Center of below galaxy should have instantly become a BH. But the fact is that no star can become BH; And the reason is simple.

Core of any star is hottest and the pressure there is maximum; hence the explosive nuclear fusion reaction should first start in the center of a dieing massive star. Hence all the matter will flung out in a supernova leaving no BH and paving the way for the next generation of stars. And the universe continues in a steady state form. :)

The below pic shows that when billions of stars come in contact with each other, they keep on exploding and merging, again and again, shining bright like a giant star while converting mass into energy.

Just try comparing the size of the central object with the tiniest specs of the ring which are in fact stars.

http://sciforums.com/showpost.php?p=162071&postcount=1


http://antwrp.gsfc.nasa.gov/apod/image/0209/hoag_hst.jpg

Hoag's Object: A Strange Ring Galaxy
Credit: R. Lucas (STScI/AURA), Hubble Heritage Team, NASA

Is this one galaxy or two? This question came to light in 1950 when astronomer Art Hoag chanced upon this unusual extragalactic object. On the outside is a ring dominated by bright blue stars, while near the center lies a ball of much redder stars that are likely much older. Between the two is a gap that appears almost completely dark. How Hoag's Object formed remains unknown, although similar objects have now been identified and collectively labeled as a form of ring galaxy. Genesis hypotheses include a galaxy collision billions of years ago and perturbative gravitational interactions involving an unusually shaped core. The above photo taken by the Hubble Space Telescope in July 2001 reveals unprecedented details of Hoag's Object and may yield a better understanding. Hoag's Object spans about 100,000 light years and lies about 600 million light years away toward the constellation of Serpens. Coincidentally, visible in the gap (at about one o'clock) is yet another ring galaxy that likely lies far in the distance.

Beautiful pic! As I recall, Einstein didn't believe that black holes existed; he thought something physical (as opposed to theoretical) prevented it. Future theorists came to the conclusion that implosion to a singularity is mandatory under certain conditions; i.e. they believe that nothing physical prevents implosion under certain conditions. The issue is covered in chapter five of Black Holes & Time Warps.

There need not be an explosion at all, even at the core. According to the theory (general relativity), the only condition required for implosion is a minimum amount of mass in a given volume (a minimum density). So, for example, adding just a gram of matter to the surface of a star might make it implode to a singularity.

In your pic, the density of the central ball of stars may be below the minimum required for implosion. And the density isn't changing much because the stars are in stable orbits around the center, rather than falling toward the center.

Beautiful pic! ....

There need not be an explosion at all, even at the core. According to the theory (general relativity), the only condition required for implosion is a minimum amount of mass in a given volume (a minimum density). So, for example, adding just a gram of matter to the surface of a star might make it implode to a singularity.....

And what stops nuclear fusion at the stars center from blowing the star SuperNova before the implosion ?

I hope u heard about MegaNova.

Can someone except me explain the gap between the central object and the ring?

And what stops nuclear fusion at the stars center from blowing the star SuperNova before the implosion ?
The center wouldn't know the implosion was happening until it happened there. It would occur from the outside inwards. When the critical gram is added to the star, the surface would begin falling toward the center. Relative to an observer hovering at the former surface, the surface would instantly begin falling at the speed of light. Hence it must keep falling and can never rise (explode outwards), otherwise the outward speed of the matter would need to exceed the speed of light, which is impossible (so the theory postulates). And the center wouldn't know about the implosion until it happened there, because the surface is falling at the same rate as information flows. (For a better explanation, search Black Holes FAQ (http://cosmology.berkeley.edu/Education/BHfaq.html#q3) for "The horizon has some very strange geometrical properties".)

I don't believe this implosion occurs, mind you. I think it's malarkey. I'm just paraphrasing what the theory says.

I hope u heard about MegaNova.
There are so many trademarks on that name, it's hard to find a decent link about it. What is it, or can you provide a link?

Core of any star is hottest and the pressure there is maximum; hence the explosive nuclear fusion reaction should first start in the center of a dieing massive star. Hence all the matter will flung out in a supernova leaving no BH and paving the way for the next generation of stars. And the universe continues in a steady state form. :)


By the time a massive enough star reaches the point of producing a supernova, its core is composed of iron. Iron does not produce energy when it undergoes fusion, in fact it takes a net input of energy for iron to undergo fusion.

On top of the iron is a layer of silicon followed by, in order; oxygen, neon, carbon, helium and finally hydrogen.

Each of these layers take more and more heat and pressure to undergo fusion as you work inward towards the core, and each produces less energy through fusion.

The star collaspse when the iron core has grown large enough that it can no longer support its own weight (remember, there is no heat producing Fusion occuring at the core to help support it.) The core collaspes and the above layers fall inward to take up the space vacated by it. This collaspe causes explosive fusion of the outer layers. Some of the material form this explosion will tbe thrown outward, and some will be pushed inward towards the core, the latter will add to the mass of the core, and if after all is said and done, you get a neutron star, or, if the remainging core is massive enough, a black hole.

...On top of the iron is a layer of silicon followed by, in order; oxygen, neon, carbon, helium and finally hydrogen. ...I have a lot of respect for your knowledge in this area, and certainly that is the accepted theory / result of the ASSUMPTION that the dying star (when a significant amount of the core region is iron) looks that way, but I think it is more complex that the spherical symmetry model predicts. Also almost all nebulae exhibit a very asymetric aspect, such as even the tiny Crab nebulae.

I present my arguments in the thread, "Dark matter - what is it?" I hope you wil find time to take a look there and comment. As there have been 80 replies, I guide your attention to posts 61 and 63. BenTheMan and I have been exchanging ideas about my suggestion that the iron region is not likely to be at the exact mass center when it starts to collapse to the first of many much smaller black holes in a "chain reaction” of black hole formation as the shock wave from that "first to collapse" compresses other more central parts of the star above the critical conditions for black hole formation. (The second stage of the chain reaction.) The multitude of shock from these second stage collapses converge on less central parts of the star (from two or more sides) and form small regions with the critical density to collapse, even though they may be only neon etc. This is the third and final stage of black hole formation as the star is coming apart by this time. - The basic physics that starts the asymmetric chain reactions is that the fusion rate only depends quadratically on the density but exponentionally upon the temperature and statistical fluctuations in temperature, do exist. Thus are near central spots with very slightly increased fusion rates that make a self accelerating thermal instability and trigger the near center, but not usually at center, first collapse when they are mostly iron.
(The density is low just before they collapse, and the radiation pressure is quite significant. I sometimes call this region the “radiation bubble” and when fusion to iron stops, the much denser regions around the radiation bubble radially implode.


One of the other posts gives following link to a photo of the "Eskimo" nebula, which I also discuss in detail, identifying the one more distant "headless comet" at 3:30 O-clock as the first of (the three stage) black hole to form.

http://apod.nasa.gov/apod/ap031207.html

Please look at it also, if you have not already, especially useful if both it and the last part of post 63 can be seen on your screen at the same time. Thanks.

Can someone except me explain the gap between the central object and the ring?
it seems pretty obvious to me that a large cloud of matter coalesced into the galaxy you see at the center. subsequently, that mass of stars compressed (by radiation) the remaining matter in the cloud, which eventually got dense enough to form stars. that explains why the center has older stars and the outer ring has newer ones.

there are also some other explanations, but I think that is the most plausible.

it seems pretty obvious to me that a large cloud of matter coalesced into the galaxy you see at the center. subsequently, that mass of stars compressed (by radiation) the remaining matter in the cloud, which eventually got dense enough to form stars. ....


Seems like u just told us the reason why the universe is having acceleration in expansion or may be even the reason of the expansion itself;
bye bye BigBang.

....

On top of the iron is a layer of silicon followed by, in order; oxygen, neon, carbon, helium and finally hydrogen.

Each of these layers take more and more heat and pressure to undergo fusion as you work inward towards the core, and each produces less energy through fusion.

The star collaspse when the iron core has grown large enough that it can no longer support its own weight (remember, there is no heat producing Fusion occuring at the core to help support it.) ....

Thanks, thats the best SuperNova explanation i ever read.

But i doubt that the core is not hot, the core always hottest; even earth has a very hot core, i wonder if theres fusion in the earths center ? :cool:

...

I don't believe this implosion occurs, mind you. I think it's malarkey. I'm just paraphrasing what the theory says.


There are so many trademarks on that name, it's hard to find a decent link about it. What is it, or can you provide a link?

I think i confused HyperNova with meganova,
http://science.nasa.gov/newhome/headlines/ast21oct98_1.htm

any Negative vibes from this are purely accidental, but what about the black holes we have already seen? What are those then I ask.

Singularity will no doubt tell you, Positron, that the evidence for black holes is circumstancial. While this is technically correct, there still exists no way to explain xray spectra that we see in certain regions of space, or the gamma ray bursts that we see all over the sky. (Consider that we have never observed macroscopic evolution, but only the Creationists doubt the validity of the theory.)

Einstein's equations are perfectly happy with black holes---they are just singular at the origin. This is completely expected, as GR is a classical theory and is expected to break down anyway at very small distances. The presence of a black hole solution has nothing to do with the consistency of GR. Any claims to the contrary are made by people who don't understand GR, and/or by lunatics who are easily offended and have their own pet theories to pimp.

Hope this helps.

Core of any star is hottest and the pressure there is maximum; hence the explosive nuclear fusion reaction should first start in the center of a dieing massive star. [QUOTE]

You should study the life cycles of stars more closely. Fusion at the star's core is the process that keeps the star shining---once a star uses its supply of hydrogen, the fusion reaction can no longer occur, and the core becomes unstable.

[QUOTE]Hence all the matter will flung out in a supernova leaving no BH and paving the way for the next generation of stars. And the universe continues in a steady state form.

Again this is untrue, unless you are proposing an alternative. The inner core collapses and the outer core expands---because the temperature is dropping the color of the star goes from white to red. The inner core contracts and expells the outer gasses (conservation of momentum). If the inner core is massive enough, it becomes a black hole. Otherwise it turns in to a brown dwarf.

Thanks, thats the best SuperNova explanation i ever read.

But i doubt that the core is not hot, the core always hottest;
But with an Iron core , all of theat heat is due to pressure, and none of it due to energy released due to fusion. In fact, as I pointed out, the Fusion of Iron takes a net input of energy. If the Iorn core fused, it would actually suck energy from the star and speed the collaspe of the core.
even earth has a very hot core, i wonder if theres fusion in the earths center ? :cool:

It takes a body no smaller than 1/10 the mass of our sun to produce enough temp and pressure to maintain even hydrogen fusion. The Earth is magnitudes too small to generate the needed temp and pressure for that, let alone those needed to get our iron core to fuse. So, no, there is no fusion occuring at the Earth's core.

