PDA

View Full Version : How would object with radius a bit larger than its Schwarzschild radius behave?



WaxRubiks
2008-Oct-19, 11:22 AM
How would an object that appeared just a bit larger than the blackhole and event horizon it would form behave?

Would it be that much different to the black hole it would form?

Wouldn't the time dilation at its surface be very large, and wouldn't object that fell towards it behave similarly to those approaching an event horizon?

Wouldn't it create a lens effect in a similar manner?

Would it emit radiation similarly to Hawking radiation?

Would it be possible to tell the difference between said object and an event-horizon black hole?

KingNor
2008-Oct-19, 02:19 PM
Hmm... I think the question might be a little flawed. Let me see if i got this right:


The Schwarzschild radius (sometimes historically referred to as the gravitational radius) is a characteristic radius associated with every mass. It is the radius for a given mass where, if that mass could be compressed to fit within that radius, no known force or degeneracy pressure could stop it from continuing to collapse into a gravitational singularity. The term is used in physics and astronomy, especially in the theory of gravitation, general relativity.

If I understand this correctly, I think that means that any object that isn't being crushed down to a singularity is an object that extends past it's Schwarzchild Radius.. so.. the earth, you, me, the sun. We're all objects you describe.

Another slight problem is that with gravity, everything is sorta scaled.. so any object or objects with the same mass will behave gravitationally similar if you back away enough. A solar mass black hole would let planets orbit it the same way our sun does.

I tried to answer 2 of your questions with my limited knowledge and assumeing what you meant was if an Object extended past it's own event horizon. i tried at least :doh:



Would it be that much different to the black hole it would form?

I don't think so, asside from the behavior of blackhole singularities, there isn't much special about the way black holes' gravity works. like they said a while back on astronomy cast: we'd orbit a solar mass black hole the same way we'd orbit the sun. I have no idea what would happen to the actual mass at the horizon if it extended past the event horizon though. there would have to be enough solid mass below the horizon to hold up the mass outside, with out the singularity devouring the object from the inside out.


Wouldn't the time dilation at its surface be very large, and wouldn't object that fell towards it behave similarly to those approaching an event horizon?

I think this depends entirely on the raw mass of the gravity of the object, and it's effect on time dilation. I think an object falling towards this thing would behave exactly the same as an object falling towards a similar sized black hole, with one exception instead of falling into the event horizon and being doomed to the singularity, the object would land on the surface of this thing. The gravity maybe is still big but an outside observer would still be able to see it.

TobiasTheViking
2008-Oct-19, 02:41 PM
Nothing of what i state is dogma, this is how i think it is, but i'm not a phycisist, so maybe someone will correct me.


How would an object that appeared just a bit larger than the blackhole and event horizon it would form behave?
Pretty much like a very dense neutron star...


Would it be that much different to the black hole it would form?
It wouldn't really be that close to a black hole, in quite a few ways.


Wouldn't the time dilation at its surface be very large, and wouldn't object that fell towards it behave similarly to those approaching an event horizon?
There would be time dilation at the surface, but then again, there is that at the surface of all objects(just very small). i'm not sure how big it would be. Objects that fell towards it would only behave similarly to objects approaching the event horizon of a black hole, in that they would time dilate more when getting close, and it would be harder to get away the closer you are(which is also true for the sun.. the time dilation might be so small as to make no real difference, as is the case with the sun)


Wouldn't it create a lens effect in a similar manner?
Again, everything with gravity creates a lens effect, it might be extremely tiny, so tiny that it can't actually be measured, but it will be created.

Whole galaxies create lens effects. Again, nothing to do with a black hole, just gravity.


Would it emit radiation similarly to Hawking radiation?
Hawking radiation is caused by matter and anti-matter being created on each side of the even horizon, the part outside the event horizon will fly off, the stuff inside will be stuck. If there is no even horizon, the two will colide and become nothing...
So no hawking radiation without an even horizon.


