Talk:Black hole

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Observer at the origin

Has there been any analysis done placing the observer at the center of a mass accumulating sphere? At some critical time (mass, density), the observer would see the the event horizon disappear(?) and the volume within expand? Like a big bang? —Preceding unsigned comment added by Pereza (talk • contribs) 21:34, 21 January 2008 (UTC)

Vandalism

I got into an edit conflict with 80.39.98.175, who was trying to vandalize this talk page. If this page is vandalized again, please undo it, as I couldn't do that properly due to the edit conflict.DragonOfLegend (talk) 10:23, 16 January 2008 (UTC)DragonOfLegend

The article is vandalized. When I was logged out, I noticed that the page begins with the line saying something about black holes being created from people. But when I logged in, I couldn't see that line. Will someone please fix this? I myself can't do it.

When I was logged in and checking in on this page, I did not see that. But when I was not logged in and went to this page, forgetting to log in, I saw the comment and immediately logged in, and returned to the page. Needless to say, it did not appear, not when I viewed the page OR tried to edit the page. I don't know WHAT glitch or whatever-thing that causes this, but someone best refer this to an admin or something if it doesn't clear up in the next week or so. IceUnshattered (talk) 00:33, 17 January 2008 (UTC)

I found the same thing - the statement appears if you are not logged in and does not appear if you are logged in. It also does not appear in the edit page. Very odd.PhySusie (talk) 01:03, 17 January 2008 (UTC)

I posted it to the help page and they fixed it - really, really fast! So it's fine now. PhySusie (talk) 16:30, 17 January 2008 (UTC)

I saw it today and it was there, i actually registered to fix it but when i was in it wasnt there no more! andron2000 22, January 2008 —Preceding comment was added at 03:48, 23 January 2008 (UTC)

Magnetic Field

How does something which emits nothing and devours everything have a magnetic field?

Can someone post this topic in the article.

Actual picture of a black hole

I heard talk that a couple days ago "they" took an actual picture of a black hole. Can someone link to it if it's true?

-G 02:32, August 27, 2007 (UTC)

There is this photo from 1995 from Hubble of what appears to be a black hole.

http://hubblesite.org/gallery/album/galaxy_collection/pr1995049g/

It would be great if someone uploaded it and added it to the article - there's not enough actual photos in this article. It's from the hubble telescope, so should be fine to add to wikicommons.

JohnFlux (talk) 00:04, 29 November 2007 (UTC)

One cannot take an ordinary picture of a black hole. Is it and infared or other spectrum picture or is it of a black hole's jets?

murdock_cb 16 January 2008 - I read news today that the Chandra X-Ray Observatory took some really cool pictures of some black hole. It would be cool if someone uploaded those onto here. —Preceding unsigned comment added by 138.237.89.67 (talk) 21:21, 16 January 2008 (UTC)

Sizes of Black Holes

The Black Hole article states that "High-energy particle accelerators such as the Large Hadron Collider (LHC), if certain non-standard assumptions are correct (typically, an assumption of large extra dimensions). However, any black holes produced in such a manner will evaporate practically instantaneously, thus posing no danger to Earth." However, the LHC article indicates that the "claim has been disputed; the existence of Hawking radiation has not been experimentally observed." The Black Hole article here implies that the theory of Hawking Radiation is an undeniable truth when clearly the opposite is true, it has not been observed or proven. Then the BH article goes on to contradict itself, "Hawking radiation is a theoretical process by which black holes can evaporate into nothing. As there is no experimental evidence to corroborate it and there are still some major questions about the theoretical basis of the process, there is still debate about whether Hawking radiation can enable black holes to evaporate." I recommend that the BH article, where indicated in Size of Black Holes, be changed to reflect the fact that if micro black holes were formed they may or may not evaporate instantaneously, or the information about micro black holes forming on earth be eliminated entirely since the information relative to Earth is extraneous to the section. Skjaybe 08:34, 10 August 2007 (UTC)

I recommend simply changing to article to reflect the fact that micro black holes are thought to be unstable because of Hawking Radiation, rather than asserting they ARE unstable. Jpowell 14:14, 10 August 2007 (UTC)

My new recommendation is that the article should be changed simply because Hawking Radiation is a theory and nothing anyone one earth has observed can confirm or deny its existence. 76.178.168.28 08:11, 14 August 2007 (UTC)

I don't think it's relevant that Hawking Radiation hasn't been observed, it should be mentioned, it simply shouldn't be stated as fact. Jpowell 19:48, 14 August 2007 (UTC)

Black Hole Collision

Is it possible for two black holes to collide (similar to galaxies colliding)? If that can happen, what would result?

Sure. you just get a bigger BH (and a whole bunch of gravitational waves, presumably). --Oscar Bravo 08:29, 8 August 2007 (UTC)

When two black holes coalesce, the area of the resulting event horizon is greater than the sum of the areas of the event horizons of the original black holes. This is stated in the Hawking area theorem. —The preceding unsigned comment was added by Jono87 (talk • contribs) 09:36, August 23, 2007 (UTC).

Another question, how do black holes maintain energy equilibrium. The singularity eats up any body crossing event horizon, how much of the matter is absorbed IN the black hole? If any matter is absorbed in the black hole, does its mass increase and if it does increase does it generate a paradox, that, the singularity being formed in the first place was because of infinitesimally small volume of an object? If the singularity is to stay, the additional(if any) mass must also vanish somewhere. Please treat this question as a speculation or a wild thought.

As matter falls into a BH, the BH's mass increases accordingly. Imagine you have BH of a given mass and are orbiting it at a safe distance (so the tidal forces are not too great) then your orbital period is a simple function of that mass of the BH. If you then chuck a lump of matter into the BH, it's mass will increase and your orbital period will decrease (ie, you will speed up). As regards the singularity, you seem to think things vanish when they hit it. They don't. All that happens is that the matter is compressed to a point of zero volume (hence infinite density). So the mass of the singularity increases although its volume stays zero. All matter that falls into a BH ends up in the singularity so, in fact, all BHs of any mass have the same "size" - zero! The event horizon is just an imaginary shell around the BH that limits what we can see happening and its size depends on the mass of the singularity. --Oscar Bravo 08:29, 8 August 2007 (UTC)

Black hole collision as it relates to the Big Bang Theory

When two black holes "side swipe" each other so to speak, in such a way that their event horizons touch, there is a chance that the gravity of each will negate the gravity of the other. This would cause a space between the black holes were gravity was far to weak to keep the containment consistent on the massive amount of matter stored in the hole. Without the infinite pressure pressing down on it, the matter would rupture out in an extremely powerful blast. this blast would be from both of the black holes, and would be of such force and magnitude that it would blow both black holes completely apart. The boundless energy stored within each hole wouldn't of course stop at blowing the black hole apart, it would send a massive wave of destruction ripping through local space, blowing everything in the area away. I propose that this is what caused the big bang. Two super massive black holes came too near, and tore this part of the universe apart billions of years ago. Not beginning the universe, but rather just exploding a comparatively very small part of it.

No hair theorem

I've reinstated the para about the limitations of the "no hair" theorem because: (a) nobody answered my question about why it was deleted; (b) another section refers to it.

If anyone thinks the para about limitations should be deleted, please explain why.Philcha 12:14, 27 June 2007 (UTC)

I think the paragraph should be deleted unless a supporting reference is found. It doesn't make sense to me. Why should the existence of the cosmological constant have any effect on whether we need more than 3 variables to describe a classical black hole?--Michael C. Price ^talk 23:18, 27 June 2007 (UTC)

I got the info from the article on the No hair theorem, which itself is a little short on references. I'll look around for some, but can't promise results in any particular timeframe. At present we have a dilemma: (a) as it stands, the comments in Black Hole and No Hair Theorem are consistent with each other but with no references; (b) if the paragraph in Black Hole is removed, it becomes inconsistent with No Hair Theorem. I prefer option (a) as a temporary expedient - it only fails if the writer of the corresponding part of No Hair Theorem got it seriously wrong. I see that there's been very little recent activity on both the No Hair Theorem article and its Talk page - is that a good sign or a bad one?Philcha 10:19, 28 June 2007 (UTC)

Thanks for highlighting the lack of references over at No hair theorem. I suspect the author got it wrong, but I'll check up before taking any action, but (like you) I can't promise any action soon. I notice that NHT says the NHT fails in the presence of non-abelian Yang Mills -- well, that's the universe we live in! --Michael C. Price ^talk 20:34, 28 June 2007 (UTC)

Actually the author did get it right (there were some caveats in the text I overlooked earlier). I've added some references to the NHT page which demonstrate (I think) that the NHT is basically sound.--Michael C. Price ^talk 21:32, 1 July 2007 (UTC)

Thanks for beefing up No hair theorem, and the point that NHT works with positive cosmological constant. But I'm still puzzled about a couple of things: (a) Your comment above is ambiguous - does our observed universe have non-abelian Yang Mills fields (which disable the NHT)? (b) Superstring theory posits a spacetime with 11 or more dimensions, which would disable the NHT, and AFAIK superstring theory is currently the best bet to reconcile general relativity and quantum mechanics.Philcha 09:32, 10 July 2007 (UTC)

Only some of your points I can answer: (a) the strong and electroweak forces are both examples of non-abelian Yang Mills (EM on its own is an abelian YM); I think what this means is that a black hole can retain some non-abelian YM charges -- but apparently these aren't conserved(?), which why we are not much concerned with them(?). (b) No idea about superstring theory, which was why I added the caveat that the NHT applies to classical (i.e. non-quantised) black holes).--Michael C. Price ^talk 11:19, 10 July 2007 (UTC)