... While this is technically correct, there still exists no way to explain xray spectra that we see in certain regions of space, or the gamma ray bursts that we see all over the sky...

I think u need to learn to cut the crap.

U can learn a lot from Janus58 on how to do that. Look at your words and look at her selection of words, do u see any hostility there ?

Well , i am learning a lot form her, in terms of knowledge and manners too.:p

any Negative vibes from this are purely accidental, but what about the black holes we have already seen? What are those then I ask.


http://sciforums.com/showpost.php?p=1309922&postcount=9

The hotter an object is, the more radiation in the blue end of the spectrum it emits. More massive stars tend to be hotter since they burn their fuel faster. Main sequence stars are classified by their spectral type . hotter to cooler they go:

O:30,000 - 60,000K Blue stars
B:10,000 - 30,000K Blue-white stars
A:7,500 - 10,000K White stars
F: 6,000 - 7,500K Yellow-white stars
G: 5,000 - 6,000K Yellow stars (like the Sun)
K: 3,500 - 5,000K


I think after the blue stars we should get XRay stars.

http://hubblesite.org/newscenter/archive/releases/1998/07/text/



Janus58, u say that Iron fusion needs more energy that it can output, I dont know why its like that. Secondly, how come Uranium and other radioactive substance are used to create nuclear energy ?

If the star is collapsing then it will reach the Uranium stage due to fusion and being radioactive it should explode like a nuclear bomb.

I think after the blue stars we should get XRay stars.

http://hubblesite.org/newscenter/archive/releases/1998/07/text/



Janus58, u say that Iron fusion needs more energy that it can output, I dont know why its like that.
It has to do with the binding energy holding the nucleus together.
Secondly, how come Uranium and other radioactive substance are used to create nuclear energy ?
Uranium and other radioactive elements produce energy by fission IOW, they go from heavy Elements to lighter elements, while fusion goes from lighter to heavier. Again, Iron( Iron 56 to be precise) is the at the bottom of this energy ladder. Once you get there you can no longer produce energy by fission or fusion.

If the star is collapsing then it will reach the Uranium stage due to fusion and being radioactive it should explode like a nuclear bomb.

By this point, the pressure is so great that it actually pushes the electrons and protons ito each other forming neutrons, the core losses all elememtal properties and just becomes a mass of neutrons. Even if uranium could be produced, the intense pressure would prevent it from undergoing Fission.

I think u need to learn to cut the crap.

U can learn a lot from Janus58 on how to do that. Look at your words and look at her selection of words, do u see any hostility there ?

If you call crap anything that completely shoots down your theory, then I think you are in for a crap filled existence. You are in no position to claim things like "Black holes don't exist" when you clearly don't even understand the life cycles of stars.

If you had phrased your strong statement as a question, I would have attempted to be more diplomatic. Instead, you made the statement that "Black holes don't exist", and I proved that it was wrong. And somehow this offends you.

I was pointing out that you are wrong and that you needed to study more. If you have a problem with that, then you should do your homework before making such outrageous claims, and you probably shouldn't be in science. The onus is not on me to make sure that you feel that your minority opinion is well-represented...if your theory is attacked, you should defend it. If you cannot do so, then your idea is worthless. Everybody doesn't have an equal say---science doesn't work like this. Some opinions are a priori more valid than others, because some people have studied the problem more than some other people. I'll leave it to you to decide which category your work should be placed in.

bla bla bla ....you made the statement that "Black holes don't exist", and I proved that it was wrong. And somehow this offends you.... bla bla bla

I was gona put on ignore but u r a weakling.

U wana fight ?

Asking others to reading is nothing near proving, Mr. Dumbo.

Singularity, He made a very comprehensible statement using scientific knowledge and just plain good observation skills. Your comeback just being a blatant insult only strengthens his reasoning in my opinion. Personally I believe black holes exist but I do not rule out the possibility that they might not. You on the other hand have already closed your mind and become dead set on something with little scientific proof. Much of science remains to be definitivley explained and closing your mind like that can only lead to your ruin.

It has to do with the binding energy holding the nucleus together. Uranium and other radioactive elements produce energy by fission IOW, they go from heavy Elements to lighter elements, while fusion goes from lighter to heavier. Again, Iron( Iron 56 to be precise) is the at the bottom of this energy ladder. Once you get there you can no longer produce energy by fission or fusion.

By this point, the pressure is so great that it actually pushes the electrons and protons ito each other forming neutrons, the core losses all elememtal properties and just becomes a mass of neutrons. Even if uranium could be produced, the intense pressure would prevent it from undergoing Fission.

I agree. But If there are so many neutrons then they should help in nuclear fission reaction.

The reason i am asking all this is due to simple fact.

http://antwrp.gsfc.nasa.gov/apod/image/0209/hoag_hst.jpg

The central object of this galaxy is so powerful that it has displaced the stars forming a ring just by breeze of its radiation; Thats fantastic amounts of energy released. The object is of vast size but the stars are so close to eachother that a BlackHole must form at the center and once that happens the rest of the stars should take no time to be engulfed by the exponentially growing BH in the center.

But has that happened here ?

It seems that there is no BH, the stars form explode in SuperNovae and are reborn, this will continue until most of the mass is converted in to radiation.

If u all still think what I say has no weight then i challenge u all to show me a single good Ring Galaxy picture or Galaxy with a hole that has no central shining region.

I agree. But If there are so many neutrons then they should help in nuclear fission reaction.
No. Nuclear fission takes place when a large nucleus breaks apart into two pieces. This can be induced by the absorption of a slow moving neutron (if the neutron is too energetic, it will not be absorbed and will not induce fission in the nucleus). Part of ther debris of the fission of the Nucleus will be neutrons. If these neutrons induce fission in other nuclei, then you can get a nuclear explosion. The problem is that only certain isotopes will sustain this reaction. Uranium 235 will, but Uranium 238 won't, for instance. ( since U-235 makes up only a small fraction of any sample of uranium, one has to "enrich the Uranium in order to use it for a reactor or nuclear explosive, IOW, you have to artifically increase the percentage of U-235). The energy released is due to the fact that the by-products of fission have lower binding energies than the original nuclei.

The compressed core of a sun under these conditions cannot undergo fission. There are no individual nuclei to break apart, only a single mass of neutrons. The major player is no longer binding energy, but the gravitational attraction of the mass. There simply is no source of energy available capable of pushing the neutrons apart against their own mutual gravitational attraction. The neutrons cannot even undergo neutron decay (decaying into a positron and electron), becuase the pressure that forced them together in the first place prevents it.


The reason i am asking all this is due to simple fact.

http://antwrp.gsfc.nasa.gov/apod/image/0209/hoag_hst.jpg

The central object of this galaxy is so powerful that it has displaced the stars forming a ring just by breeze of its radiation; Thats fantastic amounts of energy released. The object is of vast size but the stars are so close to eachother that a BlackHole must form at the center and once that happens the rest of the stars should take no time to be engulfed by the exponentially growing BH in the center.

But has that happened here ?

1. How do you know that the stars are so close that a black hole must form? Do you know the average spacing between the stars in this central region and their masses? did you compare the size of the central area to the radius of a black whole of equal mass. Or did you just look at the picture and say to yourself, "Gee, they look awfully close together, they must have formed a black hole"?

2. Formation of blackholes do not result in an increase of gravity. They just compress the source of gravity into a smaller area. If I were sitting just outside a volume of stars that then colapsed into a black hole, I would not detect any change in gravitational attraction. If I was in orbit around that central mass of stars, I would remain in the same orbit around the black hole just as nothing had happened. I would not be pulled into the blackhole.

If there is a blackhole at the center of a galaxy, this does not mean that it will not be surrounded by a cluster of stars that shield it from view.

Singularity, He made a very comprehensible statement using scientific knowledge and just plain good observation skills. Your comeback just being a blatant insult only strengthens his reasoning in my opinion. Personally I believe black holes exist but I do not rule out the possibility that they might not. You on the other hand have already closed your mind and become dead set on something with little scientific proof. Much of science remains to be definitivley explained and closing your mind like that can only lead to your ruin.Yes.. Singularity usually is either intentionally trying to disrupt / hi-jack a thread OR just too ignorant to usefully contribute to the subject. (I tend to believe the first alternative.) BenTheMan has not been here long enough to recognize this consistent pattern. He is quite intelligent and well informed. He will, I predict, soon learn to just ignore such posts.

Janus58 is extremely well informed in the astronomical field, but not active here for weeks at a time (I think). - Perhaps he has not yet had many interactions with singularity.

BenTheMan has not been here long enough to recognize this consistent pattern. He is quite intelligent and well informed. He will, I predict, soon learn to just ignore such posts.

Yes, I may in time learn to ignore the people who claim that black holes don't exist, that evolution is wrong, that the earth is flat, and that GR has some fundamental flaw. I found it interesting that singularity met my criticisms of his idea with a challenge to fight---this reflects on the intellectual content of his posting, I think. That and the repeated use of 'u' which makes the whole thing feel like lunch at middle school as opposed to some sort of intellectual conversation.

If u all still think what I say has no weight then i challenge u all to show me a single good Ring Galaxy picture or Galaxy with a hole that has no central shining region.

This showcases ur ignorance. Galaxies are three dimensional. If u look at a galaxy, u have to look through light years worth of stars. The only way u can hope to determine if a black hole exists in the core of a galaxy is to look at the xray spectrum of the galaxy. Because u are aparently incapable of preforming a simple Google search, I will do it for u.

http://chandra.harvard.edu/photo/2001/xtej1118/
http://chandra.harvard.edu/photo/2001/0204flare/index.html
http://chandra.harvard.edu/photo/2000/0204/index.html

Einstein's equations are perfectly happy with black holes---they are just singular at the origin. This is completely expected, as GR is a classical theory and is expected to break down anyway at very small distances.
Yet a central singularity isn't predicted by Newtonian mechanics, a classical theory.

Yet a central singularity isn't predicted by Newtonian mechanics, a classical theory.

Sure it is. The Newtonian gravitational potential of a point charge is \frac{G M}{r}, and this expression is clearly singular at the origin. Now while I'm not saying the structure of the Newtonian singularity is anything like the singularity in GR, both theories have a singularity. We take this singularity in Newtonian gravity about as seriously as we take the point charge singularities in classical electromagnetism, which is not very seriously.