Would it be possible to tell the difference between said object and an event-horizon black hole?
Yes, it would emit(or reflect) light. so it would be quite visible.

grant hutchison
2008-Oct-19, 02:59 PM
Yes, it would emit(or reflect) light. so it would be quite visible.The surface of this object would also light up like a flare under the impact of any infalling material, which would strike it with a velocity close to lightspeed. Whereas no such effect would occur at the event horizon of a black hole; infalling material just disappears from view.
That's one of the ways we could differentiate between a black hole with an accretion disc and some other massive object with an accretion disc.

Grant Hutchison

TobiasTheViking
2008-Oct-19, 03:32 PM
Ah, quite correct, i missed that rather logical conclusion.

WaxRubiks
2008-Oct-19, 05:25 PM
well, I mean an object that might only be a few centimeters, or meters bigger than the Schwarzschild radius black hole.



Yes I thought of the reflection too; but if all the matter that falls into a black hole never appears to reach or pass the event horizon, wouldn't light reflect off that infalling matter too?

Hornblower
2008-Oct-19, 05:50 PM
If an object is just slightly larger than the Schwarzschild radius for the same mass, any light from its surface would be gravitationally redshifted, and a clock on its surface and viewed from afar would appear to be very slow.

m1omg
2008-Oct-19, 07:18 PM
I guess because of this it wouldn't be very bright, I would imagine it a perfect (with no surface freatures due to stupendously large surface gravity) dark red faintly glowing ball, with distorted background around it due to light bending gravity.

grant hutchison
2008-Oct-19, 09:10 PM
Yes I thought of the reflection too; but if all the matter that falls into a black hole never appears to reach or pass the event horizon, wouldn't light reflect off that infalling matter too?But not in the same way.
The redshift goes to infinity at the horizon for both free-falling material and for a static surface, but everywhere short of the horizon you get a different (greater) redshift for the infalling material than for the static shell.
You're also not going to see a flare from a surface impact if you drop something into a black hole event horizon, since a later infaller can't catch up with earlier infalling material.

Grant Hutchison

Nereid
2008-Oct-19, 09:36 PM
I assume that, in the OP, you are referring to some ideal object, for the purposes of getting answers that focus on GR - is that correct?

AFAIK, an object just a tad bigger than its Schwartzchild radius would collapse, quickly, to form a black hole, over any range of mass for which GR+SM seems valid, today. The only examples of such an object are collapsars (massive stars with iron cores that go endothermic) and merging/colliding neutron stars, though maybe an accreting neutron star could get there too. The appearance of any of these would be dominated by the rapid changes afoot - the collapse, merger, collapse - rather than the nuances of near-event horizon effects and Hawking radiation.

But as collapses and mergers leading to BHs have been modelled, in all their GR glory, perhaps reading up on some of those models would answer your quesitons Fm? Would a reference or two to those be of help do you think?

WaxRubiks
2008-Oct-19, 11:12 PM
but maybe there is a mechanism to prevent collapse, post neutron star.

I don't have much faith in BHs "modelled, in all their GR glory", as models can be wrong, and computers just do what their told, not read the mind of God.

grant hutchison
2008-Oct-19, 11:18 PM
but maybe there is a mechanism to prevent collapse, post neutron star.

I don't have much faith in BHs "modelled, in all their GR glory", as models can be wrong, and computers just do what their told, not read the mind of God.So what's the point of the question? Any answer that comes within a few centimetres of the event horizon requires GR in pretty much full pomp. You're going to believe it a centimetre outside the event horizon, but not a centimetre inside?

Grant Hutchison

WaxRubiks
2008-Oct-19, 11:32 PM
Well, I do believe that GR models can produce useful results, but I don't necessarily believe that the models are necessarily valid models for what actually happens to objects.

If you see what I mean...


Anyway, I don't see anything wrong with discussing such an object.


I trust GR models up to a point, but I don't believe in the event horizon as a real phenomenon.

I think the GR models define the limits to what can happen, but the universe always finds ways to stay ahead of those limits.

So, just outside the limit, I trust the results for time dilation etc.

Van Rijn
2008-Oct-19, 11:47 PM
I trust GR models up to a point, but I don't believe in the event horizon as a real phenomenon.


What is it about the event horizon that you don't believe? What's your "physically real" alternative that matches observations (http://www.bautforum.com/1345682-post98.html)?

slang
2008-Oct-19, 11:51 PM
I trust GR models up to a point, but I don't believe in the event horizon as a real phenomenon.