Thanks. I agree that superstring theory may not be relevant because Black hole adopts a strictly classical GR approach except where explicitly noted (that may be a limitation, but we have to give the general reader some breaks). Sounds like there may still be some doubts about whether the existence in our universe of non-abelian Yang Mills make the NHT inapplicable. Can anyone clear this up?Philcha 22:57, 13 July 2007 (UTC)

speculation

This is just speculation but what if black holes are objects moving faster then the speed of light?They have some of the properties to sugest this.There singularity is infinitly massive whitch is what would hapeen if something is moveing faster then the speed of light and if the univeres has a infinate life time the we chould accont black holes as emmerging from some disstant time in the futer lets say 1000⁹⁹⁹⁹⁹⁹ then one chould emerge from nothing traviling faster then the speed of light and travel back in time (since objects moving faster then the speed of light travel back in time).To us it would seem as if they are moving foward in time to support this have we ever seen (indarectly)a black hole form?No we have not.This would also explane hawking radiation because as it traveled back in time it would appear to lose mass.(I know there is many spelling problems and would like you not to say anything about it in your cooments and please dont call me a crackpot.)57th street kid 03:59, 29 June 2007 (UTC)57th street kid

You're a crackpot. --Oscar Bravo 12:02, 29 June 2007 (UTC)

And Wiki is not the place for "speculation". --Michael C. Price ^talk 13:31, 29 June 2007 (UTC)

To defend what i said if the universe dose not end then wouldent quantum uncertency make "impossible" things happen?~~57th street kid~~

Hey guys, give user:57th street kid a break and remember WP:Don't bite the newbies. He / she has read the article and thought about it, and that's a success for Wikipedia. Now I'll attempt to answer the questions.

The singularity is not infinitely massive - in fact mass is one of the few externally measurable properties of black holes (see No hair theorem. In terms of general relativity the singularity has infinite density and infinite surface gravity, but that's because a finite mass has been compressed into zero radius.

Your second question needs an answer from a real physicist, which I am not. But it's a sensible question. Recent astronomical observations indicate that the expansion of the universe (or rather, of space-time) is accelerating. That means the universe will not collapse back on itself in a Big Crunch (reversal of the Big Bang). So in that sense it looks like the lifetime of our universe s infinite. But it will be a very empty universe, totally unlike the way it is now: a finite amount of matter will be spread over an infinite volume; and physicists currently expect that about 20 billion years from now there will be a Big Rip, in which the expansion of space-time causes even sub-atomic particles to disintegrate. So now we have 2 concepts pulling in opposite directions: quantum mechanics suggests that in an infinite time any event which is physically possible can happen; but after the Big Rip even black holes cannot stay in one piece. A good answer to your question requires someone who can work the equations (I can't).

So come on, people, can anyone answer user:57th street kid's question?Philcha 10:06, 10 July 2007 (UTC)

The Big Rip is highly conjectural.--Michael C. Price ^talk 11:12, 10 July 2007 (UTC)

Hey, I have a question for all you physics fans.... A black hole has some insane gravitational pull right, masses accelerate when they are pulled by gravity.... light has mass. How can light not accelrate??? and wheres einstien in all this? Anyways let me know why it cannot please thanks.

Janiston 06:58, 12 July 2007 (UTC)DOrius Light

Good question. When a principle usually works but sometimes doesn't, physicists try to redefine their terms so that it always works. To make "masses accelerate in a gravitational field" work out in the case of light, we had to change the definition of "accelerate" from "velocity changes" to momentum changes". In the case of light falling straight into a black hole (or a pile of mass of any sort), the speed doesn't change but the mass does. A change in mass at constant speed is also a change in momentum and therefore an acceleration. The mass of a photon is proportional to its frequency, so light falling into a black hole is blue-shifted. (Another interesting case is when light does not fall into a massive body but just passes by it. In that case the energy and therefore the magnitude fo the momentum does not change, but the direction does, which also amounts to a change in momentum because momentum is a vector quantity.) --Art Carlson 08:06, 12 July 2007 (UTC)

You mean "energy" of a photon. Photons don't have mass. Jpowell 22:34, 6 August 2007 (UTC)

What's the difference? --Art Carlson 15:47, 8 August 2007 (UTC)

Just to expand on what Carlson said, E=mc^2. Energy is mass, mass is energy. Photons do not have rest mass - which is an important distinction. In literature, because energy and mass are the same thing it has now become accepted that just saying 'mass' means rest mass, because otherwise you'd just say energy. So "Photons don't have mass" is valid, if by mass you mean rest mass. And "Photons have mass" is also valid, if by mass you mean energy. Just to be clear, photons will have a gravitational attraction etc JohnFlux (talk) 06:16, 29 November 2007 (UTC)

I like to think of it this way: Light can definitely accelerate, just not in the way you're used to at the slow speeds matter moves at. Nothing can move past the cosmic speed limit (the speed of light). So, light is stuck at that speed and "accelerates" (increases its kinetic energy) by increasing its frequency (blueshifting), which in a particle sense means it's vibrating faster. And it "slows down" by redshifting. It only appears to move at the same speed from our perspective, but from its perspective, it is definitely responding to gravity. Perhaps a physicist could let me know if my explanation is valid... Richcon 06:54, 21 July 2007 (UTC)

Okay many questions about black holes but the main one that grips me is the view we have of a black hole. If the black hole trully sucks in all the matter around it then it would be a sphere not a 3d disc. Surely all the pictures and readings show a cross section of a black hole and when viewing you would see the energy and radiation resulting from disruption to our side of the hole. Hence you would not see the whole in the black whole or be able to detect a whole. It would look like a circle of high radiation with a weaker but still high energy and very heavy center. Paul amateur philosopher - England.

Are you talking about pictures like this? Ignore those, they're not based on any real physics. Or are you talking about pictures like this? That's supposed to be a picture of an accretion disc, not of the hole itself. The hole itself is presumably supposed to be the black spot in the center; it's an oblate spheroid, not a disc. This picture conflates the two others (meaning it's also wrong, but even more deceptive than the first one). -- BenRG (talk) 18:25, 18 February 2008 (UTC)

What if no gravitation is necessary to explain black holes? A researcher in Massachusetts has slowed light to a dead stop at temperatures approaching absolute zero (article: www.smithsonianmag.com/science-nature/phenom-200801.html) If a patch of space the same temperature as created in his lab were to come between an observer and a star being observed the photons from the star would be frozen in motion and to the earthly observer it would appear as though the star had been swallowed by a black hole but in reality it would be more like a cloud on a partly cloudy day passing over the sun.- Terry —Preceding unsigned comment added by 74.70.206.210 (talk) 04:16, 5 January 2008 (UTC)

Light slows down when it passes through a medium of high refractive index, and that's what these people are making: media of incredibly high refractive index. The fact that it's near absolute zero isn't directly relevant. Light doesn't automatically go slower at lower temperatures. -- BenRG (talk) 18:25, 18 February 2008 (UTC)

Janiston posted a pretty good question. I would think that light could indeed travel quicker while ascending towards the gravitational singularity of a black hole. Many scientists claim that although they're not exactly sure of how quickly one would have to travel to escape the event horizon, but they & we all know it'd have to be faster than the speed light. -[Rayne] 16:00, 7 February 2008 (UTC) —Preceding unsigned comment added by 206.208.93.60 (talk)

You can't sensibly talk about light traveling faster or slower in general relativity because there's no standard of reference for the speed except the speed itself. Null lines are null lines; light travels at the speed of light. I don't know what to say about these "many scientists" except that I don't think they're cosmologists. -- BenRG (talk) 18:25, 18 February 2008 (UTC)

Template sections

User:Monmnom turned several sections of this category into templates. See the following:

Template:Black hole introduction

Template:Sizes of black holes

Template:Major features of rotating black holes

Template:What happens when something falls into a black hole

Template:Formation and evaporation

Template:Techniques for finding black holes

Template:Black hole candidates

Template:History of the black hole concept

The user may also intend to add the following:

Template:What makes it impossible to escape from black holes?

Template:Major features of non-rotating, uncharged black holes

Template:More advanced black hole topics

This looks like a really bad idea. Although I have stated in the past that material should be shifted to subpages to improve the readability of the article, moving all of the text to templates seems like a really lousy idea. This just seems to make the structure of the article very confusing, and it makes it difficult for users to monitor changes to the article. Moreover, it hardwires the section names and makes it difficult to rearrange or reorganize material in the article, which users probably do not want.

I have not seen this done in any other articles. If User:Monmnom wants to do this, he should discuss it here first. Otherwise, I advocate deleting the existing templates. What do other people think? Dr. Submillimeter 22:48, 14 July 2007 (UTC)

I think User:Monmnom is not familiar with the workings of sub-articles and templates. If there is no objection, I will go ahead and delete the templates listed above under 'housekeeping' (CSD:G6). Owen× ☎ 23:02, 14 July 2007 (UTC)

what? —Preceding unsigned comment added by 200.24.98.46 (talk) 20:04, 18 October 2007 (UTC)

What makes it impossible to escape from black holes?

Explanations involving spacetime geometry, event cones, and purely mathematical concepts like "undefined" make my brain implode. I imagine those non-physicists reading Wikipedia would agree. Though these explanations are definitely valid, they are also very arcane. I think there's a much simpler explanation for why objects can't escape a black hole: inside the event horizon the required escape velocity would be greater than the speed of light, which is an impossibility.