After reading the first post, I am convinced that black holes indeed exist.

Sure it is. The Newtonian gravitational potential of a point charge is \frac{G M}{r}, and this expression is clearly singular at the origin.
That's a stretch. Newtonian mechanics may allow a central singularity, but unlike GR it doesn't predict that one must form under certain circumstances (namely, when M becomes > r/2). In Newtonian mechanics nothing requires that a singularity forms, and there's ample reason to believe that one cannot exist, since the tidal force is infinite there. Whereas in GR singularities must be taken seriously if black holes are taken seriously.

A classical theory can preclude a singularity simply by invoking a postulate. There is nothing about a classical theory per se that requires a prediction of a singularity. Neither singularities nor black holes need be "expected" (to use Ben's word) in a classical theory.

Newtonian mechanics may allow a central singularity, but unlike GR it doesn't predict that one must form under certain circumstances

The circumstances are that you have a point mass. Do you need other circumstances?

And GR is a classical theory. One can derive Newton's equations from GR, I'm pretty sure. (Wikipedia confirms this.) I think it also goes the other way too---one can derive GR from Newton's equations. I may be wrong about this, though.

http://people.hofstra.edu/faculty/Stefan_Waner/diff_geom/Sec14.html

Classically a singularity forms---but we know Einstein's equations break down as r --> 0. It probably is true that in the full theory of quantum gravity no singularity actually forms---I know string approaches that solve the information paradox using this idea. Classically, at least, the formation of a black hole is evident, both from a mathematical point of view and an observational point of view.

That's a stretch. Newtonian mechanics may allow a central singularity, but unlike GR it doesn't predict that one must form under certain circumstances (namely, when M becomes > r/2). In Newtonian mechanics nothing requires that a singularity forms, and there's ample reason to believe that one cannot exist, since the tidal force is infinite there. Whereas in GR singularities must be taken seriously if black holes are taken seriously.

I actually don't feel that it is a stretch. Systems governed by classical Newtonian gravity are very prone to collapse. For starters, the potential energy of such a system is unbounded from below i.e. dust can always lower its energy by clumping up. Thermal gravitational systems also have a negative capacity in some sense. These facts are routinely manifest in many astrophysical applications, but as we expect (since evidently everything doesn't collapse) the collapse is often arrested by the inclusion of additional physics. Electron degeneracy in white dwarfs, neutron degeneracy in neutron stars, fusion in the Sun, etc. In fact, as this list makes clear, the physics which saves us is often quantum mechanical in nature.

I don't want to make any serious effort to compare the pathologies of various theories, but its safe to say the pure Newtonian gravity isn't exactly generically well behaved.

Furthermore, your assertion that black holes can't be taken seriously if we don't take singularities seriously is totally unsubstantiated. As I have repeatedly and continuously states, the event horizon is a perfectly well behaved surface in spacetime. Nothing particularly crazy is happening there, so the theory is not giving us any obvious reason to doubt it. This is really quite unlike the situation at the singularity where infinities are an obvious sign of trouble.

Ben, it is not really possibly to derive GR from Newton, however, there are several heuristic approaches that allow one to more or less guess the answer.

This showcases ur ignorance. Galaxies are three dimensional. If u look at a galaxy, u have to look through light years worth of stars. The only way u can hope to determine if a black hole exists in the core of a galaxy is to look at the xray spectrum of the galaxy. Because u are aparently incapable of preforming a simple Google search, I will do it for u.

http://chandra.harvard.edu/photo/2001/xtej1118
http://chandra.harvard.edu/photo/2001/0204flare/index.htm
http://chandra.harvard.edu/photo/2000/0204/index.html


Thanks for the proof that the x-rays are a result of SuperNovae activities and not BlackHoles.

"This gas glows in X-ray light because it has been heated to a temperature of millions of degrees by shock waves produced by supernova explosions and perhaps by colliding winds from young massive stars."

http://chandra.harvard.edu/photo/2000/0204/0204_xray.jpg

I actually don't feel that it is a stretch. Systems governed by classical Newtonian gravity are very prone to collapse.
But not prone to collapse all the way to a singularity. There's no maximum escape velocity in Newtonian mechanics. In the annals of physics you'll not find serious mention of a collapse to a singularity predicted by Newtonian mechanics.

I don't want to make any serious effort to compare the pathologies of various theories, but its safe to say the pure Newtonian gravity isn't exactly generically well behaved.
I even agree that Newtonian mechanics is invalid. But that's beside the point here. The point here is that a classical theory (whether valid or not) need not predict black holes and their singularities.

Furthermore, your assertion that black holes can't be taken seriously if we don't take singularities seriously is totally unsubstantiated. As I have repeatedly and continuously states, the event horizon is a perfectly well behaved surface in spacetime. Nothing particularly crazy is happening there, so the theory is not giving us any obvious reason to doubt it. This is really quite unlike the situation at the singularity where infinities are an obvious sign of trouble.
My point is true regardless what happens at a horizon. A singularity is a component of all black holes predicted by GR. Then taking black holes seriously is the same as taking singularities seriously. GR plays nice at a horizon, but a horizon always indicates a prediction of infinities below it.

[QUOTE]Ben, it is not really possibly to derive GR from Newton, however, there are several heuristic approaches that allow one to more or less guess the answer.[/QUOTE'

Fair enough. I thought I had seen it done once.

Maybe you'd better quote the whole thing, instead of misrepresenting the image:

Chandra X-ray image of the innermost 10 light years at the center of our galaxy. The image has been smoothed to bring out the X-ray emission from an extended cloud of hot gas surrounding the supermassive black-hole candidate Sagittarius A* (larger white dot at the very center of the image- a little to the left and above the smallest white dot). This gas glows in X-ray light because it has been heated to a temperature of millions of degrees by shock waves produced by supernova explosions and perhaps by colliding winds from young massive stars.

No. Nuclear fission takes place when a large nucleus breaks apart into two pieces. This can be induced by the absorption of a slow moving neutron (if the neutron is too energetic, it will not be absorbed and will not induce fission in the nucleus).

Why are there no slow moving neutrons in the collapse ?

Now there are two things,

1) if the Iron does reach the stage of Uranium then there was a lot of fusion hence lot of energy to explode the star.

2) the fact that there are so many neutrons that theres high possibility of fission. After all the neutrons are not going anywhere but in the core.

So in all the chances of nuclear explosion is very high, but I am sure i am wrong. I hope that Bill T and BeTheMan can answer such questions instead just critisizing. Any ways those critics have not uttered a word about that magnificent central objects sustained life span.



Part of ther debris of the fission of the Nucleus will be neutrons. If these neutrons induce fission in other nuclei, then you can get a nuclear explosion. The problem is that only certain isotopes will sustain this reaction. Uranium 235 will, but Uranium 238 won't, for instance. ( since U-235 makes up only a small fraction of any sample of uranium, one has to "enrich the Uranium in order to use it for a reactor or nuclear explosive, IOW, you have to artifically increase the percentage of U-235). The energy released is due to the fact that the by-products of fission have lower binding energies than the original nuclei.

But but but, Uranium 238 will form after Uranium 235. Hence ....


The compressed core of a sun under these conditions cannot undergo fission. There are no individual nuclei to break apart, only a single mass of neutrons. The major player is no longer binding energy, but the gravitational attraction of the mass. There simply is no source of energy available capable of pushing the neutrons apart against their own mutual gravitational attraction. The neutrons cannot even undergo neutron decay (decaying into a positron and electron), becuase the pressure that forced them together in the first place prevents it.

What happened to the enormous energy that is released on breakdown of atomic bonds ? I mean where did it go or can it be just overcome by G (G is a weak force of them all).


1. How do you know that the stars are so close that a black hole must form? Do you know the average spacing between the stars in this central region and their masses? did you compare the size of the central area to the radius of a black whole of equal mass. Or did you just look at the picture and say to yourself, "Gee, they look awfully close together, they must have formed a black hole"?

Sorry but thats how i did it. The troubles that theres no galaxy with a hole punched in its center.

As the stars are eaten up the BH becomes more powerful; since its already been circled by the stars (which means it can pull them) its pulling power is growing as it eats more stars, so the already circling star will fall in it as they cant sustain the previous orbits of free fall.

So i concluded that its not a BH thats in action but its a swarm or merging and exploding stars, kinda 3 or 6 star system taken on steroids of billion of star system.



2. Formation of blackholes do not result in an increase of gravity. They just compress the source of gravity into a smaller area. If I were sitting just outside a volume of stars that then colapsed into a black hole, I would not detect any change in gravitational attraction. If I was in orbit around that central mass of stars, I would remain in the same orbit around the black hole just as nothing had happened. I would not be pulled into the blackhole.

If there is a blackhole at the center of a galaxy, this does not mean that it will not be surrounded by a cluster of stars that shield it from view.

I have already told this above.

Maybe you'd better quote the whole thing, instead of misrepresenting the image:

Chandra X-ray image of the innermost 10 light years at the center of our galaxy. The image has been smoothed to bring out the X-ray emission from an extended cloud of hot gas surrounding the supermassive black-hole candidate Sagittarius A* (larger white dot at the very center of the image- a little to the left and above the smallest white dot). This gas glows in X-ray light because it has been heated to a temperature of millions of degrees by shock waves produced by supernova explosions and perhaps by colliding winds from young massive stars.

I think i got confused. May be there are saying that the X-Ray are scattered by the hot Gases and BH is behind the gas clouds.

What do have to say about X-Ray Stars ? Or u want to ignore them as i ignore your supposed to be BH evidence.

http://chandra.harvard.edu/photo/2004/sgra/

Read the above link, these people are themselves confused about what is observed. May be things are not adding up in their equations.;)

You are confusing the issue. No one doubts that point like xray sources are black holes. I quote from the article:

"Thanks to Chandra's unique resolving power, astronomers have now been able to identify thousands of point-like X-ray sources due to neutron stars, black holes, white dwarfs, foreground stars, and background galaxies. "

What the people don't understand is some of the other features of the xray spectra that they see.

The xrays that come from black holes are predicted to have a very specific form by theory. There are no other theories which make this prediction. The astronomers observe these xrays. Thus we are led to believe that black holes exist.