Could you elaborate on what you mean by "real phenomenon"?

Does "real phenomenon" mean you can poke it with your finger and know it's there? Or could the term "real phenomenon" be satisfied by a certain boundary condition, in the sense that it might be the limit of where one "force is equal or stronger than another force"? Is the point between the Moon and Earth where their gravities 'tug' with equal force on a spacecraft a "real phenomenon"?

WaxRubiks
2008-Oct-19, 11:55 PM
well, I think the event horizon, is a bit like the "edge of the Earth" idea that people had before they found out the world was a sphere.


My "physically real" alternative is that from the point of view of the infalling matter, that is just what it is; infalling matter, with all its angular momentum, charge, mass etc, probably mainly neutrons, I don't know. But from the outside, the matter that is infalling looks much larger, to preserve the measurable speed of light, maybe to keep the uncertainty value valid; and what you appear to have is a ball of matter, just bigger than the Schwarzschild radius.

I'm hoping that somehow Hawking radiation, or something similar, will still work, with this idea; or else the collapsing matter will collapse forever, which I don't think would happen.

Still that is all a bit off topic.
I just want to know if scientists could tell the difference between black holes and objects slightly larger.

WaxRubiks
2008-Oct-19, 11:58 PM
Could you elaborate on what you mean by "real phenomenon"?

Does "real phenomenon" mean you can poke it with your finger and know it's there? Or could the term "real phenomenon" be satisfied by a certain boundary condition, in the sense that it might be the limit of where one "force is equal or stronger than another force"? Is the point between the Moon and Earth where their gravities 'tug' with equal force on a spacecraft a "real phenomenon"?

by real phenomenon, I mean a described volume of space, from which light cannot escape.
And by "real" I suppose I mean that it would be possible to gather strong evidence for this happening.

Van Rijn
2008-Oct-20, 12:01 AM
by real phenomenon, I mean a described volume of space, from which light cannot escape.
And by "real" I suppose I mean that it would be possible to gather strong evidence for this happening.

I know you've seen this before. (http://adsabs.harvard.edu/abs/2008NewAR..51..733N) Is there some reason you don't consider this to be strong evidence?

grant hutchison
2008-Oct-20, 12:02 AM
Well, I do believe that GR models can produce useful results, but I don't necessarily believe that the models are necessarily valid models for what actually happens to objects.

If you see what I mean...


Anyway, I don't see anything wrong with discussing such an object.OK. So we've established above that there are differences, predicted under GR, between an event horizon and a static surface just outside the event horizon.
And we know that these differences can in principle be observed here on Earth (in particular, the result of stuff falling inwards and either impacting a surface or reaching an event horizon).
And we know (via references given in a recent post (http://www.bautforum.com/1343710-post8.html) by Tim Thompson), that we have observations which match an event horizon rather than a surface.

So that all seems pretty clear to me.

Grant Hutchison

WaxRubiks
2008-Oct-20, 12:20 AM
well, I don't understand this, from the quote by Van Rijn, which is the same one linked to by Grant Hutchinson.


The black holes are on average observed to be fainter by a factor of ˜100–1000. The natural explanation is that a neutron star must radiate the advected thermal energy from its surface, whereas a black hole can hide the energy behind its event horizon

How can a black hole hide energy behind its event horizon, given that matter is never seen to cross it?

Is it just the radiation that crosses it?
If so, how does it get passed all the infalling matter?

grant hutchison
2008-Oct-20, 12:45 AM
How can a black hole hide energy behind its event horizon, given that matter is never seen to cross it?

Is it just the radiation that crosses it?
If so, how does it get passed all the infalling matter?If it hits a surface just outside the event horizon, it hits that surface in finite time, and produces energy equivalent to the kinetic energy of an object moving near lightspeed. A large amount of radiant energy is produced.

For an event horizon, whether the infalling object ever crosses the event horizon is just a matter of coordinates: for an observer falling along with the object, it crosses the event horizon in finite proper time and its kinetic energy disappears inside the black hole; for a distant observer, the object never crosses the event horizon, but it never catches up with any of the matter falling ahead of it either, and so it never undergoes an impact that converts its kinetic energy. No radiant energy is produced, either way.

