it is not “residual energy fluctuations”. Matter still exists as matter with electrons around protons and neutrons, etc. Back in 2003, MIT recorded temperatures as low as half a billionth of a degree above absolute. If temperature affected say electrons, slowing them down, then at very low temperatures, matter would begin to collapse in on itself.

Under no conditions what would this kind of collapse occur. To do so would be "very" classical.

 

My thinking is anything but classical.

Not based upon what you wrote above. Of course that is your claim. <_<

 

maddog

[sigurdV]

Accepted. Your point?

 

 

Now you are being silly. Einstein used the same kind of thought problem by imagining that he could "ride" a

beam of light in attempting to come up with Special Theory of Relativity. Now are you in fact saying using a thought

problem to help to understand what is going on nature is inappropriate??? Every scientist/inventor since

Galileo has done this. It is as I said, quite normal and not out of the ordinary. What would you benefit imagining

a flying elephant when this is not what goes on in nature.

 

 

Irrelevant in that high magnetic flux or low magnetic flux - what falls in to a BH falls in. What does does.

 

Under no conditions what would this kind of collapse occur. To do so would be "very" classical.

 

 

Not based upon what you wrote above. Of course that is your claim. <_<

 

maddog

 

I wonder where the rays coming from a quasar comes from, how they are generated... Do we know?

[CraigD]

I wonder where the rays coming from a quasar comes from, how they are generated... Do we know?

Yes, with about as much confidence as with any very distant astronomy hypothesis, and with a very great sense of diminished bafflement than when Hong-Yee Chiu coined the phrase “quasi-stellar” and the sort, catchy name “quasar” for them in 1964.

 

Present best wisdom is they’re very distant active galactic nuclei. AGNs are thought to be fairly short-lived (astronomically speaking – on the order of 10 to 100 million years) galaxies with a lot of matter falling toward its central super-massive black hole (the consensus now it that practically every galaxy has a central SMBH), getting swirled up in a gigantic, hot, tremendously luminous accretion disk. Eventually, all this radiation blows most of the infalling matter away from the CSMBH, “deactivating” the galactic nucleus and turning down its luminosity, which allows matter to begin infalling again, continuing a cycle that can IMHO nicely and poetically be described as “breathing”.

 

Because quasars are very distant, the radiation of them we’re now seeing is very old, and the AGN that produced it from a very young age of the universe, so they’re both very large galaxies, and very “loose matter” rich, giving rise to a very bright AGN compared to nearer ones that are on subsequent active phases of their active/inactive “breathing” lifecycles.

 

Back to the topic, Hawking radiation and black hole evaporation aren’t theoretically significant processes in quasars and other AGNs – though “black-hole powered”, AGNs are really just big hot, glowing gas clouds far enough away from their SMBHs that their physics are pretty ordinary, not the quantum weird kind of Hawking radiation.

 

I think it’s key in any consideration of Hawking radiation to keep in mind its power law: it’s proportional to the inverse square of their mass ([imath]P = \frac{k}{M^2}[/imath]). So the HR for supermassive, or even ordinary star-mass BHs, is very, very small. Hawking, and various later researchers have noted that this means HR, to borrow a phrase from Adam Helfer IMHO well-written 2003 paper Do black holes radiate, which Freeztar pointed us to in post #17, “not only has a quantum origin but is quantum in its presentation”, meaning its luminosity is so low, there should be long intervals between BHs emitting single particles of radiation.

 

I don’t think one can overstress the weirdness of such gigantic bodies having such low luminosities – in our ordinary physical experience, even for cold bodies, “size matters”, and large bodies have large luminosities. BHs don’t follow the intuitive rules of ordinary physics, but are, according to Hawking and the physics mainstream, very nearly, but not completely, truly black.

 

I also don’t think one can overstress that, despite HR being widely accepted, nearly every well understanding person who accepts it is also aware of many problems that could eventually lead to rejecting it. Helfer paper gives a pretty good outline of this, pointing out what I think is the main worry with HR: that it’s fundamentally a”semiclassical” one – that is, an uneasy marriage of necessity between classical mechanical General Relativity and quantum mechanics.