That's a stretch. Newtonian mechanics may allow a central singularity, but unlike GR it doesn't predict that one must form under certain circumstances (namely, when M becomes > r/2). In Newtonian mechanics nothing requires that a singularity forms, and there's ample reason to believe that one cannot exist, since the tidal force is infinite there. ....The only way classical theory can avoid a singularity for a high mass density is to predict / claim that the compressibility (pressure required to make density increase more) goes to infinity with density more rapidly than 1/r^2, (or 1/r ?), but too lazy to be sure of fuctional form as you surely get my point.

But not prone to collapse all the way to a singularity. There's no maximum escape velocity in Newtonian mechanics. In the annals of physics you'll not find serious mention of a collapse to a singularity predicted by Newtonian mechanics.

A generic system of dust (i.e. something with only gravity) in Newtonian gravity will collapse to a singularity. I'm not saying every single system imaginable will, or that every bit of the system collapses (maybe matter is thrown off or something), but quite generally there will be unrestrained collapse. And as in the examples I gave above, this collapse must be arrested by other physics.


I even agree that Newtonian mechanics is invalid. But that's beside the point here. The point here is that a classical theory (whether valid or not) need not predict black holes and their singularities.

Who cares what the generic classical theory says. We have two good theories of gravity, both predict collapse, and we don't take the singularities in either one seriously.


My point is true regardless what happens at a horizon. A singularity is a component of all black holes predicted by GR. Then taking black holes seriously is the same as taking singularities seriously. GR plays nice at a horizon, but a horizon always indicates a prediction of infinities below it.

I think its silly to suggest that we must take the singularity seriously if we take the horizon seriously. Perhaps an analogy will help. The equations of fluid dynamics can accommodate singularities for example in the form of sinks and vortices. Do you seriously think we can't take any of the flow seriously just because some part of it is singular?

Why are there no slow moving neutrons in the collapse ?

The nuclei are all crammed together is a single mass. There is no room for isolated neutrons

Now there are two things,

1) if the Iron does reach the stage of Uranium then there was a lot of fusion hence lot of energy to explode the star.
No, It takes energy to fuse elements from Iron on up. That energy would come from the star, removing energy that is being use to help support from collapsing. Using that energy to fuse Iron up to Uranium would cause the star to shrink.

2) the fact that there are so many neutrons that theres high possibility of fission. After all the neutrons are not going anywhere but in the core.
Wrong. It takes more than just an abundance of neturons for fission to occur, it takes nuclei that are prone to fission. There are a lot of neutron abundant heavy elements, but only a small fraction of their isotopes are fissile.


So in all the chances of nuclear explosion is very high, but I am sure i am wrong.
You are, but even if enough Uranium could be formed to generate such a reaction, the energy output would be lmuch less than the energy it took to form the Uranium in the first place. It wouldn't even swell the star back up to the size it was before it gave the energy needed to fuse the Uranium.



But but but, Uranium 238 will form after Uranium 235. Hence ....

Will it? Nucleosynthesis is a complicated process, and just because U-238 is a heavier isotope than U-235, doesn't mean that it is formed after U-235 or even that you pass through U-235 on the way to it;




What happened to the enormous energy that is released on breakdown of atomic bonds ? I mean where did it go or can it be just overcome by G (G is a weak force of them all).

The energy is still there stored in the bonds between the neutrons. Only upon releasing the compression due to gravity would it be released.



Sorry but thats how i did it. The troubles that theres no galaxy with a hole punched in its center.

There's no reason to expect to see one. The black hole is hidden by the halo of stars and dust surounding it.

As the stars are eaten up the BH becomes more powerful; since its already been circled by the stars (which means it can pull them) its pulling power is growing as it eats more stars, so the already circling star will fall in it as they cant sustain the previous orbits of free fall.

I've already explained that this is not the case. Even if closer-in stars were to fall into the black hole, stars further out would not be affected. While the mass and gravity of the Black hole itself would increase, the gravitational force on these stars will not. because, the mass of those closer-in stars were already contributing to the force of gravity experienced by these further-out stars already. Moving them inward further and merging them with the black hole does not increase their gravitational influence on stars further away. .

Janus58,
I've already explained that this is not the case. Even if closer-in stars were to fall into the black hole,
Hope you don't mind me asking a few questions that I am not clear as to the answer. First, about how large is the accretian disk for a supermassive black hole such as SagA*? Is it large enough to contain several stars at one time, at different distances from the event horizon? What would cause the stars orbiting within the accretian disk to 'fall into' the black hole rather than continually orbiting the black hole like planets orbiting a sun? As the black hole consumes the dust etc. orbiting nearer the event horizon than the star, the total gravitational attraction exerted upon the star shouldn't change, should it? I understand the dust can loose momentum through collisions and such, but what causes the 'streams' of material flowing from an expanding red giant star to the accretian disk as is shown in animations? Wouldn't the material orbit faster and faster as it neared the black hole, smearing out any appearance of a 'stream' of matter as shown in the earlier animations and appear as a large, dilute, accretion disk between the two bodies instead?
While the mass and gravity of the Black hole itself would increase, the gravitational force on these stars will not. because, the mass of those closer-in stars were already contributing to the force of gravity experienced by these further-out stars already. Moving them inward further and merging them with the black hole does not increase their gravitational influence on stars further away. .
Again, this seems as if the black hole would not 'suck' anything into it, other than gas and dust that looses angular momentum through collisions while orbiting inside the accretion disk, or (2) if the mass falling into the black hole already had motion (momentum) in the direction of the black hole.
Next, the animations I have seen that were based upon actual observation of SagA* over a period of time show stars that are in very eliptical orbits, speeding up as they near the black hole and slowing as they move farther away, similar to comets orbiting our sun. Even for stars that approach the black hole through prior motion in that direction, shouldn't most just be captured in elipital orbits instead of falling in?

I think as the BH grows, the orbit of the stars circling it should come near it each time it gets heavier and thus the center of the Ring Galaxie should collapse, but it doesnt. Hence there is no BlackHole, YAAAHOOOOO hip hip hurrraay

BTW, dont u think this thread deserves a note,
Transference Gravity Effect (http://sciforums.com/showthread.php?p=1310976#post1310976)

I think as the BH grows, the orbit of the stars circling it should come near it each time it gets heavier and thus the center of the Ring Galaxie should collapse, but it doesnt.

Do you have any idea how large the center of that galxy is?

Singularity,
I think as the BH grows, the orbit of the stars circling it should come near it each time it gets heavier and thus the center of the Ring Galaxie should collapse, but it doesnt. Hence there is no BlackHole, YAAAHOOOOO hip hip hurrraay
You seem to assume there are many stars in circular (round) orbits near the black hole. Binary star systems are quite common, but they formed that way, from condensing gas and dust. A stellar-mass black hole with a companion was what was illustrated in your animation, not supermassive black holes as found in galatic centers. Many of the stars in orbit around the supermassive black hole at the center of at our own galaxy, at least, are observed to be in elliptical orbits. Perhaps the ring galaxy had a great number such stars in elliptical orbits. Two galaxies, each with supermassive black holes, could have merged sometime in the distant past. The central black holes may have merged slightly off-center with respect to the orbiting stars in the resulting galaxy. As the black hole gained mass and the event horizon increased in diameter, the stars with those elliptical orbits could be given a 'gravity boost' while near the event horizon, making the orbit more and more elliptical until they were eventually ejected out of the the black hole's gravitational grasp. Perhaps those ejected stars could then be slowed and captured by the gravitational mass of all those stars in the outter part of the galaxy, adding to their numbers and forming the 'ring'? In other words, the 'inner' stars were eventually given a gravitational boost and ejected to the outside of the galaxy. Just a thought.

Singularity,

You seem to assume there are many stars in circular (round) orbits near the black hole. Binary star systems are quite common, but they formed that way, from condensing gas and dust. A stellar-mass black hole with a companion was what was illustrated in your animation, not supermassive black holes as found in galatic centers. Many of the stars in orbit around the supermassive black hole at the center of at our own galaxy, at least, are observed to be in elliptical orbits. Perhaps the ring galaxy had a great number such stars in elliptical orbits. Two galaxies, each with supermassive black holes, could have merged sometime in the distant past. The central black holes may have merged slightly off-center with respect to the orbiting stars in the resulting galaxy. As the black hole gained mass and the event horizon increased in diameter, the stars with those elliptical orbits could be given a 'gravity boost' while near the event horizon, making the orbit more and more elliptical until they were eventually ejected out of the the black hole's gravitational grasp. Perhaps those ejected stars could then be slowed and captured by the gravitational mass of all those stars in the outter part of the galaxy, adding to their numbers and forming the 'ring'? In other words, the 'inner' stars were eventually given a gravitational boost and ejected to the outside of the galaxy. Just a thought.

I think when we talk about growing BlackHoles we should assume that

"What goes around comes around"

or elliptical to your suggestion ;)

Do you have any idea how large the center of that galxy is?

Cant u see the luminous difference between the center and the ring ?

Cant u notice the difference in density of stars between the center and the ring ?


Well, then look again, http://antwrp.gsfc.nasa.gov/apod/image/0209/hoag_hst.jpg


And now talk about its size and u will realize that this center is about to implode, but it doesn't. Ohuu boy there are just fantastic number of stars for not to do criss crossing, colliding and merging.

A generic system of dust (i.e. something with only gravity) in Newtonian gravity will collapse to a singularity. I'm not saying every single system imaginable will, or that every bit of the system collapses (maybe matter is thrown off or something), but quite generally there will be unrestrained collapse. And as in the examples I gave above, this collapse must be arrested by other physics.
Newtonian mechanics is subject to other known physics that presumably always arrests a collapse to a singularity. Whereas GR’s prediction of a collapse to a singularity trumps all known physics.

Who cares what the generic classical theory says. We have two good theories of gravity, both predict collapse, and we don't take the singularities in either one seriously.
I did an extensive search of Newtonian mechanics in connection with a singularity. I can’t find any article that relates the two. I see no mention of a prediction of collapse to a singularity by Newtonian mechanics. I think singularities in GR are implicitly taken seriously when black holes, which contain a singularity according to the theory, are taken seriously. Taking black holes but not singularities seriously is simply a case of trying to have it both ways.

I think its silly to suggest that we must take the singularity seriously if we take the horizon seriously. Perhaps an analogy will help. The equations of fluid dynamics can accommodate singularities for example in the form of sinks and vortices. Do you seriously think we can't take any of the flow seriously just because some part of it is singular?
I’m not familiar with fluid dynamics, but it sounds like you’re merging something allowed with something predicted to actually occur under some circumstances. I would say that Newtonian mechanics does not even allow r=0, since that is an infinite tidal force. Whereas GR predicts that an infinite tidal force must occur under some circumstances. GR predicts its own demise in that way, whereas Newtonian mechanics does not (and I’m not suggesting that Newtonian mechanics is thereby valid).