Big (and detectable) difference.

Grant Hutchison

WaxRubiks
2008-Oct-20, 01:07 AM
But the distant observer is all that matters in terms of detecting what happens to stuff falling towards a black hole, isn't it?


Anyway this object that I propose, IS in a state of collapsing, so I'm not sure whether stuff would impact a surface, and even if it did there would be a big redshift to any radiation coming off.

Anyway any object just larger than the Schwarzschild radius black hole would also have a big redshift.


And anything falling onto an object a few centimeters larger than the Schwarzschild radius black hole, would take a long time time impact.


I think that it would take more than the luminosity result for infalling matter to prove there was an event horizon.


There was that Feynman quote in someone's sig about not fooling yourself, and yourself being the easiest person to fool.
I think that the existence, or not, of the event horizon is an important question, but since it is a difficult subject people just want to steam ahead as if its existence has definitely been proved.

grant hutchison
2008-Oct-20, 01:11 AM
But the distant observer is all that matters in terms of detecting what happens to stuff falling towards a black hole, isn't it?Yep. No energy released for a distant observer, as I said.


Anyway this object that I propose, IS in a state of collapsing, so I'm not sure whether stuff would impact a surface, and even if it did there would be a big redshift to any radiation coming off.So it's going to be a black hole soon, then?


Anyway any object just larger than the Schwarzschild radius black hole would also have a big redshift.But different from the redshift exhibited by objects falling into a black hole.


And anything falling onto an object a few centimeters larger than the Schwarzschild radius black hole, would take a long time time impact.But not an infinite time.


There was that Feynman quote in someone's sig about not fooling yourself, and yourself being the easiest person to fool.Well, we've got evidence.
What do you have? :)

Grant Hutchison

Nereid
2008-Oct-20, 01:20 AM
but maybe there is a mechanism to prevent collapse, post neutron star.
Maybe there is ... but it hasn't been discovered yet, and in the Q&A section wild speculation is out of bounds.



I don't have much faith in BHs "modelled, in all their GR glory", as models can be wrong, and computers just do what their told, not read the mind of God.
You are, of course, not required to have faith in BHs, GR, physics, science, ... or invisible pink fairies, at least not in this Q&A section.

Here, IMHO, we are limited to discussion of mainstream astronomy (and cosmology and physics), so all anyone can do to answer your questions is to point you towards papers reporting the results of GR modelling exercises, and papers which comment on those (etc). If you think you have found some shortcomings in those (beyond those stated in the papers themselves), or have some better models, why not write up a paper or two and submit for publication?

More fundamentally, you seem to have not understood the points Ken G (and others) have made, dozens and dozens of times, in a great many BAUT posts, about the scope of physics (or science in general) and what its relationship to 'reality' is.

WaxRubiks
2008-Oct-20, 01:26 AM
evidence? you mean data?

evidence implies an interpretation of the data. Where as I can interpret it another way and it is MY evidence, so there. :P

anyway, I would say your evidence is pretty flimsy; I wouldn't want to send a man to prison based on that level of evidence.

The trouble with the black hole idea is that it has become a cultural paradigm, so it is hard for people to give the idea up; still I'm betting they will have to eventually; unless the world's economy collapses and then we can all go back to believing in fairies. :)

Van Rijn
2008-Oct-20, 01:32 AM
evidence? you mean data?

evidence implies an interpretation of the data. Where as I can interpret it another way and it is MY evidence, so there. :P


So, since you seem not to be interested in the answers, then as Grant asked earlier, what's the point of these questions? After all, they are repeats of questions you already asked in "Fun for GR fans" and elsewhere, and have already been discussed elsewhere as well.

WaxRubiks
2008-Oct-20, 01:33 AM
Maybe there is ... but it hasn't been discovered yet, and in the Q&A section wild speculation is out of bounds.


I think I was asked to explain why I asked the question.

I think that the OP question is perfectly ok for the Q&A section; why not.

To say that just because there is no known mechanism to stop further collapse means that I shouldn't ask a simple question; is a bit catch 22 ish.

How would one discover a mechanism unless one speculated about such objects.