 

IMHO, the main beauty of HR is that it answers the “why aren’t there lots of little black holes?” paradox question simply and elegantly. When and if we ever have a good quantum mechanical theory of gravity, we may well completely discard Hawking’s work’s conclusions.

[jeremyb]

I was unable to follow most of the posts here, that is my fault though.

 

From what I did understand, please correct me if I am wrong:

 

a black hole takes a very long time to evaporate once there is nothing left for it to consume, and it does so one particle at a time.

 

This brings me to this question: A black hole that has consumed much of a decent sized solar system (with nothing left close enough to it for it to consume), how long would it take to evaporate? I am guessing it would take longer than the current age of our universe, if that holds true, I would then question again how a black hole losses mass. If that is false, I would need to understand the correct time cycle or mass loss rate of the aging black hole.

 

My apologies for not being able to follow much of the conversation.

[freeztar]

I was unable to follow most of the posts here, that is my fault though.

 

From what I did understand, please correct me if I am wrong:

 

a black hole takes a very long time to evaporate once there is nothing left for it to consume, and it does so one particle at a time.

 

This brings me to this question: A black hole that has consumed much of a decent sized solar system (with nothing left close enough to it for it to consume), how long would it take to evaporate? I am guessing it would take longer than the current age of our universe, if that holds true, I would then question again how a black hole losses mass. If that is false, I would need to understand the correct time cycle or mass loss rate of the aging black hole.

 

My apologies for not being able to follow much of the conversation.

 

No apologies needed...this stuff is heady...especially for us non-physics students...

 

The time a black hole takes to evaporate can be determined by T_ev. The critical factor is the event horizon diameter (or spheric volume).

 

The equations can be found here: http://en.wikipedia....ole_evaporation

 

If you need help with the math, please post back and someone can help you out.

 

For most Super-massive Black Holes, like those found at the center of galaxies, the evaporation time is *very long*. That is to say that they will be around long after this Solar System is dead and gone. Indeed, they have predicted rates of life that far exceed the current age of the universe. According to the wiki article linked above, " for a black hole of 10¹¹ kg, the evaporation time is 2.667 billion years". Given that the most massive of these strange bodies can exceed [math]10^{10}[/math] solar masses, then you can easily see that it will take billions of years for the most massive black holes to dissipate.

[CraigD]

This brings me to this question: A black hole that has consumed much of a decent sized solar system (with nothing left close enough to it for it to consume), how long would it take to evaporate?

Using the evaporation time formula is pretty easy. Here it is:

 

[math]t_{\text{ev}} = k M^3[/math]

 

The hardest part is evaluating the constant, [imath]k= \frac{5120 \pi G^2}{\hbar c^4}[/imath],in whatever units you want to use. For small black holes (which have never been certainly observed), [imath]k \dot= 8.408 \times 10^{-17} \,\text{seconds/kg}^3[/imath] is useful. For star-sized and bigger ones (which we have), [imath]k \dot= 2.097 \times 10^{67} \,\text{years/mass}_{\text{Sun}}^3[/imath] is good.

 

A star-remnant black hole that’s consumed the planets and other stuff around it – which isn’t to be expected, as the gravitational effect of a star and a black hole of the same mass on neighboring bodies are the same – massed about the same as one that hasn’t, as the mass of all the stuff around a star is just a small fraction of the mass of the star. So we can use our years and Sun mass unit constant and calculate

 

[math]t_{\text{ev}} = 2.097 \times 10^{67} \,\text{years/} M_{\odot}^3 \cdot (1 M_{\odot})^3 \, \dot= \, 2.097 \times 10^{67} \,\text{years}[/math]

 

[imath]2.097 \times 10^{67}[/imath] years is about a trillion trillion trillion trillion trillion times the present age of the universe, a pretty inconceivable long time. The evaporation calculation also assumes nothing’s falling into the black hole, not even starlight and background radiation, which can’t happen naturally until the universe is so old there are no more radiating stars, and expansion has reduced the background radiation to nearly zero. So, for all practical purposes, star mass and larger black holes don’t evaporate. When they do will be in the far, far future, deep cosmic time, the ultimate fate of the universe, the end of time, toward the end of the Black Hole Era or whatever phrase you prefer for that when.