The only way classical theory can avoid a singularity for a high mass density is to predict / claim that the compressibility (pressure required to make density increase more) goes to infinity with density more rapidly than 1/r^2, (or 1/r ?), but too lazy to be sure of fuctional form as you surely get my point.
I think something like that (something that prevents a singularity) is assumable when the alternative is the tidal force becoming infinite. Newtonian mechanics does not deny such an assumption (which can explain why no serious mention of a collapse to a singularity predicted by Newtonian mechanics can be found). Whereas GR does deny such an assumption. According to GR, nothing can prevent a collapse to a singularity under certain circumstances.

Cant u see the luminous difference between the center and the ring ?

Cant u notice the difference in density of stars between the center and the ring ?

If I thought that u were older than 16, I would ask you if you had ever seen an oncoming car at night. If it is far away, the two headlights look like one because the optics in your eye prohibits you from resolving the lights as individual emitters. As the car approaches, you can gradually see that the distance is large, perhaps a meter.

All of this to say that just because it looks like one big star doesn't mean it actually is. These things are thousands or millions of light years away. There is no doubt that the stars in the center of this galaxy are denser, but there is no reason to believe that the center of the galaxy is one big star. The distance between our sun and the next closes star is 4 light years. In the Milky way, the average star distance is several light years. So even if this decreases by a factor of ten in the center of the galaxy, the average interstellar distance is 6 light months. This means the average distance between stars would be something like 32000 times the average Earth Sun distance, yet somehow, after 4 billion years, the Earth hasn't fallen into the sun.

So why would you think that two stars, which are much farther apart, would fall towards each other?

I think singularities in GR are implicitly taken seriously when black holes, which contain a singularity according to the theory, are taken seriously.

Maybe this is what you are confused about. The fact that a singularity appears at r = 0 means that GR breaks down in this limit. This is not news, and had been known for a long time, and no one expects that GR describes the universe at r=0. When we say that black holes contain singularities (they should contain Singularity--forgive the pun) we mean that the classical theory is singular. This doesn't invalidate any of GR's other predictions, this doesn't mean that all of gR should be thrown out, this just means that quantum gravity is a hard problem. This is just a reaffirmation of what we already knew---GR is a classical theory.

Physics Monkey told you in another thread that GR is defined in terms of a smooth Euclidean manifold. When the manifold ceases to be smooth (i.e. the space ceases to be a manifold), you can no longer define a good tangent space on which to do calculations, and you can no longer have a good set of coordinates, (I could go on)...this is the point where GR can be said to fail.

Again, we have known that this is the case since Feynman tried to quantize gravity using the mehtods he developed to deal with photons and electrons.

Second, the appearance of a horizon (an horizon?) just says that there exists a mass who has an escape velocity larger than the speed of light. This was calculated before GR was even contmeplated in like 1780 by a guy named John Michell. (Wikipedia tells me that Laplace did the same calculation in 1796.)

We believe that stars collapse, and because the calculations tell us that they can form black holes undercertain conditions, and that the same calculations give fantastic predictions which have been measured, we believe them. We also believe in black holes because there is not reason not to. They are not consistent at r=0, but this is not shocking, because as you pointed out, we can't even believe GR at r=0. That's why we study Euclidean Quantum Gravity, a la Hawking, or Loop Quantum Gravity, a la Lee Smolin, or string theory, a la everyone else in the world.

GR is not inconsistent, it just doesn't apply at r = 0. When physicists say "a singularity exists at the center of the black hole" they mean "If we extrapolate Einstein's equations past their range of applicability, it appears that a singularity forms."

Taking black holes but not singularities seriously is simply a case of trying to have it both ways.

The black hole surely forms, (or, if you like, a horizon surely forms) as we can do experiments to check for them. We have predictions and experimental verificaitons. As much as you would like to believe Singularity, black holes do exist. From the quantum view, everytihng about a black hole is defined on its horizon---it's temperature, its entropy, etc. No quantum numbers, or no information if you like, is carried anywhere BUT the horizon. In GR, (i.e. classicaly) you can never retrieve information from the inside of a black hole, so you'll never know what happens there.

And likePhysics Monkey said, many other theories give infinities. This just means we can't trust them in certian limits. Feynman's theory of QED (which I mentioned earlier) gives nonsensical answers for very large momenta. This just means we can't trust the results in such a regime. But experimentally this theory has been confirmed to something like 13 decimal places, or one part in ten trillion. It is by far the most accurate theory ever developed by man.

So I am loathe to admit that yes, you are right. GR is inconsistent, but only inasmuch as everybody studying the problem for the last fifty years has already known.

If I thought that u were older than 16, I would ask you ...
That's ironic. Why not try to set a good example yourself?

Maybe this is what you are confused about. The fact that a singularity appears at r = 0 means that GR breaks down in this limit. This is not news, and had been known for a long time, and no one expects that GR describes the universe at r=0. When we say that black holes contain singularities (they should contain Singularity--forgive the pun) we mean that the classical theory is singular. This doesn't invalidate any of GR's other predictions, this doesn't mean that all of gR should be thrown out, this just means that quantum gravity is a hard problem. This is just a reaffirmation of what we already knew---GR is a classical theory.
My point is that a classical theory of gravity need not predict black holes or singularities. Your comments here don’t refute that. There is no guarantee that a new theory of quantum gravity will save GR. The problem that arises from GR’s prediction of a collapse to a singularity could just as well be caused by GR being an invalid theory of gravity everywhere, even in weak gravity; i.e. GR could approximate the correct theory of gravity wherever it’s been experimentally tested.

Second, the appearance of a horizon (an horizon?) just says that there exists a mass who has an escape velocity larger than the speed of light. This was calculated before GR was even contmeplated in like 1780 by a guy named John Michell. (Wikipedia tells me that Laplace did the same calculation in 1796.)
In Newtonian mechanics a “black hole” does not necessarily contain a singularity (and it can be assumed that there is no singularity, since that means an infinite tidal force). In that theory, unlike in GR, an object launched from the horizon can rise above the horizon. In Newtonian mechanics, unlike in GR, there is no maximum escape velocity.

GR is not inconsistent, it just doesn't apply at r = 0. When physicists say "a singularity exists at the center of the black hole" they mean "If we extrapolate Einstein's equations past their range of applicability, it appears that a singularity forms."
Defining a “range of applicability” for GR is the method by which astronomers and physicists have it both ways. A more logical interpretation is to assume that GR’s prediction that singularities must form in certain cases means that it is not the correct theory of gravity anywhere, and hence the prediction of black holes, because they contain a singularity, should be held as suspect.

The black hole surely forms, (or, if you like, a horizon surely forms) as we can do experiments to check for them. We have predictions and experimental verificaitons.
We have predictions. We have no experimental confirmation. The “confirmation” to date assumes that GR is the correct theory of gravity. There is no direct observational evidence of a black hole. There is only indirect evidence that assumes that GR is the correct theory of gravity. The strongest-gravity experimental confirmation of GR is in relatively extremely weak gravity at an r-coordinate over 200,000M (geometric units). That’s one hundred thousand times the r-coordinate 2M where a horizon is predicted to exist.

As much as you would like to believe Singularity, black holes do exist.
You cannot support this statement with experimental evidence. None exists.

And likePhysics Monkey said, many other theories give infinities. This just means we can't trust them in certian limits. Feynman's theory of QED (which I mentioned earlier) gives nonsensical answers for very large momenta. This just means we can't trust the results in such a regime. But experimentally this theory has been confirmed to something like 13 decimal places, or one part in ten trillion. It is by far the most accurate theory ever developed by man.
GR predicts that a singularity must form if a black hole forms. GR contradicts QED at a singularity. Then GR’s prediction of a black hole is tantamount to a contradiction with QED.

So I am loathe to admit that yes, you are right. GR is inconsistent, but only inasmuch as everybody studying the problem for the last fifty years has already known.
Regardless how long it’s been known, it’s a serious issue. The severity of the issue doesn’t diminish with time. But more to my point, GR’s prediction of black holes and singularities in no way indicates that all classical theories of gravity must follow suit.

Zanket I am sorry but you are just wrong. GR is a classical theory. As all classical theories, it doesn't apply when you talk about quantum effects. Put another way, it does not survive in the limit as r --> 0. This is well established, and no one debates this.

Defining a “range of applicability” for GR is the method by which astronomers and physicists have it both ways.

But this is exactly how we do physics. The point is that GR makes predictions which are useful---gravitaitonal radiation (Nobel Proze 1993 I think), eratic orbit of Mercury. Every time you use a GPS device, the GPS takes GR effects into account so that it can accurately tell you where you are. So in this sense, GR is not only right, but you may be using it every day you drive to work. We have no quantum theory of gravity, so of course it won't work in certain regimes.

You cannot support this statement with experimental evidence. None exists.

Then you are at odds with most people who study the problem. The ultra short gamma ray bursts have no other explanation. No other physics is known that will explain them. The fact that there are supermassive black holes at the centers of galaxies explains both why there are huge amounts of exrays coming out of that region of the sky, and the orbits of the innermost stars. Further, every attempt at doing quantum gravity gives us horizons---this is a fact. Hawking does it with Euclidean path integrals, Lee Smolin does it with spin networks, and everybody else does it with strings.

GR predicts that a singularity must form if a black hole forms. GR contradicts QED at a singularity. Then GR’s prediction of a black hole is tantamount to a contradiction with QED.

I don't think you understood my point. QED is not well behaved at very high energies. This tells us that there is new physics. QED has a "range of applicability", as you put it, and new physics has to come in before QED fails. The analogy with GR is that classically, at least, a singularity forms. This is bad behavior. Thus we expect new physics to come in and take over before a singularity forms. But the prediction of black holes remains, because GR (as you have pointed out) still holds across the horizon.

Regardless how long it’s been known, it’s a serious issue. The severity of the issue doesn’t diminish with time.

Then go fund your local string theorist.

This is the point---every theory we right down is an effective theory. The standard model is an effective theory. GR is an effective theory. Electromagnetism is an effective theory. Saying that GR is inconsistent is the same as saying the electromagnetism is inconsistent. Yet your TV still works. Your computer still works---all built on 150 years of understanding an inconsistent theory?