I wrote up the following explanation. If nobody objects, I'll work it into that section. Here it is:

An object's escape velocity is determined by the gravitational pull it is trying to escape and its distance from that object. With the example of the Earth, as a spaceship falls closer to the Earth's surface, its necessary escape velocity increases. But there's a limit to how close it can get, the Earth's surface. Beneath the surface, the Earth's gravitational pull starts to drop as it is now pulling in multiple directions and cancelling itself out.

peanut butter and jelly sandwiches!

A black hole is so small and dense that an object could fall practically to its center without "landing" on anything. And as the object falls, the pull of gravity becomes ever stronger. At some point, this results in the velocity required to escape the black hole reaching speeds faster than the speed of light. As General Relativity states that nothing can ever accelerate to faster than the speed of light, escape becomes impossible. The point at which this happens is the black hole's event horizon.

- Richcon 06:11, 21 July 2007 (UTC)

It's very nice, but not correct. The whole escape velocity thingy implies a ballistic object like a cannonball. The trouble is that, in your picture, you could get out of an event horizon by crawling up a rope, or being hoisted up on a space elevator. You can't, and the out-dated escape-velocity explanantion can't explain why not.

The trouble is that a BH is defined precisely in terms of space-time geometry and to understand a BH, you simply must understand space-time geometry. Otherwise, you're trying to explain fire to a dolphin.--Oscar Bravo 13:31, 23 July 2007 (UTC)

Explanations based on escape velocity have some big limitations. (a) They only deal with unpowered objects (e.g. a shell fired from a gun), so can't explain why a very powerful spaceship can't escape (or an elevator, as someone pointed out above). (b) They assume Newton's theory of gravity, which applies to pairs of objects with non-zero mass. So they can't explain why light can't escape (photons have zero rest mass). (c) The definition of escape velocity allows the smaller object to move an indefinite distance from the larger one before falling back, so escape velocity can't explain the existence of an event horizon.

There are books which present general relativity in a fairly non-mathematical way, perhaps you should look for some. Or try searching the Web for "black hole", there are some fairly non-mathematical pages. I say this as a fellow dolphin trying to understand fire.Philcha 00:43, 28 July 2007 (UTC)

Presumed Black Hole?

Tt seems everything has it's deniers these days so I suppose it's no surprise that there exist Black Hole deniers too. It may well be that the points of very high gravity that are observed in the Universe are not the objects predicted by GR, but the overwhelming scientific consensus is that they are BHs. Until compelling evidence is provided to the contrary, it is reasonable to reach the tentative conclusion that BHS are real. This article is about the canonical concept of Black Holes - if you want to debunk them, go write an article entitled "Fringe ideas about why BHs don't exist". --Oscar Bravo 08:13, 23 July 2007 (UTC)

I think that a small portion of the article should be devoted to criticism and fringe theories, maybe a paragraph or two if appropriate. The source that was cited for that passage is sketchy to say the least, but after looking at it, it seems that the contents are already covered in the alternative models section. As long as the space allotted to fringe theories is proportional to how credible they are, I see no problems with including them. --Gimme danger 08:51, 23 July 2007 (UTC)

Exactly - small portion and proportional are the keywords here, methinks... The comments I removed were in the introductory paragraph and so were unduly weighted.--Oscar Bravo 13:23, 23 July 2007 (UTC)

I may be biased on this, but denying black holes is NOT on the fringes of science. The basic stopping point is this: say you have matter collapsing into what should be enough mass to form a singularity. Would a horizon form in finite time? The immediate answer from SR and GR is no, as time dilation would seem to forbid the observation of a horizon from the outside. This problem exists in quantum, classical, and field theory analyses, and AFAIK has not been resolved by any standard physics (I have no clue about string theory).

The second question, posed by the guys at Case, is similar as it asks what happens as matter collapses to the Schwarzschild radius. I can't remember the formalism from Vachaspati's lecture on this, but an enormous amount of mass-energy is radiated away in the collapse, such that the Schwarzschild radius shrinks continuously as the matter collapses.

Both of these analyses forbid the presence of black holes, which is great for the universe because it prevents a hell of a lot of paradoxes, even if it makes things a little less interesting. Note that all of these analyses use multiple well-confirmed theories: GR, QFT, and stat-mech, the latter two of which are the most robust in all of physics.

Having only been to schools sympathetic to this position, I am not aware that these ideas are not widely accepted - if the math is correct, GR people have some work to do. Certainly it's all fairly new, so there may be mistakes in the formalism. As far as empirical evidence goes, a cursory glance suggests the only model that may be threatened is that of black holes in the centers of galaxies, particularly active galaxies, but I'm not sure.

Finally, the Case model predicts observable radiation, so the theory is hopefully verifiable. SamuelRiv 19:26, 14 October 2007 (UTC)

--->***Some Plasma Scientists believe/suggest that BHs do not exist? They seem to have a better explanation on what is really happening out in the Universe. What are your thoughts??? -TruthSeeker 141.117.176.169 (talk) 02:42, 15 December 2007 (UTC)

Splitting the article

The article has reached 140 kilobytes and it's time to split it up, improve the summary style or prune unnecessary text. As an example, the section on major features of rotating black holes is longer than the article specifically devoted to rotating black holes. Any thoughts? --Gimme danger 09:01, 23 July 2007 (UTC)

I partially sympathise, since I suggested splitting the article in April 2007 - but then changed my mind. The problem is that, if we split it, we still have to summarise the content in the "root" article. But the summary would have to be intelligible to non-specialist readers, so it would have to minimise the use of technical terms and explain those it does use - which would make the summary pretty long. The parts I think might be most suitable for splitting out are "History of the concept" and "Advanced topics", which may be of least interest to non-specialist readers. And possibly the sections on empirical evidence for BHs (including methods of detection), which might be fairly easy to summarise in the "root" article. But I think the rest (what BH's are, types of BH and their key features, effects on a trapped object, formation and evaporation) should stay together.

Rotating BHs are an example of this. For example the article "Rotating black hole" is rather terse and it would be difficult for a non-specialist to understand it.

As for pruning unnecessary text, which sections would you drop or shorten? The only one I think should be shortened is the intro. I've already suggested the intro should focus on two points: nothing, not even light or the most powerful spaceship, can escape; Newtonian mechanics predicts BHs but its prediction is based on a false assumption (photons have non-zero rest mass) and fails to predict many of the features, so general relativity is a far better approach.

I've just looked at WP:SIZE and a lot of it seems to be concerned with browser limitations (especially the horrible Netscape 4, now fortunately extinct in the wild). I admit long pages do present usability problems, but Wikipedia's standard page layout mitigates these: the automatic TOC helps readers to find the parts they're most interested in; the ordering of the generated HTML presents content before it presents all the widgets ("Talk", "History" and other links; menu and search box).Philcha 00:31, 28 July 2007 (UTC)

Black Holes renamed

is that true? Article in Daily Redundancy Bull-Dozer 16:53, 23 July 2007 (UTC)

Note the page's subtitle - "The Standard of Excellence in Pseudojournalism". I think someone's making fun of political correctness.Philcha 23:45, 27 July 2007 (UTC)

Although, more seriously, "black hole" is supposed to be quite rude in French (arsehole?). It can't be easy to give a lecture in French on something like "Black holes have no hair". ErkDemon 23:19, 31 July 2007 (UTC)

Les trous noirs n'ont pas de cheveux! But seriously, a native Swiss-French speaker told me that "trou noir" referred to a colored (i.e. any non-white) woman's vagina. SamuelRiv 01:56, 30 October 2007 (UTC)

Matter and Anti-Matter

I'm curious as to poop what might happen if a Black Hole that is made of Matter were to merge with a Black Hole made of Anti-Matter. Could this sort of event be the source of some Gamma ray bursts or other high energy cosmic events? - Fosnez 03:16, 24 July 2007 (UTC)

Try taking this question over to the reference desk. This space is for discussing the article itself, not the subject matter of the article. --Gimme danger 03:37, 24 July 2007 (UTC)

The two black holes will just merge.No explosion,No gamma ray burst,they just merge because mater and anti mater are only matter and antimatter because of the charge of there atoms and since atoms break into quarks and other things no violent explosion will happen. ~~57th street kid~~

The No hair theorem says that the only observable properties of black holes are mass, angular momentum (spin) and electric charge. So there's no difference between a black hole whose mass originally consisted of antimatter (before its gravitational collapse) and one whose mass originally consisted of normal matter. To put it another way, the singularity at the centre is not any kind of matter, since it has no volume. But if you read the article thoroughly, you'll see that it's been suggested that GRBs could be caused by the collision and merging of black holes.Philcha 23:42, 27 July 2007 (UTC)

I think the answer here is we don't know. The annihilation of matter and antimatter is a feature of Quantum Field Theory. The formation and properties of black holes come from a classical theory, General Relativity. To know what would happen if a black hole and an "anti" black hole collide, you would need a unified theory of gravity and particle physics, which we don't unfortunately have. Jpowell 09:40, 8 August 2007 (UTC)

I don't think that's accurate; General relativity is a perfectly good description of large-scale stuff, and we only need quantum gravity to describe very small black holes. The point is, even if the particles inside the black hole could annihilate, they still wouldn't escape the event horizon of the newly-combined back hole. That's why the No hair theorem works; the contents can't matter to the outside world because spacetime is bent too much for anything they do to escape. -- SCZenz 12:37, 8 August 2007 (UTC)

Good point. Jpowell 15:17, 8 August 2007 (UTC)

Intro simplified

I've simplified the intro (as I suggested a month ago) to focus on: nothing can escape, not even light or the most powerful spaceship; Netwonian mechanics and general relativity both predict BHs, but GR is much superior; there is increasingly strong evidence for BHs at the centres of most galaxies.Philcha 01:21, 28 July 2007 (UTC)