The OP was a simple question; all I was looking for where GR based answers. I don't think people should have to justify why they post astronomy based questions in Q&A; and if asked to explain their position a bit more thoroughly, they should not be accused of "wild speculation", even if it is wild speculation, they were only answering a question.
Did you contribute an answer to the OP question? I can't remember.

WaxRubiks
2008-Oct-20, 01:45 AM
So, since you seem not to be interested in the answers, then as Grant asked earlier, what's the point of these questions? After all, they are repeats of questions you already asked in "Fun for GR fans" and elsewhere, and have already been discussed elsewhere as well.


yes, I am a bit biased; what's wrong with that; but do you say I am not interested in "the" answer because I don't automatically believe it?
Do you think people should automatically believe things, base on the fact that someone says something or because it is on a website?

All I am doing is questioning some of the answers, is that too difficult to cope with?



Maybe some ATMers are right, that science, to some is a bit like a religion, with its priests, whom only can read the sacred texts and must be believed.

Get Steven Hawking in here right now, if he says it, then yes I will recant all my sins and believe in the big test tube in the sky again. :D

Van Rijn
2008-Oct-20, 01:56 AM
yes, I am a bit biased; what's wrong with that; but do you say I am not interested in "the" answer because I don't automatically believe it?


I don't think it is reasonable to waste our time repeating the same questions if you aren't interested in the answers. So I ask again: What's the point of these questions?



All I am doing is questioning some of the answers, is that too difficult to cope with?


If you want elaborations of answers, that I could understand. But that doesn't seem to be what you want.

WaxRubiks
2008-Oct-20, 02:05 AM
I don't think it is reasonable to waste our time repeating the same questions if you aren't interested in the answers. So I ask again: What's the point of these questions?



well that's a bit odd for a science forum.

I dunno, perhaps we could talk about the weather.

Van Rijn
2008-Oct-20, 02:15 AM
Can't or won't answer the question? By the way, the repeat question issue is discussed in this thread:

http://www.bautforum.com/about-baut/80164-wearing-down.html

Nereid
2008-Oct-20, 02:17 AM
[...]

I think that the OP question is perfectly ok for the Q&A section; why not.
Those questions were pretty much answered by post#3 (though there were some elaborations a bit later with a few details that are relevant to the clarification(s) you wrote a little later), at least in a non-technical form.

To what extent do you think the OP questions were not answered, or inadequately answered? Would you like some references to material in which the technical details are presented?




To say that just because there is no known mechanism to stop further collapse means that I shouldn't ask a simple question; is a bit catch 22 ish.
Nothing wrong with the question - it's actually a good one! :) - but what to do with the answer?

Saying "assume there is a mechanism to stop further collapse, what happens in that case?" doesn't much help ... if only because the details of any such mechanism would likely enter into the answer in a big way.


How would one discover a mechanism unless one speculated about such objects.
This is (another) very good question, especially if re-phrased in a form that addresses where ideas come from in astrophysics ... but surely not pertinent to this thread, or even (perhaps) this section of BAUT (or even BAUT at all)?



The OP was a simple question; all I was looking for [were] GR based answers.
[...]
Do you feel you have got them ("GR based answers")?

WaxRubiks
2008-Oct-20, 06:34 AM
Do you feel you have got them ("GR based answers")?


yes, sort of.


I just wanted to hear people's different views;

I looking for definitive answers in Q&A, sometimes you get them, but I have started to think that that is a bit naive to treat Q&A as the font of all knowledge;
Perhaps all one can often hope for in these sorts of threads is to get some sort of insight into a problem.

grant hutchison
2008-Oct-20, 11:22 AM
I looking for definitive answers in Q&A, sometimes you get them, but I have started to think that that is a bit naive to treat Q&A as the font of all knowledge;That's so obviously true that I doubt if anyone here would dispute it.


Perhaps all one can often hope for in these sorts of threads is to get some sort of insight into a problem.Trouble is, what we seem to be seeing is:
1) Frogmarch asks a question about black holes.
2) Frogmarch receives detailed answers supported by references.
3) Frogmarch ignores all content that contradicts his own ideas.
4) Frogmarch then makes one or several ATM claims concerning black holes.
5) Frogmarch repeats the process.