That's ironic. Why not try to set a good example yourself?

According to the forum rules here (http://www.sciforums.com/showthread.php?t=42924), this is an unacceptable post. The rules exist to keep the forum scientific.

Zanket I am sorry but you are just wrong. GR is a classical theory. As all classical theories, it doesn't apply when you talk about quantum effects. Put another way, it does not survive in the limit as r --> 0. This is well established, and no one debates this.
That’s beside the point. It doesn’t prove that every classical theory of gravity must predict black holes and their singularities. It doesn’t prove that Newtonian mechanics predicts a collapse to a singularity.

But this is exactly how we do physics. The point is that GR makes predictions which are useful---gravitaitonal radiation (Nobel Proze 1993 I think), eratic orbit of Mercury. Every time you use a GPS device, the GPS takes GR effects into account so that it can accurately tell you where you are. So in this sense, GR is not only right, but you may be using it every day you drive to work. We have no quantum theory of gravity, so of course it won't work in certain regimes.
Pointing out that GR is experimentally confirmed in weak gravity neither proves that GR is the correct theory of gravity, nor proves that every classical theory of gravity must predict black holes and their singularities.

Then you are at odds with most people who study the problem. The ultra short gamma ray bursts have no other explanation. No other physics is known that will explain them. The fact that there are supermassive black holes at the centers of galaxies explains both why there are huge amounts of exrays coming out of that region of the sky, and the orbits of the innermost stars. Further, every attempt at doing quantum gravity gives us horizons---this is a fact. Hawking does it with Euclidean path integrals, Lee Smolin does it with spin networks, and everybody else does it with strings.
Nothing here proves that GR is the correct theory of gravity. Another theory of gravity may explain these observations and be just as experimentally confirmed as GR is. Short gamma ray bursts are just circumstantial evidence, not experimental confirmation. They do not have no possible other explanation. They could be explained by another theory of gravity that predicts gravitational time dilation and gravitational length contraction to any degree (just like GR does above a horizon), but does not predict black holes. Such a theory could predict short gamma ray bursts but predict far different results in the same area than GR does for, say, relativistic orbital precession.

I don't think you understood my point. QED is not well behaved at very high energies. This tells us that there is new physics. QED has a "range of applicability", as you put it, and new physics has to come in before QED fails. The analogy with GR is that classically, at least, a singularity forms. This is bad behavior. Thus we expect new physics to come in and take over before a singularity forms. But the prediction of black holes remains, because GR (as you have pointed out) still holds across the horizon.
New physics could just as easily come in before the horizon forms. I say that GR plays well across a horizon only because this thread isn’t the place to discuss its provable self-inconsistency at the horizon.

This is the point---every theory we right down is an effective theory. The standard model is an effective theory. GR is an effective theory. Electromagnetism is an effective theory. Saying that GR is inconsistent is the same as saying the electromagnetism is inconsistent. Yet your TV still works. Your computer still works---all built on 150 years of understanding an inconsistent theory?
If GR was self-inconsistent only at a horizon, its self-consistency elsewhere wouldn’t at all help a case made for the existence of black holes.

According to the forum rules here (http://www.sciforums.com/showthread.php?t=42924), this is an unacceptable post. The rules exist to keep the forum scientific.
It’s not rude to point out your rudeness and request that you stop.

The nuclei are all crammed together is a single mass. There is no room for isolated neutrons No, It takes energy to fuse elements from Iron on up. That energy would come from the star, removing energy that is being use to help support from collapsing. Using that energy to fuse Iron up to Uranium would cause the star to shrink.
Wrong. It takes more than just an abundance of neturons for fission to occur, it takes nuclei that are prone to fission. There are a lot of neutron abundant heavy elements, but only a small fraction of their isotopes are fissile. ...[/i].

Clearly I am no match to say anything on what u said, sorry its out of my reach.

That’s beside the point. It doesn’t prove that every classical theory of gravity must predict black holes and their singularities. It doesn’t prove that Newtonian mechanics predicts a collapse to a singularity.

I don't know that there's a proof of this---my guess is that you haven't constructed one, because it would probably involve math, which you have avoided at every junction at all costs. What I do know is that science currently contains no other explanation for some of the observed phenomena. What I do know is that if GR is proven wrong, then any new theory which replaces it must be mathematically identical to GR in the weak field approximation. This will let us know that it is correct.

Nothing here proves that GR is the correct theory of gravity.

There is no need to prove this---one only need look at the experimental results. "The correct theory" and "the theory that gives the right answers" are pretty much the same.

New physics could just as easily come in before the horizon forms.

Then it would be drastically different than what people are working on today. All three major theories of quantum gravity contain horizons, and they only apply when gravity becomes strong. The problem is that GR is consistent in the weak field approximation---here it reduces to Newtonian Gravity (and if you argue that Newtonian gravity doesn't work then you are just a lunatic). The horizon of a large black hole, for example, is perfectly happy with a weak gravitational field (flat space)---i.e. if there were some new dynamics, it would have to come from the causal structure of space-time, not the structure of space-time itself. That is, you want a new theory of gravity which relies on causality, and you will probably lose the formulation of space-time as an Euclidean manifold.

If GR was self-inconsistent only at a horizon, its self-consistency elsewhere wouldn’t at all help a case made for the existence of black holes.

You are consistently missing my point---GR is perfectly consistent across the horizon, despit what you think. GR is inconsistent at r = 0, but that's something we've known for a long time. The case made for black holes is an experimental one.

So here's the challenge. Explain the gamma ray bursts with a new theory of gravity and I will take you seriously.

It’s not rude to point out your rudeness and request that you stop.

I never said that you were rude---I am not as easily offended as you are. I simply pointed to the fact that the scientific content of this post was especially lacking. And if you think I am rude, think about how you treat people who claim that global warming is wrong, or that AIDS isn't caused by HIV, or that Intelligent Design should be taught in schools, or that the Holocaust never happened. From a scientific standpoint, your conclusions hold the same weight as theirs. (I know, of course, that you are a liberal---I know that you probably hold strong opinions on these subjects, which is why I used them as an example.) You are claiming that scientific concensus is wrong, and I have even seen you use some of the same language as these people. My sarcasm is interpretted as rudeness, and somehow I am a bad person because I know more than you do.

I don't know that there's a proof of this---my guess is that you haven't constructed one, because it would probably involve math, which you have avoided at every junction at all costs.
The burden of proof is on you, not me, to defend your statement that black holes and their singularities are expected by a classical theory.

What I do know is that science currently contains no other explanation for some of the observed phenomena.
Or it does but it’s not recognized. Either way, it doesn’t prove that GR is correct. It doesn’t prove that all classical theories of gravity predict black holes and their singularities.

What I do know is that if GR is proven wrong, then any new theory which replaces it must be mathematically identical to GR in the weak field approximation. This will let us know that it is correct.
Any new theory must agree with experimental results within the margin of error, that's all.

There is no need to prove this---one only need look at the experimental results. "The correct theory" and "the theory that gives the right answers" are pretty much the same.
So you think it’s okay to barely test a theory and declare it correct? Show me some experimental confirmation of GR where the r-coordinate r is less than 200,000M (geometric units). A theorized horizon is at r = 2M.

Then it would be drastically different than what people are working on today. All three major theories of quantum gravity contain horizons, and they only apply when gravity becomes strong.
That means nothing. There’s no experimental confirmation of any form of quantum gravity.

That is, you want a new theory of gravity which relies on causality, and you will probably lose the formulation of space-time as an Euclidean manifold.
You’re just speculating.

You are consistently missing my point---GR is perfectly consistent across the horizon, despit what you think.
It is proven to be self-inconsistent at a horizon in another thread here.

The case made for black holes is an experimental one.
And a circumstantial one. All “confirmation” of black holes to date assumes as a basis that GR is the correct theory of gravity. There is no experimental confirmation of GR anywhere near a theorized horizon.

So here's the challenge. Explain the gamma ray bursts with a new theory of gravity and I will take you seriously.
That’s a red herring. There’s no burden on me to give a new theory to show that GR need not be the correct theory. The burden of proof is on you to show otherwise; you’re the one making the claim to the contrary.

I simply pointed to the fact that the scientific content of this post was especially lacking.
No, you did more than that. You were rude.

And if you think I am rude, think about how you treat people who claim that global warming is wrong, or that AIDS isn't caused by HIV, or that Intelligent Design should be taught in schools, or that the Holocaust never happened. From a scientific standpoint, your conclusions hold the same weight as theirs.
Yes, about their conclusions.

You are claiming that scientific concensus is wrong, and I have even seen you use some of the same language as these people.
It’s okay to claim that scientific consensus is wrong. I don’t attack people in Physics & Math; that’s against the rules.

... because I know more than you do.
When will you prove it?

Ok Zanket. This will be my last post in the thread. I will not claim to have won, because I have not convinced you of anything. Singularity has aparently conceded the debate to me, so I can take solace in that.

I will respond to a few points above, but will sumarize my objections to your arguments quickly. (Feel free to have the last word here, but I do not think it will change anything.) My problem with all of your work is that you are using layman's definitions of "locality" and "reference frame". You reference frames are not local, no matter what definition you dig up from Wikipedia or Taylor and Wheeler. If you define reference frames to be arbitrarily large you are sure to find fault with GR, because you are starting from a faulty premise. Also, talking about contradictions is one thing, but you should actually take the time to calculate things if you are to convince physicists. At the end of the day, only a calculation will prove your case. Physics Monkey and myself have both pointed out cases where the physical system seems to be finite, yet singularities occur. Both him (her?) and I can back up these statements with calculations. Your argument relies on inconsistent definitions, and is backed up with no calculations---either one of which should be enough to demonstrate that it is, at best, speculative, and at worst completely wrong.

You will say, I'm sure, that such thought experiments are good enough to damn the whole theory, but this is simply not true. The fact is that GR has tremendous predictive power, and is experimentally confirmed. I have talked with some cosmologists about this, and they have assured me that the experimental tests of GR do not rely on the fact that GR is correct. I will trust their words over yours, for the fact that they have studied this problem with sufficient rigor.

The burden of proof is on you, not me, to defend your statement that black holes and their singularities are expected by a classical theory.

I know of no proof that black holes are a generic feature of a classical theory of gravity, however, GR is the best classical theory of gravity that we have (one can derive Newtonian gravity from GR), and it contains several solutions with horizons. (One may point to other classical theories of gravity, like Brans Dicke theory http://en.wikipedia.org/wiki/Brans-Dicke, but there black holes are also predicted. I cannot comment on other classical theories of gravity.) The appearance of a singularity in the classical theory does not invalidate GR, it only tells you that it doesn't work at r = 0. That's ok, because we have expected that all along.