Good! These lead sections keep increasing in size as time goes on. Remember the lead sections should be concise. Leave the heavy lifting in the main sections. MegaHasher 07:16, 28 July 2007 (UTC)

I think it was simplified too much, honestly. There are facts about black holes that are quite important that were removed (e.g. Hawking radiation). I also think, while it may be desirable to scale back on the level of terminology and complexity, this went a bit far. I'll play around with it and see what I can come up with. -- SCZenz 07:27, 28 July 2007 (UTC)

Sorry, I preferred my intro. The current intro attempts to summarise large chunks of theory, but this only works for readers who know something of the theory, which: presented a simple definition of a black hole; pointed out that they were predictd centuries ago but the modern analysis is far better; pointed out that they are fairly normal phenomena, not exceptional or catastrophic.Philcha 18:51, 23 August 2007 (UTC)

The fact that it was "predicted centuries ago" is a point of rather minor importance. I don't object to explaining things as clearly as possible, but we have to say what is actually important about black holes, and what's important requires references to other areas of modern physics. To some degree, we have to accept that if people aren't familiar at all with those things, well, that's what we have wikilinks for. -- SCZenz 22:05, 23 August 2007 (UTC)

Perhaps we're talking past each other a bit. You want to reduce the level of complexity, it seems. I want to include the things that are most important about black holes. Maybe we should start from what ought to be in there, and then figure out how to say it? -- SCZenz 07:15, 24 August 2007 (UTC)

Someone simplified the intro to include the words butthole, anus, and poo. I've tried to change it back to what I thought it meant to say, but not sure if I did it correctly, maybe someone can proof it and make sure. LDP —Preceding unsigned comment added by 85.71.202.212 (talk) 23:38, August 27, 2007 (UTC)

Question on hawking radiation

In the Hawking radiation theory, why is the mass that is emitted not pulled back in by the BH's gravitational force?

It can be, but most such radiation is probably going at nearly the speed of light and so exceeds the escape velocity outside the event horizon.

You can also ask questions like this at Wikipedia:Reference desk/Science. -- SCZenz 07:45, 29 July 2007 (UTC)

Most of it does fall back in, in some sense anyway. There's just a small residue that escapes all the way to infinity. I think it's the way the horizon curves that makes the difference; as it gets closer to flat, the escaped energy goes to zero. If it's exactly flat the escaped energy is zero (the Unruh radiation case). I'm not too sure about that, though. -- BenRG (talk) 20:46, 18 February 2008 (UTC)

Why do we believe that Hawking radiation will cause micro black holes to loose mass? If matter and/or anti-matter is added to a black hole then its total mass increases. Hawking radiation defines adding one particle of matter or anti-matter to a singularity and adding the opposite particle to the mass of the universe. Haven't we just witnessed the creation of matter and anti-matter in the universe, balanced by an equal mass in the growing signularity? This question is of utmost relevance as we plan to create Earth's first slow moving micro singularities this year as the result of particle collisions. A single slow moving micro singularity would not escape Earths gravity and would instead absorb the entire Earth. (Please read more from at lhcdefense.org Dr. Walter L. Wagner, nuclear physicist) -- JTankers 2350, 17 Feb 2008. —Preceding unsigned comment added by 69.128.153.189 (talk) 05:58, 18 February 2008 (UTC)

I don't know if this paragraph is just copied from an essay by Dr. Walter L. Wagner, nuclear physicist, but anyway, that particular doomsday scenario can't happen because there's a well-defined conserved energy here. You can't add cake to the hole and eat it too. This is a case where the "virtual particle picture" of Hawking radiation is potentially misleading. In Hawking's original paper he mentions the virtual particle picture only in passing and calls it a heuristic analogy that shouldn't be taken too literally. His actual derivation of the effect is completely different. -- BenRG (talk) 20:46, 18 February 2008 (UTC)

Nothing can escape it, but....

Someone help explain this to me. If Gravity is carried by a theoretical wave-particle (the graviton), and nothing can escape a black hole, how does a black hole attract matter to it? I would think once the event horizon forms, that even a gluon cannot escape, and therefore the black hole should have no effect on anything else. Why isn't this the case? KyNephi 04:57, 5 August 2007 (UTC)

We don't currently have a useful quantum theory of gravity that contains gravitons. So we don't know how gravitons would interact with a black hole. Most physicists expect that a successful quantum theory of gravity would change our understanding of what happens in a black hole, i.e. hopefully removing singularities from the theory.

In the classical theory of gravity, General Relativity, gravity isn't modelled as a graviton, so it doesn't make sense to talk about gravitons escaping from a classical black hole. Likewise in a quantum theory of gravity where gravity is mediated by a graviton, as we don't know what the structure of a quantum black hole would be, so we cannot yet say why gravitons would escape, or whether that statement is even meaningful. Remember also that it is expected that a quantum "black hole" would not be truly black, c.f. Hawking Effect, I don't know if a similar effect could be thought of as responsible for the radiation of gravitons, but it's as good a guess as any.

I'm sorry if that doesn't answer your question, but I think it's the best anyone can do given our current understanding. Jpowell 09:27, 5 August 2007 (UTC)

I have read that since time stands still at the event horizon, as seen from outside, one can feel the influence from all matter that has entered the black hole "lying on the event horizon". Both its mass, its net charge, and its rotation can be measured. This is a classic relativistic view. What quantum effects there are is a little known issue. -- BIL 11:53, 5 August 2007 (UTC)

But classically there isn't any issue with gravitons at all, because gravitons aren't part of a classical theory. Jpowell 22:27, 6 August 2007 (UTC)

Acceleration to keep a constant distance

Hello wikipedia.

The article states (near the 'photo') "An acceleration of about 400 million g is necessary to sustain this distance constantly". If the distance was maintained constantly, wouldn't the acceleration be zero? —The preceding unsigned comment was added by 217.154.95.105 (talk) 10:39, August 21, 2007 (UTC)

The reason the object is accelerating is because the black holes gravitational field is producing a force upon the observer. This force will produce an acceleration towards the black hole, in order to keep the observer to stay in this possition it will need to produce an opposing force equal to the force of the gravitational field. The force being related to acceleration by F = ma. The observer will be accelerating away from the object however it will not move any distance. —The preceding unsigned comment was added by 88.106.51.233 (talk) 09:16, August 23, 2007 (UTC)

To clarify, and I am not sure if this is the case for the photo, a much smaller force is necessary to maintain constant distance by going around the object in a circular orbit than is needed to simply retrorocket away from the hole along the same direction as you are being pulled in. SamuelRiv 01:53, 30 October 2007 (UTC)

Laplace

Could someone please look at Pierre-Simon Laplace#Black hole to see if this is verifiable, and if so to add a reference? Many thanks.Cutler 12:26, 25 August 2007 (UTC)

I added a black hole reference. That still leaves the second part of that paragraph (nebulae as galaxies) unreferenced, though. --Markus Poessel 19:20, 25 August 2007 (UTC)

Approaching the event horizon

At the event horizon, escape velocity is equal to the speed of light. Does that mean that a free-falling observer, starting away at infinity, would reach the speed of light as he crosses the event horizon? Furthermore, he would continue to accelerate to superluminal speed inside the event horizon (before he hits singularity)? This doesn't seem to be consistent with relativity. 192.94.94.105 23:44, 25 August 2007 (UTC)Symyon

These paradoxes are an illustration of why Einsteinian General Relativity's description of black holes is better than the Newtonian version. The concept of escape velocity: (a) only applies to object that are unpowered after being launched, and therefore does not explain why a powerful spaceship cannot escape from within the event horizon; (b) assumes that an object can rise indefinitely far before falling back, so does not fully support the concept of a black hole. Philcha 10:59, 23 October 2007 (UTC)

Pretty much, yeah. I don't know what happens inside the horizon, but as you approach the horizon you approach the speed of light. Observers see you get redder and redder until the radiation you emit is unmeasurable, but you are never observed to drop into the hole. From your reference frame, the singularity is never observable, but you will pass through the horizon in finite time, at which point the outside universe is no longer observable. SamuelRiv 19:37, 14 October 2007 (UTC)

Artists Impressions are terrible

There are currently two "artists impressions" of a black hole in this article. They are both terrible and done by artists who haven't comprehended the nature of a black hole. The first (Image:Black Hole Milkyway.jpg) is simply wrong. A black hole attracts light, therefore the lensing of stars behind the black hole (from the observers point of view) will appear where the black hole is. I.e. there will be NO BLACK HOLE in the page, like there currently is. The secong bad picture is Image:BH LMC.png which does exactly as the first. These pictures are plain wrong and should be removed. There are REAL pictures of the effects of gravitational lenses. Lets include them instead of these spurious, irrelevant and irrational "pictures". --Dumbo1 23:07, 27 August 2007 (UTC)

I agree the artwork is not that good, but you certainly can see a black hole. Think in terms of ray tracing -- a ray coming from the general direction of the black hole can only have originated from inside the event horizon. There are no real images of gravitational lensing by a black hole, but I think these simulations are at least broadly correct. -- BenRG 16:19, 5 September 2007 (UTC)

I actually think the images are pretty good, especially the second one, BH_LMC. Both seem to be created using curved-space raytracing, and so model the behavior of light around the black hole correctly, but the first one (the one in front of the milky way), oversimplifies things by placing the black hole in front of a 2D bitmap, while the BH_LMC image seems to use a 3D field of stars as background, only using bitmaps for the distant LMC, leading to a much more realistic image (I cant find any faults, myself, but I hope to make a simulation myself, if I can get a hold of a star database). Oh, and Dumbol, the real images of gravitational lensing are from weakly lensing objects, where rays of light are only slightly deflected. Try sitting down with a piece of paper, and tracing out a few rays of light in the vicinity of a black hole, and I think you will see how unreasonable your idea of black hole lensing is. Amaurea 08:03, 17 September 2007 (UTC)

blackholes and darkmatter is there a connection?

blackholes and darkmatter, a possible connection???

i'm wondering if micro blackholes as ive just read are infact darkmatter / anti matter all the new age physisists are on about? its just a thought.

i read that theres no real danger of creating a blackhole in a PA and also aparently micro blackholes are created all the time in the atmosphere? or cosmos in general, well anyway they only last .0001 of a second or so.

any comments or opinions are welcome, please add to this section of the disscussion page. CD 23:32, 31 August 2007 (UTC)

Don't know for sure on black holes and dark matter, but the numbers wouldn't add up for how much invisible matter we need in the universe versus how many black holes could have been created in the early universe, much less how much of that needs to be invisible (as in no matter still being sucked in, which would clearly radiate energy). Also, there is firm evidence of exotic dark matter from recent images of galactic collisions (see dark matter for details).