 

A key point I’ve been trying to make in this thread is that the main usefulness of Hawking radiation is not calculating when ordinary black holes will evaporate in the far, far future, but calculating that small ones evaporate almost instantly, and thus explaining why we never observe and small ones.

[Cyberia]

Therefore I don't agree with your critique at all and I don't deem it worthwhile to discuss, if you don't accept input which makes sense.

 

Making sense is a relative position. If you don't agree with what I say, you don't think I make sense.

 

If you won't debate someone who does not make sense to you, as in someone who disagrees with you, do you actually debate with anyone or do you just agree with people who think as you do?

[Cyberia]

Maddog. Because we are all different, don’t expect me to think as you do.

 

The big bang relies on things that are no more than ideas to explain failings in it, like inflation and dark energy. It also relies on unproven ideas like space stretching infinitely without change. It does not have any credible origin. It is as credible as a flying elephant.

 

I would think Hawking Radiation needs a tranquil environment to work. A black hole is anything but tranquil. A variation: Imagine two particles of quantum closeness at the centre of an atomic explosion. One falls to the ground and the other flies off into space……

 

At so called absolute zero, molecular motion stops but atomic motion continues. This shows that more energy might be removed so lower temperatures could be possible.

 

Why let others do all your thinking for you. Just because something is in a book or on an internet site it does not mean that it is true.

 

Moderation note: replies to this and other posts involving a discussion of absolute zero have been moved to thread Discussion of absolute 0 from astronomy thread "Evaporation Of A Black Hole", because they are not about this thread’s main topic, black hole evaporation.

Edited February 27, 2012 by CraigD
Added moderation note

[Cyberia]

I wonder where the rays coming from a quasar comes from, how they are generated... Do we know?

 

Quasars are powered by black holes. Very energetic black holes at that as in lots of stuff falling into them so they give off hard radiation and lots of highly energetic particles which have escaped being swallowed.

[Cyberia]

We actually have no hard evidence for Hawking Radiation as this is an idea he came up with but he has previously discarded other ideas which originally seemed possible, like singularities, which most still continue to cling to. And of course the loss of information in a black hole.

 

I think Hawking would prefer that we think for ourselves rather than slavishly cling to his musings.

[maddog]

Making sense is a relative position.

Relative to what?

 

If you don't agree with what I say, you don't think I make sense.

I am not sure I agree. I may disagree with when you make sense or I may agree that you don't make any sense.

 

If you won't debate someone who does not make sense to you, as in someone who disagrees with you, do you actually debate with anyone or do you just agree with people who think as you do?

This one is a bit tough as in deliberate over a discussion towards making a point that might be

contrary to another implies that either side is comprehensible to the "other" side & visa versa.

Yes, a lot of your comments either lack this or are incomplete or inaccurate, making such a

discussion meaningless. <_< I think this is what CraigD and I are saying (though Craig don't let

me speak for you. You can chime in here).

 

maddog

[maddog]

Maddog. Because we are all different, don’t expect me to think as you do.

I don't expect you anything...

 

The big bang relies on things that are no more than ideas to explain failings in it, like inflation and dark energy. It also relies on unproven ideas like space stretching infinitely without change. It does not have any credible origin. It is as credible as a flying elephant.

Actually I find a flying elephant as a more credible than the diatribe about the Big Bang. Granted I don't have

same enthusiasm towards Dark Energy per se. I find this as a way similar to using epicycles in understanding

the orbit of planets around the sun.

 

I would think Hawking Radiation needs a tranquil environment to work. A black hole is anything but tranquil. A variation: Imagine two particles of quantum closeness at the centre of an atomic explosion. One falls to the ground and the other flies off into space……

Only in your mind. You stand alone.

 

At so called absolute zero, molecular motion stops but atomic motion continues. This shows that more energy might be removed so lower temperatures could be possible.

There is no "At ... absolute zero". The term is not an "achievable" value. It is a limit that can only

be approached. With today's technology we are approaching the range of MicroKelvins above Abs 0

(which 10e-6 Kelvins) and this is still greater than 0. Since this statement is incorrect any conclusion

you draw is incorrect. Garbage in - Garbage out. <_<

 

... Just because something is in a book or on an internet site it does not mean that it is true.