Any new theory must agree with experimental results within the margin of error, that's all.

I disagree with this. In the weak field approximation, any new theory of gravity must obey Einstein's equations, and so must be interpretable in this limit as space-time curvature. The interpretation of gravity as space-time curvature should probably be a generic feature of the underlying theory, but I could be convinced otherwise by someone who has studied the problem. If you are keeping track, this is speculative, but you have offered no rebuttals of this speculation.

You’re just speculating.

Again, maybe. But the logic is as follows. You want a theory of gravity in which new physics comes in before the formation of a black hole. If there is no physical principle or symmetry which specifically prevents this from happening, it must be due to the causality and not the curvature. In other words, we know GR breaks down at large curvature. We also know that the curvature across a black hole's horizon is negligible. So GR is expected to hold across the horizon of a black hole---which one COULD take in a weak field approximation, which we have already argued agrees with experiments. The only thing different about a horizon is that the causal structure of space-time is different. So any new theory of gravity should take the causal structure of space as fundamental, and not the curvature of space-time.

It is proven to be self-inconsistent at a horizon in another thread here.

This is why I added the caveat "despite what you think". I have pointed out why you think GR is inconsistent above. You will never be convinced that you are wrong because you will only accept definitions which prove your point.

All “confirmation” of black holes to date assumes as a basis that GR is the correct theory of gravity. There is no experimental confirmation of GR anywhere near a theorized horizon.

Are you familiar with the experiments? Rapidly spinning black holes emit radiation along their poles preferrentially. The way I remember the calculation (preformed by Sir Martin Rees), the intensity of this radiation is proportional to the spin and the mass of the collapsing object. It is a statistical mechanical argument and not a GR argument. See this paper, for example : http://arxiv.org/PS_cache/astro-ph/pdf/9301/9301007.pdf. There is no observation of a horizon, this is true, but this is likely never to come. So in your mind, nothing will ever be proved.

No, you did more than that. You were rude.

Awww well Im awful sorry.

“ And if you think I am rude, think about how you treat people who claim that global warming is wrong, or that AIDS isn't caused by HIV, or that Intelligent Design should be taught in schools, or that the Holocaust never happened. From a scientific standpoint, your conclusions hold the same weight as theirs. ”
Yes, about their conclusions.

Just as long as you acknowledge this. When it comes to GR, I would say that there is more of a consensus than in the case of global warming. I want to make this perfectly clear to anyone keeping up with this discussion. Go talk to MattMarr about how the Illuminati have fooled us all in to believing that GR is correct and that the Earth is really flat. Your conclusions hold the same weight.

It’s okay to claim that scientific consensus is wrong. I don’t attack people in Physics & Math; that’s against the rules.

I'm glad to see that you are the beacon of morality which illuminates SciForums. If by "attack someone" you maen "prove them wrong with experimental evidence and sound science", then I say that the rules are wrong and I will never follow them. If your arguments are crap then they are crap. That's the end of the story.

Anyway, by this point you have no doubt been sufficiently offended by me, which has really been my goal all along. For posterity's sake, I have sumarized my main objections to your comments above, and hopefully you will do the same before preaching to me about being offensive or something. Whatever. Hopefully a thinking person will be able to follow my objections to both your and singularity's arguments, and see the glaring flaws in both lines of logic.

I dont care a damn to waste time on man made non existing things like Reference Frame Bullshit.

Although I have not carefully read all of the Zanet/BenTheMan exchange, sometimes a little too heated, I think they agree more than they disagree.

Both seem to recognized that both GR can Newtonian gravity can form such dense aggregates of mater that light can not escape - I.e. agree that "event horizons" are real.

Zanet is strongly of the opinion that singularities do not in fact exist. I think Ben also believes this may be the case as GR is not a reliable theory as r --> 0. I also (and Zanet agreed) suggested that the pressure required to prevent the collapse to a singularity (even in the classical gravity case) must got to infinity (more rapidly than 1/r or 1/r^2 - still to lazy to work out which).

I do not understand the great conflict except perhaps as being caused by "black hole" sometimes carrying the idea of it being a singularity. Really as Ben noted, we can know nothing about what is going on inside the EH, so how can it matter?

PS to Singularity You are slipping - that post 63 out-of-left field attempt to hi-jack a thread is not up to your normal standards.

Good post Billy, it seems that they were just debating the specifics, when essentially they believe the same concepts.

I am curious however to your thoughts about what happens when matter becomes dense enough for a black hole. Do you believe it crushes down to a singularity or is there a point (other than a singularity) where matter cannot be crushed any further?

Good post Billy, it seems that they were just debating the specifics, when essentially they believe the same concepts.

I am curious however to your thoughts about what happens when matter becomes dense enough for a black hole. Do you believe it crushes down to a singularity or is there a point (other than a singularity) where matter cannot be crushed any further?I do not like to think singularities are real, so my bet is that just as the neutrons prevent further collapse in a neutron star, something will keep the finally singularity from happening.

I go even farther and suggest that if you try to pack quarks into a package much denser than the protons and neutrons (not sure that density is a valid concept on the nuclear scale - but you get my idea, I'm sure) that some rapid resistance to further volume reduction will be part of the quark to quark interaction. I seem to recall some discussion of a "quark star" but forget what was said.

Maybe I should clarify then I promise I'll shut up.

Good post Billy, it seems that they were just debating the specifics, when essentially they believe the same concepts.

Well.... Zanket deosn't believe in GR, as per this:
http://zanket.home.att.net/

We have argued at length about these things in another thread. Zanket believes he has found a thought experiment which shows that horizons are inconsistent with GR, not just singularities. I think that he is working from faulty definitions.

While I agree that the classical theory is inconsistent at r-->0, zanket believes that the classical theory is inconsistent at the horizon. This is a huge difference, basically because of this (sorry if I quote myself):

You want a theory of gravity in which new physics comes in before the formation of a black hole. If there is no physical principle or symmetry which specifically prevents this from happening, it must be due to the causality and not the curvature. In other words, we know GR breaks down at large curvature. We also know that the curvature across a black hole's horizon is negligible. So GR is expected to hold across the horizon of a black hole---which one COULD take in a weak field approximation, which we have already argued agrees with experiments. The only thing different about a horizon is that the causal structure of space-time is different. So any new theory of gravity should take the causal structure of space as fundamental, and not the curvature of space-time.

This is something which is drastically different from any physics that has been invented, accept for possibly Zanket's theory.

Ok I'll go now before Singularity rebuffs me again.

I think that the collapse causes the explosion. The core gets heavier and closer together as it cools then it collapses when it reaches the tipping point. The matter that follows it in is heated by gravitational compression, and if you get a really good collapse, that heat is a significant fraction of what you would get if the mass were converted completely to energy. It is contained for a time then it explodes.

....Zanket believes he has found a thought experiment which shows that horizons are inconsistent with GR, not just singularities. ... zanket believes that the classical theory is inconsistent at the horizon. This is a huge difference,...I agree that is huge! I missed that in my quick skim - It is hard to believe he really thinks that a classical gravity field can not be so strong that the escape velocity is greater than c. So, if zanket is reading, I ask him to comment or give post number where he explains why. I seem to recall from my skim of your exchange, that he specifically said the opposite - namely that there is no upper bound on the escape velocity in classical gravity (and I think that is correct.)

As not even light can travel faster than c, this implies that there is a horizon.

Yes.

I recall a gay bar in LA catering to Blacks named The Black Hole. I thought I saw Count Sudoku inside!:eek:

...
PS to Singularity You are slipping - that post 63 out-of-left field attempt to hi-jack a thread is not up to your normal standards.

Sure Mr. Smarty, now try ansrin this :

Do u really believe in BH singularity ? And if u do then by the Distorted definition of Singularity and not the real Singularity definition. Can Singularity sustain Gravitons and hence gravity itself ?

I think that the collapse causes the explosion. The core gets heavier and closer together as it cools then it collapses when it reaches the tipping point. The matter that follows it in is heated by gravitational compression, and if you get a really good collapse, that heat is a significant fraction of what you would get if the mass were converted completely to energy. It is contained for a time then it explodes.

Finally theres one human who can see.

...
What could you possibly be debating? And what do gravitons have to do with anything? They have not been discovered yet. Are you depending on them for some kind of support of your own "theories"?

The matter is collapsed to zero size yet its capable of generating gravity, how incredible, let alone talking how Gravity escapes this singularity.

Sure Mr. Smarty, now try ansrin this :

Do u really believe in BH singularity ? ...[/B]Usually I just ignore you, but answer to this was post 66. Do you not read posts? But only pick threads at random to throw off-thread comments into?

Re black holes: time dilation is infinite at the event horizon. This means no collapsing star has finishing collapsing yet, and never will. It means there are no singularities. Any discussion of singularities is in the reference frame of the falling object, and is taking place "beyond the end of time" in a kind of theoretical never-never land.

Re the principle of equivalence: it isn't valid. Yes, it got Einstein started, but there's no vital tidal gradient in the accelerating frame. It really isn't equivalent to gravity. Zanket is right, but it doesn't mean GR is invalid, so he's wrong too. I like this quote from J L Synge:

"The Principle of Equivalence performed the essential office of midwife at the birth of general relativity, but, as Einstein remarked, the infant would never have gone beyond its long clothes had it not been for Minkowski’s concept [of space-time geometry]. I suggest that the midwife be buried with appropriate honours and the facts of absolute space-time faced".

Usually I just ignore you, but answer to this was post 66. Do you not read posts? But only pick threads at random to throw off-thread comments into?

May b its due 2 ur arrogant attitude

About post 66; u are struck at the collapse , your collapse doesnt result into a supernova though all the energy elements for the nova are present there.

if black holes don't exist, than how come it has been proven that something out there blocks out light of nearby stars...and that something is there for a long time.

Also if black holes didn't exist than how come it has been also sighted how a black hole consumes a nearby star and that star is engulfed into the hole?

if you want evidence/facts on my side (because you dont believe what I just said) than tell me and I will find you the articles on this.

if black holes don't exist, than how come it has been proven that something out there blocks out light of nearby stars...and that something is there for a long time. I know there are lot of dead cold stars out there. http://www.pitt.edu/~cejones/GeoImages/0PlanetaryFormation/GalaxyDust/SombreroGalaxy.jpg


Also if black holes didn't exist than how come it has been also sighted how a black hole consumes a nearby star and that star is engulfed into the hole? Thats not true, black hole formation doesnt mean the stars gravity increase or something, its just that the companion star expands and collides with a cold star.