The idea of black holes being created in an accelerator is possible, but the point is that if it could happen at 10^13 eV (as in an accelerator), it has already happened at 10^20 eV (as for cosmic rays - particles colliding with Earth's atmosphere). But again, none have been observed. The article here should have more details. SamuelRiv 01:49, 30 October 2007 (UTC)

Why speculating on black holes at all?

I don't understand the origin of the idea, does it come from observation of actual phenomenons? —Preceding unsigned comment added by 88.162.116.24 (talk) 02:28, 1 September 2007 (UTC)

Black holes were theorized soon after Newton when the corpuscular (particle) light hypothesis took hold and combined with understanding of gravity. Basically, a large mass was hypothesized by people like LaPlace to have escape velocities greater than the speed of light, and pictured a light particle going out and being pulled back in just like if you toss a tennis ball into the air. Then things got complicated (and beyond my knowledge of history) with E+M and wave-based light dominated until general relativity showed that light could be accelerated (in direction, not absolute speed) by spacetime. The modern black hole was a solution to the GR equations. A very, VERY elegant solution. Subrahmanyan Chandrasekhar gave a realistic picture of the formation of a black hole by demonstrating that stars could collapse into them after supernovae, and imaginations took off from there.

To date, no black holes, gravity waves, or Hawking Radiation have been directly observed. However, there is strong theoretical correlation of black hole phenomena to active galaxies, quasars, and other high-energy phenomena in space, and we have estimates of mass and wobbling data in the center of the Milky Way suggesting our galaxy might by powered by central supermassive black holes. SamuelRiv 01:42, 30 October 2007 (UTC)

---

>***Plasma Science seems to suggest that Black Holes do not exist...Your Thoughts?

141.117.176.169 (talk) 02:30, 15 December 2007 (UTC)Truth seeker.

Intro picture

I really like the intro picture. The caption is nice, but still leaves a bit to be desired. Could someone calculate what kind of radius a black hole would have to have to have 10 solar masses? As screen resolutions vary, stating that te view is from 600m is insufficient to figure out the radius. Cheers, samwaltz 01:36, 2 September 2007 (UTC)

A black hole of 10 solar masses has a radius of 2 G (10 solar masses) / c^2 = 30 km, but the apparent radius in the image will be larger because of the lensing. Note that the distance is 600 km, not 600 m. All of the details should be at the URL cited in the caption. -- BenRG 18:00, 5 September 2007 (UTC)

Removed paragraph

I removed this paragraph:

In practice, additional effects are expected to occur as an object approaches the event horizon of a black hole. Hawking radiation is expected to grow brighter, approaching the Planck temperature as an infalling object approaches to within the Planck length of the horizon. Both relativistic and quantum mechanical effects may present a backwards pressure that approaches infinite strength near the horizon, making the fate of infalling objects unclear. This type of back-pressure may cause the region near or within the event horizon to be at very high temperature. As of 2007, there is no scientific consensus about what happens as objects fall into black holes, beyond the fact that it's expected to differ from the picture described by general relativity.

As far as I know, all of this is wrong. Hawking radiation is like Unruh radiation -- you only see it if you're accelerating. Someone freefalling into a black hole won't see any Hawking radiation, at least to first order. There's no scientific consensus that general relativity is wrong about physics at the event horizon, though it might be. -- BenRG 15:56, 5 September 2007 (UTC)

Recent edit by SteakNotShake

I'm sorry if I was a bit brusque backing out some recent additions by SteakNotShake. The most important point is that if edits like these are going to be made, going against the grain of an article, they must cite reliable external sources to support them. Otherwise they will be appear merely to be an editor's own original research, which is not a sufficient basis to add material.

Turning to some of the substance:

To date there has been no experimental verification of the hypothesis that gravity can in fact trap, bend, warp or in any way affect electromagnetic radiation. Because of this, black holes will never be directly detected, and there will never be any direct observational evidence of these hypothetical entities.

(1) It's a direct prediction of Einstein's general theory of relativity, which is considered well tested. (2) Consider gravitational lensing: this would appear precisely to be direct observational confirmation.

Predictions are not experiments. Please cite some experiments showing that gravity has any effect on light. Mere observations combined with speculations ("gravity lensing observations") are also not experiments. Please cite examples of methods used to eliminate the possibility that the conclusions drawn from any "gravity lensing" observation are more than flights of fancy. I have been unable to find any experimental evidence demonstrating any effect of gravity on light. Perhaps you can find some and produce it for us to examine so we can reach a consensus on this issue. As yet the scientific community has no consensus, some believe light can be affected by gravity, others do not. SteakNotShake 14:53, 16 September 2007 (UTC)

Observations of "black hole" candidates typically reveal disks of matter around them. These disks have no reasonable explanation given the omnidirectional nature of gravity, but have a reasonable explanation if they are the result of polar forces like electric and magnetic fields.

The theory of accretion disks is well established astrophysics.

That a theory is widely believed is not the same as a theory being verified. Please cite some experimental verification for this idea that "accretion disks" are matter accreting onto a black hole. Also, if you are up for it, please cite methods that were used to determine that these disks are in fact accreting onto anything and are not produced in some other fashion. Good luck and god bless. SteakNotShake 14:53, 16 September 2007 (UTC)

The most efficient means of producing x-rays, in space or otherwise, is via electric currents, which leads many to believe that these "black hole" candidates are in fact electrically-driven.

Proponents of plasma cosmology suggest observations of "black hole" candidates can be reasonably explained in terms of electrical effects in plasma. Chief among the properties of "black hole" candidates that can be explained simply in terms of plasma effects are the jets of radiation coming from them, which electric theorists identify as Birkeland currents, and their perceived mass, which is explained simply as electromagnetic attraction.

If you're going to make this claim, it needs to be well supported by citations to peer-reviewed material in good journals. (WP:RS). It is not the generally accepted view; whereas the standard gravitational models appear to fit very well with what is observed.

That x-rays are most efficiently produced by electricity is well-verified and there are few who would dispute this claim. You seem to be one of them. Perhaps you can cite some method that is currently used by humans to produce x-rays that is not a direct use of electricity to produce x-rays. I wish you nothing but the best in your efforts, but I fear they will be fruitless. SteakNotShake 14:53, 16 September 2007 (UTC)

I'm sorry if what I did seemed high-handed; but that tends to be the Wikipedia way. Claims that seem contentious or unsupported are apt to be removed from an article, at least until they can be established and defended more fully, on a talk page like this.

And that is exactly what I was doing. The black hole article contained many claims that are entirely unsupported by any experimental verification. Experimental verification is a cornerstone of science. Without it, we delve into hallucinatory terrain. And don't be sorry, you are just doing what you think is right. Just because you are wrong does not mean you are malicious. I don't make assumptions like that, but if the evidence suggests it, I am inclined to believe it. Your apology suggests you think you did something wrong, so perhaps I should take that at face value and believe that you did do something wrong. If so, please don't do it any more and we shall forgive you. SteakNotShake 14:53, 16 September 2007 (UTC)

Best regards, Jheald 09:19, 6 September 2007 (UTC)

And best regards to you as well. Again, you are trying to defend material in this article that is entirely unsupported by experimental verification. I don't want to call it weak, but that's not exactly a strong tactic. I fear you are on the losing side here. Perhaps you should do some more studying before you recklessly revert material that you clearly don't understand. SteakNotShake 14:53, 16 September 2007 (UTC)

Perhaps you should do some more studying before you recklessly insert material that you clearly don't understand. Particularly on what an "experiment" is, with regards to the bending of light by gravity. --Michael C. Price ^talk 15:12, 16 September 2007 (UTC)

Thanks for your concern on this issue, but my simple challenge reveals the bias you seem to share with other users here. If you know of some experimental verification for this idea that gravity can have any effect at all on light, please cite it here for us to examine and we can reach a consensus on this issue. I'll wait a reasonable amount of time and then I will simply make the necessary changes when you fail to produce references to such experiments. SteakNotShake 15:19, 16 September 2007 (UTC)

Eclipse data, starting in 1918/9. If you claim it was not an experiment I will not respond. --Michael C. Price ^talk 15:24, 16 September 2007 (UTC)

If you're referring to Eddington's fraudulent claims about his observations of an eclipse, it's widely-known that he cited accuracy well in excess of the capacity of his instruments to deliver. That is known as fraud. And as you seem to already know, it was not an experiment, but mere observation. 15:35, 16 September 2007 (UTC)