Or even posted by SextonBlake. :P

 

 

maddog

 

Moderation note: replies to this and other posts involving a discussion of absolute zero have been moved to thread Discussion of absolute 0 from astronomy thread "Evaporation Of A Black Hole", because they are not about this thread’s main topic, black hole evaporation.

Edited February 27, 2012 by CraigD
Added moderation note

[freeztar]

We actually have no hard evidence for Hawking Radiation as this is an idea he came up with but he has previously discarded other ideas which originally seemed possible, like singularities, which most still continue to cling to. And of course the loss of information in a black hole.

 

I think Hawking would prefer that we think for ourselves rather than slavishly cling to his musings.

 

I agree and celebrate your ideas of freedom from slavish thoughts. Nonetheless, I think Hawking deserves a bit more respect for his ideas.

 

It takes a stroke of genius to think about quantum separation. I agree that it is not perfect and leaves something to be desired. That doesn't mean the idea is invalid. Until there's a better explanation, it's the best we've got, no?

[maddog]

We actually have no hard evidence for Hawking Radiation as this is an idea he came up with but he has previously discarded other ideas which originally seemed possible, like singularities, which most still continue to cling to. And of course the loss of information in a black hole.

I think Hawking would prefer that we think for ourselves rather than slavishly cling to his musings.

Hawking has not "backpeddled" on Hawking Radiation (though maybe you would like to be so).

 

Where Hawking admitted that he had "erred" in his previous thinking and he now renounces is that a

BH can prevent leaking of information out. This was a discussion between he and Berkenstein (Jacob

I think). From this when he lost the bet, he bought Jacob "whatever" wanted upon which Berkenstein

said that he wished the Burns book on Baseball.

 

This was all on the Berkenstein Conjecture (look it up). This refers to the entropy of the Black Hole.

 

maddog

 

ps: I made it easier for you here is the link

Black Hole Thermodynamics

Edited February 23, 2012 by maddog

[Lancewen]

I found an interesting article in online PopSci that you all might be interested in. But it's one of the comments that I think applies to this thread and the concept of evaporation due to Hawking Radiation that I wish to share.

 

 

How to Take a Picture of a Black Hole

 

http://www.popsci.co...312&spPodID=020

 

cigarshaped

 

Thank you Clay, an unusually balanced article. Sadly it has become so common to hear that "the black hole is proven, case closed". Unfortunately so many eggs have been put into the Einstein basket that it is hard to see astronomers changing their minds - even if contradictory evidence is staring them in the face. More often than not the theory is adapted for each new contra data, rather than re-evaluating it.

 

I'm sorry but my impression of the Standard Model is no better than an adult fairy story. How anyone can believe in so many imaginary constructs which have no laboratory-testable properties, it's beyond me! I think we are doing our young scientists a disservice by insisting that little is left to discover. Mathematics is no longer a tool to explore sound ideas. It has become the means and end, far removed from reality.

 

Let's hope the truth will dawn, before funding ceases for these extravagant schemes of endeavor. I believe a far more integrated picture of the universe will eventually emerge. Showing a cohesion from subatomic to galactic scales, we will realize how our solar system is integral to an ever evolving circuit of energy. Importantly, a circuit that can change suddenly too.

 

"It's the thunderbolt that steers the universe!" Heraclitus, 5th century BC

[Cyberia]

I agree and celebrate your ideas of freedom from slavish thoughts. Nonetheless, I think Hawking deserves a bit more respect for his ideas.

 

The point is that it's idea from Hawking and not something he has shown to be true in a lab. Even Einstein had his off days like not being able to see through the double slit experiment.

 

 

It takes a stroke of genius to think about quantum separation. I agree that it is not perfect and leaves something to be desired. That doesn't mean the idea is invalid. Until there's a better explanation, it's the best we've got, no?

 

A flat world was all we had at one time, with god above and the devil below. Was that better than nothing?

 

The problem with such solutions as posited by Hawking is that people are willing to accept them because of who he is. If wrong, it has stopped people putting forth other possibilities that may be right.