To an outside observer, the "insight" bit seems sadly lacking.

Grant Hutchison

Neverfly
2008-Oct-20, 11:57 AM
The march of the frogs is circular.

WaxRubiks
2008-Oct-20, 12:02 PM
yes, this isn't an entirely false characterisation. :D

But I wouldn't say I ignored the content; although I am biased towards my own idea sightly, but aren't we all?

I have changed my views over the weeks;

I really didn't want to make an ATM claim in this thread, but I was asked about mechanisms that would prevent further collapse. Maybe, in future, I will just say that the answer would be ATM and not answer.

Nereid
2008-Oct-20, 01:09 PM
[...]

I looking for definitive answers in Q&A, sometimes you get them, but I have started to think that that is a bit naive to treat Q&A as the font of all knowledge;
:)

The scope of the Q&A section is, indeed, limited ... to what those who write (in answer to questions) understand about contemporary, mainstream astronomy, astrophysics, cosmology, space science, etc.

I'm sure there are examples of questions not answered that could have been, in the sense that there's some aspect of mainstream astronomy not known to BAUT members who read this section (and try to answer questions), but IMHO there won't be very many ... collectively BAUT members who post answers here have an astonishingly broad understanding of modern astronomy.

More common, then, are replies to the effect 'that's not within the scope of astronomy' or 'that's an open question today'.


Perhaps all one can often hope for in these sorts of threads is to get some sort of insight into a problem.
Which is a pretty wonderful outcome, don't you think? :)

Sure saves you years of potentially fruitless research working on your own, eh?

John Mendenhall
2008-Oct-20, 04:50 PM
4) Frogmarch then makes one or several ATM claims concerning black holes.

Grant Hutchison

Grant hits the crux of the problem here. If you want to present alternatives to the mainstream, do it in ATM. Posting and arguing ATM ideas in Q&A wastes the time of some very capable people who spend lots of time answering legitimate questions in Q&A. If you don't like the current black hole model - and you are not alone, myself included - then you should propose an alternative in ATM and be prepared to defend it. And to take some lumps.

Within current mainstream ideas and possible in the real world, consider this: a massive object, hovering on the edge of gravitational collapse, say a neutron star, is impacted by a large object. What happens next? What will we observe?

Notice, that there is plenty of room for fireworks and speculation within the mainstream.

Regards, John M.

nauthiz
2008-Oct-20, 05:34 PM
Hawking radiation is caused by matter and anti-matter being created on each side of the even horizon, the part outside the event horizon will fly off, the stuff inside will be stuck. If there is no even horizon, the two will colide and become nothing...
So no hawking radiation without an even horizon.

I wish I could find the reference, but I'm coming up broke. . .

Last summer I saw a paper that looked at the case of an object whose boundary was only outside its event horizon by an infinitesimal amount (just a few angstroms, I believe). They predicted, among other things, that the object would produce radiation that looked very much like Hawking radiation, but through a different mechanism.

I got the impression that the paper was basically saying that such an object would be very hard to distinguish from a black hole for a distant observer because it would produce all the phenomena that we currently use to infer the presence of a black hole. It also might not ever become a black hole because it could evaporate quickly enough that the Schwarzschild radius was always just inside the object's outside boundary.

timb
2008-Oct-20, 08:36 PM
AFAIK, an object just a tad bigger than its Schwartzchild radius would collapse, quickly, to form a black hole, over any range of mass for which GR+SM seems valid,

Not if it was below the critical Tolman-Oppenheimer-Volkoff mass. In that case it would be expanding, quickly. How a body below that mass would ever get so small is another question. :shifty:

nauthiz
2008-Oct-20, 08:39 PM
Not if it was below the critical Tolman-Oppenheimer-Volkoff mass. In that case it would be expanding, quickly. How a body below that mass would ever get so small is another question. :shifty:
Cue LHC doomsday discussion in 5. . . 4. . . 3. . .

Van Rijn
2008-Oct-20, 08:45 PM
I wish I could find the reference, but I'm coming up broke. . .


Any idea where you saw this? A web page? Something more significant?