I am waiting for an event, where a Red giant merges with a cold star and becomes a blue star, there are lot of binaries out there which means there will be such an even in case of cold with a red giant.


if you want evidence/facts on my side (because you dont believe what I just said) than tell me and I will find you the articles on this.

Waiting for christmas ?

Waiting for christmas ?

don't be rude. this sort of thing takes a long time to find, I am just asking if it is needed.

Singularity: there are stars out there. Some don't shine any more. They're black, they're small, with intense gravity. And if you fall into one you can't get out, no way, no how. So they're holes. Hence they're black holes. Now my understanding of physics tells me there's no central singularity, but they're still black holes, and whilst I've never seen one, I do believe they exist.

Singularity: there are stars out there. Some don't shine any more. They're black, they're small, with intense gravity. And if you fall into one you can't get out, no way, no how. So they're holes. Hence they're black holes. Now my understanding of physics tells me there's no central singularity, but they're still black holes, and whilst I've never seen one, I do believe they exist.

http://images.astronet.ru/pubd/2004/10/09/0001199934/m15_xcomp.preview.jpg

XTE J1118+480

is an actual black hole consuming nearby stars on its Path

http://www.astronet.ru/db/xware/msg/1170921

http://images.astronet.ru/pubd/2004/10/09/0001199934/m15_xcomp.preview.jpg

XTE J1118+480

is an actual black hole consuming nearby stars on its Path

http://www.astronet.ru/db/xware/msg/1170921

"Black hole candidate XTE J1118+480 ..."

I say its a cold star candidate.

I say its a cold star candidate.

If your trying to disprove something generally held as true to exist, you might want to use something better than conjecture to prove your point.:rolleyes:

If your trying to disprove something generally held as true to exist, you might want to use something better than conjecture to prove your point.:rolleyes:

instead why dont u tell me how u know for sure that those objects are blackHoles and not cold stars. Since u already know that u should be able to tell it, or else it becomes blind faith.

instead why dont u tell me how u know for sure that those objects are blackHoles and not cold stars. Since u already know that u should be able to tell it, or else it becomes blind faith.

they are not seen in visible in light and emit x-rays only.

... Blind faith?

....
Matter falling on a surface and emitting radiation has a well-known and specific spectral signature. 138 suspected neutron stars were examined against 100 or so (I forget exactly how many) suspected black holes. Ther results were that 138 neutron stars showed this characteristic spectral signature, and 100 or so black hole candidates did not. Fairly conclusive.

First thing is that u people are ignorant about the X-Ray stars.

Second, is there any article on Matter crashing on to a cold star ?

I wonder how many dead stars are out there since they died last 5 to 13 billion years ago. :bawl:

So? They do not have the gravitational potential, as normal or even degerate matter, to cause the observed effects on the surrounding stars and material.

Now what?

Thats what i am trying to tell u all. The dead stars are too many out there , dont ignore them, they should form a major chunk of the universe, since universe is too old not to have them in vast numbers.

My problem with all of your work is that you are using layman's definitions of "locality" and "reference frame". You reference frames are not local, no matter what definition you dig up from Wikipedia or Taylor and Wheeler. If you define reference frames to be arbitrarily large you are sure to find fault with GR, because you are starting from a faulty premise.
Wrong thread. And not my definitions; they’re Einstein’s, Taylor’s, Thorne’s, and Wheeler’s definitions. Even Einstein disagrees with you about the size of an inertial frame. Take it up with them.

At the end of the day, only a calculation will prove your case.
Calculations already done by Taylor, Thorne, and Wheeler. (I used published definitions, and predictions from calculations, done by these relativity experts.) They contradict, as shown in the other thread.

Your argument relies on inconsistent definitions, and is backed up with no calculations---either one of which should be enough to demonstrate that it is, at best, speculative, and at worst completely wrong.
Relies on definitions and calculations by Einstein, Taylor, Thorne, and Wheeler, not me. Take it up with them. Neither you nor anyone else could refute the other thread—it’s that clear cut. (And I notice you didn’t try.) GR is self-inconsistent.

You will say, I'm sure, that such thought experiments are good enough to damn the whole theory, but this is simply not true. The fact is that GR has tremendous predictive power, and is experimentally confirmed.
Barely experimentally confirmed. No experimental confirmation at r-coordinate r < 200,000. “Tremendous” predictive power unconfirmed in all but extremely weak gravity nowhere near a theorized horizon of a black hole. You could not show otherwise. Nor does any amount or precision of experimental confirmation save a self-inconsistent theory.

I have talked with some cosmologists about this, and they have assured me that the experimental tests of GR do not rely on the fact that GR is correct. I will trust their words over yours, for the fact that they have studied this problem with sufficient rigor.
Half truth. There is experimental confirmation of GR in relatively extremely weak gravity. But experimental “confirmation” of black holes depends on the validity of GR; cosmologists use GR to determine the mass, consuming the one and only one observation they use to “confirm” black holes. You could not show otherwise.

I know of no proof that black holes are a generic feature of a classical theory of gravity, ...
Nor could there be one. (A classical theory could even rule out black holes simply via a postulate.) This is mainly what I disagreed with you about in this thread. Now we are in agreement.

The appearance of a singularity in the classical theory does not invalidate GR, it only tells you that it doesn't work at r = 0.
It tells us more than that. It tells us that GR predicts its own demise, by predicting that a body must collapse to r = 0 under certain conditions.

I disagree with this. In the weak field approximation, any new theory of gravity must obey Einstein's equations, ...
The meanings of the words approximation and obey contradict here. A new theory need only approximate Einstein’s equation’s predictions where GR has been experimentally confirmed (relatively extremely weak gravity), just like GR needed only approximate Newton’s equation’s predictions in weaker fields. I notice you limit your comment to weak fields, when a black hole’s field is extremely strong—I thought you said GR was experimentally confirmed for black holes. :)

The interpretation of gravity as space-time curvature should probably be a generic feature of the underlying theory, but I could be convinced otherwise by someone who has studied the problem. If you are keeping track, this is speculative, but you have offered no rebuttals of this speculation.
No rebuttal is needed. Spacetime curvature is synonymous with tidal force. A tidal force is experimentally confirmed.

Again, maybe. But the logic is as follows. You want a theory of gravity in which new physics comes in before the formation of a black hole. If there is no physical principle or symmetry which specifically prevents this from happening, it must be due to the causality and not the curvature. In other words, we know GR breaks down at large curvature. We also know that the curvature across a black hole's horizon is negligible. So GR is expected to hold across the horizon of a black hole---which one COULD take in a weak field approximation, which we have already argued agrees with experiments. The only thing different about a horizon is that the causal structure of space-time is different. So any new theory of gravity should take the causal structure of space as fundamental, and not the curvature of space-time.
A “theory of gravity in which new physics comes in before the formation of a black hole” could be had simply by fixing GR’s proven self-inconsistency at a horizon.

I have pointed out why you think GR is inconsistent above. You will never be convinced that you are wrong because you will only accept definitions which prove your point.
I won’t be convinced I’m wrong unless I’m refuted. Which neither you nor anyone else has done. All of the definitions, and predictions of GR from calculations, are those of top relativity experts, including Einstein. All I did was show that they prove a self-inconsistency of GR.

Are you familiar with the experiments? Rapidly spinning black holes emit radiation along their poles preferrentially. The way I remember the calculation (preformed by Sir Martin Rees), the intensity of this radiation is proportional to the spin and the mass of the collapsing object. It is a statistical mechanical argument and not a GR argument. See this paper, for example : http://arxiv.org/PS_cache/astro-ph/pdf/9301/9301007.pdf. There is no observation of a horizon, this is true, but this is likely never to come. So in your mind, nothing will ever be proved.
Yes, of course, if there’s no experimental confirmation of a black hole, then they are not shown to exist in Nature. That’s not a flaw of my thinking; that’s the scientific method. No amount of calculations (which is all that PDF contains) confirm that Nature works like the calculations predict. Only experimental observations do. That is how physics works. Physics does not tell Nature what to do. Nature tells physicists whether their theories are valid.

Astronomers need not observe a horizon directly. Horizons could be all but experimentally confirmed if there was experimental confirmation of another type of GR’s predictions near a horizon, like relativistic orbital precession. But no such experimental confirmation exists today. The observations near a theorized horizon that are used to “confirm” black holes today are plugged into GR to get the mass, so they don’t experimentally confirm GR at all. All that can be said about these observations is that if GR is the correct theory of gravity, then a black hole should exist below the region of the observation.

Awww well Im awful sorry.
Heartfelt I’m sure. The rules are designed to keep threads on-topic and scientific.

When it comes to GR, I would say that there is more of a consensus than in the case of global warming. …
No consensus overrules the lack of experimental confirmation of black holes, or of any other prediction of GR in that territory. Physicists can believe whatever they want; science doesn’t bow to their beliefs. There’s a huge difference between a consensus based on mountains of data (global warming) and consensus based on no data (black holes). One is science, the other is religion.

I liked the candor of this comment by an astronomy writer in Black Holes by Pickover: “The biggest unsolved problem [related to black holes] is whether there are any black holes in the universe. In my opinion, the evidence so far is slim, and even black-hole aficionados admit this fact (when they believe the public/taxpayers aren’t listening).”

… I want to make this perfectly clear to anyone keeping up with this discussion. Go talk to MattMarr about how the Illuminati have fooled us all in to believing that GR is correct and that the Earth is really flat. Your conclusions hold the same weight.
Unlike black hole believers, I actually have information upon which my conclusions are based. And that information comes straight from Einstein, Taylor, Thorne, and Wheeler.

I'm glad to see that you are the beacon of morality which illuminates SciForums. If by "attack someone" you maen "prove them wrong with experimental evidence and sound science", then I say that the rules are wrong and I will never follow them.
That is not what “attack someone” means. It means a personal attack. Attacking their ideas is A-okay and expected here.

If your arguments are crap then they are crap.
You should show they are crap, not just claim it. For example, give one shred of experimental confirmation of black holes, or of any other prediction of GR in that territory. Or go to the other thread and show a problem with it—a bona fide problem, not just some consensus based on no data. You can’t do it. You have given neither experimental evidence