I believe it to be a good suggestion that SteakNotShake focus his anti-relativistic attitudes into publishing an article on the complete disprovement of General Relativity, Black Holes and the definition of 'experiment and prediction', and subsequently formulate a unified theory that satisfies all of the above better than current data he so arrogantly denounces. ArdClose (talk) 18:07, 20 December 2007 (UTC)

Intro

This image is nothing more than a Photoshop filter performed on a picture of outer space and does not accurately depict or describe a black hole at all. I suggest the picture be removed or perhaps replaced with a line drawing or 3D picture of the structure or geography of a black hole; something like [1] seems worthy of consideration. Having an obviously filtered picture of outer space created without input or data from research conducted about black holes looks hobbyistic or amateur at best and diminishes and embarrasses Wikipediea — espcially when this article is the first Google hit for the search term "black hole." Trollaxor 04:46, 7 September 2007 (UTC)

you are right, the picture in the intro is misleading. note that the falling mass on the black hole will be radiative in all direction and it will not be a two dimensinal picture with a "hole" in the middle. from 600 km I dont think the black hole will "look" anything like a black disk with local (gaussian ) distortion (as depicted in the photo). I am taking down the image Jeroje 10:56, 7 September 2007 (UTC)

Thank you. The entry looks much more professional and wholesome without that bit of Photoshop monkeyshines. Trollaxor 20:26, 7 September 2007 (UTC)

The source for that image claims that it was computed exactly, and I see no reason to doubt that; it looks correct. The image you linked, on the other hand, looks like an artist's impression by an artist who doesn't know much about black holes. The fact that such images are common in popular science magazines doesn't mean we need one on Wikipedia. But you're right, the image does look really bad. Maybe what it needs is some touching up in Photoshop, to make it look less obviously computer generated. At the very least it could use some CCD noise in the center disc. -- BenRG 11:11, 7 September 2007 (UTC)

Thank you for the link. While I do not argue that the source claimed to have based their graphic transformations on accurate data, I can attest that I just now finished using Corel Painter 7 (released August 2001) to do nearly-identical transformations to the original picture of the source's series. At best, they're using some number to adjust the strength of the filter used in those pictures. While technically being based on relevant data, that is an inaccurate use software not designed for interpreting the effects of the strength of black holes. Trollaxor 14:48, 7 September 2007 (UTC)

What filter was it? Keep in mind that it's called "gravitational lensing" for a reason. Any rotationally symmetric lens will give results similar to this image for reasons of symmetry alone. -- BenRG 22:28, 7 September 2007 (UTC)

The picture in the intro was not the gravitational lensing one, though the gravitational lensing photo is also not correct. Gravitational lensing would not necessarily have any rotational symmetry, it will depend on the distribution of matter in the vicinity of black hole just like a lense with a variable refractive index. gravitational lensing gives rise to split images of same objects or highly distorted images.IMHO it never makes the space look like a "mint hole" as depicted by the photo. I guess we can get a schematic image of a point type simple singularity to represent black hole. As we cannot sketch a three dimensional object in two dimension we must have a surface representing the time-space and a singularity or a pinch point will be the best we can do more or less like this until we get an observatory image. Jeroje 06:12, 8 September 2007 (UTC)

The picture in the intro did show gravitational lensing by a black hole, and was the only image in the article that did, making it "the gravitational lensing one" for all practical purposes. As you say, the image that currently illustrates gravitational lensing actually is wrong and should presumably be removed. Actually I think the other image is fine. It's harder to see the actual lensing, but it looks better at least.

I don't mean to be blunt, but do either of you understand how to compute images like this? Can you write down the geodesic equation for a test particle moving in a Schwarzschild vacuum in Schwarzschild coordinates? Do you understand how to translate (x,y) pixel coordinates in a rasterized image into initial conditions, and how to map the t → ∞ limit of the geodesic to pixel coordinates in Axel Mellinger's sky projections? I know enough about general relativity and ray tracing to see that the disputed image looks essentially how an image computed that way should look. The only reason I'm not sure it's correct is that I can't be sure they didn't make a mistake when calculating the deflection angles. An image based on incorrect deflection angles would still look broadly the same. But I think they probably got it right, because my impression from reading that site is that they understand the principles involved. My impression from talking to you two is that you don't understand the principles involved. The only arguments I've heard are (a) that this doesn't look like other gravitational lensing images you've seen, and (b) that it looks like they cheated by using a stock graphics filter. The first objection is irrelevant, since it looks like it should. The second objection appears to be an accusation of academic fraud, and I see no reason to believe it.

The best way to resolve this debate would be to recompute the image and compare. I really don't want to do this because it would be a lot of work. But if someone else wants to tackle it, this paper says that the deflection angle is given by $-\pi +2\int _{0}^{u_{0}}{\frac {du}{\sqrt {a^{2}-u^{2}+2mu^{3}}}}$, where $a={\frac {1}{r(s)^{2}}}\left(1-{\frac {2m}{r(s)}}\right){\frac {t'(s)}{\phi '(s)}}$ (an invariant of the motion) and $u_{0}$ is the positive root of $a^{2}-u_{0}^{2}+2mu_{0}^{3}=0$. I'm not even sure I got those details right, which is a big part of the reason I don't want to do this. -- BenRG 14:37, 8 September 2007 (UTC)

That you know the above and think the images look like how those data would compute is impressive, but misses the fact that Photoshop and similar were not built to interpret mathematical data pertaining to black holes. I know what the result of letting a child sleep with a beehive is but also know the child should instead cuddle stuffed animal. So again, as I expressed many times in the above posts, while the images in question may have been made using numerical values extrapolated from actual black hole data, that does not make the images accurate or relevant since the tool used to interpret the data was not built to do so. Recomputing the data would be a fruitless waste of time. Trollaxor 14:41, 15 September 2007 (UTC)

Well said, BenRG. There seem to be a lot of people who, upon seeing these carefully raytraced images, instinctively think that Photoshop was used, and who know neither Scwartzschild spacetime or the geodetic equation. That said, I will switch the places of the two raytraced images, since the second one seems to be based on more accurate initial conditions (the first seems to raytrace a single 2D bitmap oriented perpendicularly to the line of sight, while the second one seems to raytrace a 3D field of stars in front of a remote bitmap). But both images seem to do their raytracing correctly. Amaurea 08:24, 17 September 2007 (UTC)

So it seems you have removed one of only few more or less reasonable pictures of BH. As of my point of view, this is not Hawking's graduate-level lecture but something that can put any light on cosmological topics in popular sense. If you want to remove it, please do it when you will have something for replacement. As for now, please consider preparing more strict image or splitting the article on "more popular" and "more scientific" parts. -- 83.27.120.117 16:00, 8 September 2007 (UTC)

The objection seems to be related to the solid disk in the center, and has been voiced elsewhere in this discussion. Without being active in GR or astronomy research, I will say that the image is not trying to show what a black hole would look like in "real life" (if you want to see what they might actually look like, put up a picture of an active galaxy), but it is a mesh of several details of the model, namely gravitational lensing and the "hairless" theorem. Obviously if matter is accreting into the hole, the horizon would be obscured - this image seems to model an isolated, nonrotating hole, and is pretty accurate at that. SamuelRiv 18:51, 14 October 2007 (UTC)

Good faith edits

Hey all. An IP recently introduced these edits into the lead. Its clumsy, grammatically poor, unreferenced and for all I know repeats information already in the article. However, I'm loath to revert it as the edits seem to be in good faith. Could someone with more experience on the topic check if these edits are at all necessary/need to be reverted/can be incorporated into the text properly. Thanks. Hammer Raccoon 10:20, 10 September 2007 (UTC)

No matter, someone bolder than me reverted. Hammer Raccoon 11:58, 10 September 2007 (UTC)

Hello

I edited this page before realizing it was a featured article. I was bugged by some mistakes, so I fixed them. In case my changes are too poor in grammar or whatnot and get reverted, here's what was wrong:

1. The RHIC "Fireball" is not a black hole at all, and it is very well confirmed. It is analogous to a black hole by AdS/CFT. It is not speculative, and the analogy with black holes, although it hasn't had time to be judged as well accepted, is not very controversial.

2. Classical black holes in the Bekenstein Hawking picture have infinite entropy, not zero entropy. The change in entropy when you add heat to a zero temperature object is dS = dQ/T which is infinite. The Hawking entropy goes to infinity when h-> 0.

3. Hawking's bet is only significant as a media event. By the time Hawking did his calculation, many suspected that black hole evolution was unitary. This is not to discount from the historical importance of the information paradox, which led directly to holography and AdS/CFT itself. Nor is it meant to diminish Hawking's stature.

4. The historical discussion misleads: A Laplace style black hole has an event horizon. It does not assume that light has a rest mass, only the law of "universal free fall", which is a principle in both Einstein and Newton's gravity.

5. More historical inaccuracies: The wave-particle duality is a purely 20th century thing. The debates in the old days about whether light was a particle or a wave were all based on experiments that never showed one scintilla of evidence for the particle interpretation. The first experiment that showed photons unequivocably is the blackbody radiation. So before the 20th century, or at least the late 19th, it is not appropriate to say that the scientific community went "back and forth" between the two. They didn't. They just went forth. Light is a wave. End of story.

The fact that statistical mechanics requires light to be a particle because of the blackbody catastrophe might have been realized by some people in some vague corners of their mind. But to write about this is speculation, and does not, in my opinion, belong on the page.Likebox 02:06, 14 September 2007 (UTC)

Speculation about light as a particle goes back (at least) to Newton.--Michael C. Price ^talk 15:08, 16 September 2007 (UTC)

That's true, but that was just Newton and followers hoping and speculating. This stuff got sorted out, and it was sorted out as "light is a wave". All of Newton's experiments could have worked with light as a wave, but he was hoping it was a particle so it would be like matter. I don't think it's right to say the scientific community went "back and forth". The fact that one guy says its a particle is not a sign of a scientific controversy, even if that guy is Newton and even if he turned out to be partly right two hundred years later.