They predicted, among other things, that the object would produce radiation that looked very much like Hawking radiation, but through a different mechanism.
[snip]
It also might not ever become a black hole because it could evaporate quickly enough that the Schwarzschild radius was always just inside the object's outside boundary.

On the face of it, that seems to be a bit of a problem. Hawking radiation is essentially irrelevant for stellar mass black holes (it only becomes significant for much smaller black holes). So if there is a hypothetical, rapidly evaporating, stellar mass object, how could it look like Hawking radiation? Actually, from the description, it sounds like it would be a very luminous object, which would not be very much like a black hole.

publius
2008-Oct-20, 09:00 PM
Last summer I saw a paper that looked at the case of an object whose boundary was only outside its event horizon by an infinitesimal amount (just a few angstroms, I believe). They predicted, among other things, that the object would produce radiation that looked very much like Hawking radiation, but through a different mechanism.



My guess is that would be Mitra's (et. al) MECO/ECO notion. The idea there was the cold collapse model was flawed and radiation pressure would actually stave off collapse. You'd have a very compact object that had essentially converted all its mass to radiation and was *SLOWLY* radiating it away. It would be all but indistinguishable from a black hole, save for a tiny amount of "hair".

Thanks to some detailed info from those who know far more about this that I ever will, I've pretty much discounted the MECO idea now. Mitra and his proponent made some pretty silly errors in GR. One was Mitra was claiming that nothing could free fall into an existing Schwarszchild black hole (this is apart from the question of whether one could really form, a "pre-existing" black hole is valid EFE solution) in its own proper time. Then there was some nonsense about what we call the Schwarzchild solution was actually wrong, etc, etc.

The other big killer with me was there is an exact solution of the EFE, the Vaidya null dust solution I believe its called, that models a collapsing "ball of radiation", a shell of null dust, into a black hole. So there you have pure radiation collapsing, which just killed the MECO radiation pressure thing with me. I now pretty much conclude that Mitra and his people don't know what they're talking about. :)


-Richard

nauthiz
2008-Oct-20, 09:02 PM
Any idea where you saw this? A web page? Something more significant?
Heh, just remembered I found it because it was written up on Bad Astronomy, that makes it easier.


Vachaspati, Tanmay; Stojkovic, Dejan; Krauss, Lawrence M. "Observation of incipient black holes and the information loss problem". Physical Review D, vol. 76, Issue 2, id. 024005 (2007)

Here's a arXiv's copy. (http://arxiv.org/PS_cache/gr-qc/pdf/0609/0609024v3.pdf)

TobiasTheViking
2008-Oct-21, 08:43 PM
I swear, if you were any more dense, you'd fall within your own Schwarzschild radius, become a black hole, and we wouldn't have to deal with you anymore.

WaxRubiks
2008-Oct-21, 11:35 PM
I swear, if you were any more dense, you'd fall within your own Schwarzschild radius, become a black hole, and we wouldn't have to deal with you anymore.


Is that addressed to anyone in particular?

TobiasTheViking
2008-Oct-21, 11:48 PM
Actually no, found it on /. and thought it was funny.

SagoSans
2008-Oct-22, 06:53 AM
I swear, if you were any more dense, you'd fall within your own Schwarzschild radius, become a black hole, and we wouldn't have to deal with you anymore.

Anyway, that's a keeper :lol: - it's a pity that it can't be used on BAUT :silenced:

TobiasTheViking
2008-Oct-22, 11:45 AM
Indeed is a keeper

John Mendenhall
2008-Oct-29, 05:19 PM
I swear, if you were any more dense, you'd fall within your own Schwarzschild radius, become a black hole, and we wouldn't have to deal with you anymore.

There is a difference between 'no information can escape from', and 'no useful information has ever escaped from'. :)

nauthiz
2008-Oct-29, 05:26 PM
There is a difference between 'no information can escape from', and 'no useful information has ever escaped from'. :)

Ah. The essential difference between black holes and the Internet.

TobiasTheViking
2008-Oct-31, 10:21 PM
There is a difference between 'no information can escape from', and 'no useful information has ever escaped from'. :)
hehe


Ah. The essential difference between black holes and the Internet.
bahaha