So for example, the wave people said that if you machine a perfect disk, there will be a bright spot in the middle of the shadow. The particle people thought shadows were blocked paths of rays, so they used this prediction to ridicule the wave theory. Until the bright spot was observed.

In refraction, light bends, and if it is moving into a material where it moves more slowly it bends inwards. In Newtonian mechanics, if a ball is rolling along the sidewalk and it slides down a smooth curb to the street, it gains speed and it also bends inwards. But then, the ball moves faster in the region where it bends in. So the particle people predicted that the index of refraction means that light is moving faster in the medium where it refracts, and the wave people said it was moving slower. You can guess how that turned out.

The fringes in Newton's experiments which he attributed to "pulsations" of the particle were clearly due to interference. All his pulsation stuff was smoke and mirrors. In order to make a particle theory of light, you need to understand relativity and you need to understand quantum mechanics. Then it makes sense why a particle-wave of a rolling ball bends inward when it goes faster, but a particle-wave of light bends outward when it goes faster. Just my 2cents.Likebox 01:26, 18 September 2007 (UTC)

6. A strangelet is strange matter, it is not a type of black hole. The behavior of the two objects are similar. It is misleading in the current version.Likebox 02:48, 14 September 2007 (UTC)

I have only passing familiarity of the Laplace black hole, but a cursory glance suggests Newtonian mechanics breaks down with a zero-mass particle (photon), as the equal free-fall requires nonzero masses to cancel in the gravitational potential. Mathematically, this is a removable singularity for a zero-mass object. Has this ever been resolved in Classical Mechanics? Obviously in GR there is no problem.

And I don't believe blackbody demonstrated "unequivocably" the light quanta (photons), as equivalent models of blackbody were established in the 19th century using stat mech and some informal math. Certainly Planck's model was much more elegant, but I believe (not at all certain - I'm not well studied in history of physics) that quantum field theory was necessary to prove the quantization of light. Certainly it proved the quantization of most everything else. SamuelRiv 18:36, 14 October 2007 (UTC)

Wont it all eventually be sucked in?

Hello, I was just thinking, after reading this entire article. Eventually, wont eveything be sucked into a black hole and then the black holes will collide untill you have the singularity? Or does this not work? ALso, i don't like the idea of being so close to a black hole =S. —Preceding unsigned comment added by MVG1234 (talk • contribs) 22:57, 5 October 2007 (UTC)

That's what happens in the big crunch scenario, but it doesn't look like there's going to be a big crunch. Black holes are not as dangerous as many people think. They have the same gravitational pull as an ordinary object of the same mass. The trick to not falling into a black hole is the same as the trick to not falling into a star: don't head directly toward it. If the article doesn't clarify this, it probably should. -- BenRG 10:11, 6 October 2007 (UTC)

Internal links etc

Can the Wikilinks at the end be included (and the article in the latest New Scientist)?

As this page is somewhat long can it be divided up. Jackiespeel 23:15, 10 October 2007 (UTC)

2 event horizons

when i was reading this (and in my last year of high school im not exactly too savvy on this stuff) and got to the secion on rotating black holes it goes straight to the idea of 2 event horizons. have i misread this or does it mean the ergosphere or what? cos under the heading "two event horizons" it starts talking about inner and outer ones. This has me really confused about it and thought i should just mention it and hope i didnt miss something ^^ Helmet Shell 14:07, 18 October 2007 (UTC)

You were very right to question that nonsense. I registered explicitly so that I could remove it. Unfortunately, it looks like I have to wait a while, or something. For anyone who can, please correct these mistakes that (I now see) have been on the site since March 17! Both sections "Two event horizons" and "Two photon spheres" should go. It looks like the ergosphere section could use similar cleanup, too. (I suspect the confusion was caused by a poorly written outside source, but was contributed earnestly.) --JerryBomb 23:22, 21 October 2007 (UTC)

Welcome to Wikipedia (or non-IP-address-hood). I don't think those sections should be deleted, though. It's true that the standard textbook rotating black hole metric (Kerr metric) has two event horizons for lower spins and no event horizon for higher spins. I don't know if it's true that there are two photon spheres, but it seems plausible enough. I fixed one mistake (or poor choice of words) and deleted a sentence that didn't make sense to me ("This beam will then split itself in two and both pieces will move into the Hole."). -- BenRG 00:11, 22 October 2007 (UTC)

I agree there's a naked singularity for super-maximally spinning Kerr holes, but that's almost certainly unphysical -- it's a fun little mathematical curiosity. Here it is presented as physically relevant fact.

Siumilarly, you have to extend the spacetime in order to find "two horizons". And in that case, you get as many horizons as you want, though these are Cauchy horizons -- not strictly event horizons. The extended spacetime is not thought to be at all relevant to our Universe. It is a toy model with no applicability to astrophysics. The $r_{-}$ and $r_{+}$ that you see in the non-extended Kerr solution are coordinate singularities just like r=2M for Schwarzschild.

I really think those sections should go, or be rewritten and moved toward the bottom, because they really are finer points that are badly explaimed don't belong in that place. The article is full of wishy-washy statements like "their wavefunction must spread", but these two sections are egregious. Somebody (with permission) should really reorganize this page. --JerryBomb 00:37, 22 October 2007 (UTC)

Okay, I'm convinced. I deleted both sections, though I'm not sure it's materially reduced the general awfulness of the article. (I think the waiting period for semiprotected articles is four days after registration, by the way. Please rewrite everything.)

$r_{-}$ and $r_{+}$ may be coordinate singularities in Kerr coordinates, but there are real Cauchy horizons "there" even if they're not covered by the coordinates. I've seen them both called event horizons, though honestly I've never been sure what exactly counts as an event horizon in these discussions. I feel like the past, er, event horizon of the Schwarzschild solution deserves that name by symmetry, and if that's an event horizon then surely the $r_{-}$ surface should be one too. Not that I suppose it matters, since neither one has any physical significance. -- BenRG 01:52, 22 October 2007 (UTC)

Alternative black hole models

I want only mention that all black hole doubles are excluded through theoretical calculations. See [2] The recent theory of Krauss et al. is also scientific bulls... because they were simply not able to interpret the used coordinates in the right way. See [3]

Please explain "not able to interpret the used coordinates in the right way" in a way that specifically relates to the CWRU paper. The slideshow you linked was a very interesting resolution of the horizon paradox (summary: an infalling particle expands the hole horizon simultaneously as it collapses, and can theoretically pass the new horizon before the hole expands in outside observer time, thus eliminating the paradox.) I will try to find the guy's paper and look at the details, but my first objection comes from the problem that the particle size is much larger than the expansion in hole radius, and combined with quantized length scales it makes me a little suspicious.

AFAIK there is no scientific debunking of the CWRU paper yet. I think it deserves to be taken seriously as a paradox resolution scenario. Or perhaps we should just add a section on paradoxes and resolutions which gives all of these theories their due time. SamuelRiv 01:32, 30 October 2007 (UTC)

I have created a new page for alternative black hole models at nonsingular black hole models. Hopefully we can continue such discussions there. SamuelRiv 19:19, 3 November 2007 (UTC)

I will explain why the theory of Krauss et al. is false. In their paper [4] they argue (let me cite:)

we verify the standard result that the formation of an event horizon takes an infinite (Schwarzschild) time if we consider classical collapse

This argument is not true and shows that they have no idea of GR. What GR tells is only that it takes an infinite amount of time for light rays to reach an asymtotic observer, when it would be emitted at the event horizon. Krauss confound this fact with the erroneous belief that the formation of the event horizon takes an infinite time. I would like to go into detail and use a model of Andrew Hamilton based on this paper [5] in order to falsify the stupid and dangerous (lots of people with less physical backround will believe him) ideas of Krauss et al..

Lets assume spacetime behaves as a fluid and can flow with any velocity. Lets further assume that this fluid is inhabitated by lots of observers which can only communicate through pressure waves with the velocity v and cannot exceed this velocity with their vehicles. If there is a sink hole (analog to the black hole) inside this fluid universe, then the fluid will move with higher and higher velocities into the abyss. At some point the velocity of the fluid will excess the velocity v (For the black hole that means that spacetime will collaps with a speed faster than c behind the horizon. That is no problem for GR because we as asymptotic observers cannot see this superluminous velocities because it happened outside our own horizon or in other words inside the black hole. Even more strange is the fact that there are regions in the universe which move with speeds greater than c away from us but nevertheless we cant observe them because they are behind the cosmic event horizon). So let me come back to the fluid universe. If there is a stupid observer (call him Lawrence K.) who falls into the sink hole he wouldn't recognize when he crossed the point where the velocity of the fluid becomes bigger than v. He can do what he wants. There would be no possibility to tell the otside world of his trip into the hole. Any pressure wave would take an infinite amount of time to reach the other observers when it would be emitted at the sound horizon (event horizon). What I want to say is that of course one cannot see a black hole because it takes an infinite amount of time for light rays to reach us from the horizon (that is "what makes it black") but that does not mean that it takes an infinite amount of time for the event horizon to form.

In a physical sense it is right to say that Krauss interpred the used coordinates in a wrong way. In the next days I will erase the mention in the main article that some guys from the Case Western Reserve University have disprooved the existence of black holes because their arguments are totally wrong. The same holds true also for objects like MECOS...

Hope this helps —Preceding unsigned comment added by 212.201.71.52 (talk) 21:36, 16 February 2008 (UTC)

Simulated views of a depressive alcoholic kneeing in front of the toilet

Scientifically totally wrong:

• http://commons.wikimedia.org/wiki/Image:Black_Hole_Milkyway.jpg

A black hole is a 3D- (or 4D, if you are getting older) object and this is not, as described "viewed from a distance of 600 km" but a cross-section of whatever.

The whatever: a black hole is due to the influence of the rest of the existing universe a EXTREMLY radiating "thing" in any wavelength, especially the hard ones. And some other material things. Material things or the rest of them are rotating around it at very nearly the speed of light. And even when its a small black hole, 600km is very near, its RADIATING. So why dont take:

• http://commons.wikimedia.org/wiki/Image:Milky_Way_Galaxy_center_Chandra.jpg

Even our milky way has a black hole; but it isnt black, but extremly bright

• http://commons.wikimedia.org/wiki/Image:Close-Up_Look_at_a_Jet_Near_a_Black_Hole.jpg  : A better explaining picture
• http://commons.wikimedia.org/wiki/Image:Dust_disk_and_massive_black_hole_(GL-2002-001188).jpg
• http://commons.wikimedia.org/wiki/Image:Sig06-019.jpg
• http://commons.wikimedia.org/wiki/Image:M104_ngc4594_sombrero_galaxy_hi-res.jpg Shows the main visible things: Brightness
• http://commons.wikimedia.org/wiki/Image:M87_jet.jpg, shown already.

This pictures shows REAL subjects and are probably the best real view of black holes ever possible. Simply a radiating, emitting object with the hole hidden deep inside. Probably nobody ever gets there alife to take a photo. Carrying it out is another difficulty, even by a strong transmitter. Good thing: you dont need a high ISO sensitivity of the camera, you even dont need lenses or any stuff. Exposure-time even at 50 ISO is quite low. If you "see" the black thing, it is probably a barrier: on the one side extreme radiation, on the other???

Another wrong thing is:

• http://en.wikipedia.org/wiki/Image:BH_LMC.png

This is a simulation in Photoshop, not in Mathcad or others. The deep depression of the artist (sorry, no scientist) drawing such black things in the center (of his life?) is scientifically too wrong to be debatable.

Black holes are reality, show it.

195.4.211.88 09:09, 2 December 2007 (UTC)

Fine, put up a picture of any spiral galaxy or quasar then. The point of these images is to show how a non-visibly-radiating non-accreting black hole would look. In that sense they are accurate. Chill out. SamuelRiv 12:44, 2 December 2007 (UTC)

IANAA, but I think most black holes do look like that. The black holes we have pictures of are not a statistically random sample; they consist solely of those radiating strongly enough for us to see them. Presumably there is a large population of stellar-mass black holes that have no accretion disk and are completely invisible at astronomical distances. Not that the article shouldn't have real photos in it. -- BenRG 18:55, 2 December 2007 (UTC)

That is not true. Black holes form by supernova, and a significant amount of matter during the explosion gets trapped in orbit around the black hole. Furthermore, if there were a number of black holes without accretion disks, we would see it from gravitational lensing. SamuelRiv 21:02, 2 December 2007 (UTC)

Actually it is pretty hard to detect stellar mass black holes by gravitational lensing. Note that the lensing effect of a stellar mass black hole is equal to the lensing effect caused by a stellar mass star. This, by the way, is exactly what the people looking for MACHO's are looking for. —Preceding unsigned comment added by TimothyRias (talk • contribs) 11:33, 19 March 2008 (UTC)

Thank you SteakNotShake

Now can this article please state a little more clearly that "black holes" are still entirely hypothetical and their existence has never been experimentally confirmed? Because right now it seems to suggest that these "black holes" are actually real.

I think someone intelligant enough to understand the subject matter in the first place would realise they are a hypothetical and exotic solution to a theory. ArdClose (talk) 18:13, 20 December 2007 (UTC)

I'm afraid this is no longer the case. As explained in the section 'black hole candidates', the evidence for the existence of black holes is now regarded as fairly conclusive. Algebraist 01:28, 17 January 2008 (UTC)

Frame of reference in time of a black hole? Gravity / Time

If a black hole has an infinite density, does that mean that a primorial black hole is still experiencing either the moment of the big bang or very shortly after the big bang? —Preceding unsigned comment added by 207.45.240.18 (talk) 19:13, 10 December 2007 (UTC)

Does anyone editing the page have a B.S. or higher in PHYSICS?

Most editors have a Ph.D., some are professors Count Iblis (talk) 02:36, 11 December 2007 (UTC)

Infinite Gravity

A black hole does not have "infinite gravity". The gravity of anything is directly proportional to its mass. A black hole does not have infinite mass.Primium mobile (talk) 01:53, 13 December 2007 (UTC)

First let's remove an ambiguity. "Black hole" usually refers to the space bounded by the event horizon, and the gravitational attraction at the event horizon is finite but great enough to make escape impossible. But 2 out of 3 of the relevant physical theories conclude that gravity is infinite at the centre. In Newton's theory of gravity, gravitational force is proportional to the masses of the 2 bodies and inversely proportional to the square of the distance between them. The mass at the centre of a black hole has zero radius, so the gravitational pull at its surface is infinite (any non-zero number divided by zero = infinity). General relativity reaches the same conclusion, but by different reasoning (the curvature of space-time is infinite at the centre). Quantum mechanics apparently doesn't allow a non-zero mass to have zero radius and therefore would not predict infinite gravity at the centre, but we don't yet have a physical theory ("quantum gravity") which combines general relativity and quantum mechanics. Philcha (talk) 12:03, 13 December 2007 (UTC)

I wasn't really paying attention when I first read this. Looking again, I see that it said that there was infinite gravity at the singularity. With infinite space-time curvature there is probably going to be infinite gravity. However, it is not proper to say that a non-zero number divided by zero is infinity. That's like saying that infinity minus infinity is zero. Infinity is not a number, it is a concept. If you try to do an operation with any number over zero (ie 6/0) the answer is that it is undefined. If you say that the answer is infinity then you are saying that an infinite number of zeros will equal the non-zero number. That is nonsense.Primium mobile (talk) 21:47, 14 December 2007 (UTC)

We could get into arguments about the meaning of infinity here - I know there are different types of infinity (and that's about as much as I know about the mathematical theory). But the simplest definition of (the simplest kind of) infinity is a number larger than any that you can write in any notation that does not use an infinity symbol. Gravitational attraction at the singularity meets that spec - it keeps on increasing at an increasing rate as the radius tends to zero. Philcha (talk) 15:36, 16 December 2007 (UTC)

I'm not arguing with you about the gravity. When I first read that, I was considering the black hole to be everything beyond the event horizon. I wasn't considering it to be only the singularity. I agree that infinite curvature produces infinite gravity.Primium mobile (talk) 07:35, 17 December 2007 (UTC)

I think we shouldn't talk about infinite gravity, even at the singularity. Everywhere except at r=0 you need infinite mass for an infinite gravitational attraction, which is not the case here. The gravitational force is a vector with a direction. At r=0 there is no direction for gravity because your are already at the exact same position as the source of the force. Argider (talk) 13:55, 29 January 2008 (UTC)

Negative Black Holes

Is it possible sdf that black holes could be made up of compacted negative matter, in some and matter in others. The reason I ask this question is that if there could be in fact be different charged black holes, a theory of the origin of the Big Bang could be made. One could be made through the fact that two different charged black holes meeting and coliding would cause a very big explosion such as a Big Bang. ARedens (talk) 04:22, 16 December 2007 (UTC)

This question, and many of those asked previously, don't belong on this talk page. Please ask them on the Reference Desk instead. The talk page is for discussion regarding improvements to the article, not discussion of the subject itself. --Philosophus ^T 15:39, 16 December 2007 (UTC)

Need to agree scope and technical level of Intro

The Intro has been extremely volatile over the last 6 months - different editors have different ideas about what it should contain and how technical it should be. On 24 August 2007 SCZenz very sensibly proposed we should discuss this and then create an intro that fits the consensus view. Let's do it!

Here's my bid:

• Style: simple, aimed at bright curious teenagers with little previous knowledge of the subject and no maths beyond simultaneous and quadratic equations. The body of the article can explain and / or cross-link to the more advanced concepts and techniques.
• Content
  • Basic practical / empirical definition - gravity so strong that neither light nor the most powerful spaceship can escape.
  • Predicted by Newtonian mechanics and by Gen Relativity, but the GR version is far superior, e.g. explains why powered objects can't escape. Reason for this: many popular accounts are essentially Newtonian, relying on the concept of escape velocity, and we need to tell readers up-front that there's more to the subject - preferably in a way that motivates them to read further.

Newtonian physics doesn't actually predict Black Holes. My experience is that popular semi-Newtonian way of introducing black holes, just confuses the hell out of most people. It is probably best not to mention this at all. (TimothyRias (talk) 12:38, 19 March 2008 (UTC))

• • BHs are a normal phenomenon, not freakish or particularly threatening. Large stars eventually become BHs. Galaxies have supermassive BHs at their centres. Lots of observational evidence. Philcha (talk) 16:31, 16 December 2007 (UTC)

It is very important that it says black holes are theoretical, which they are. They are a construct/ model and we assert that observed phenomena agree with these predictions, be we cannot say with certainty that black holes indeed exist. Let's be completely honest and professional fellow physicists. —Preceding unsigned comment added by 76.22.151.40 (talk) 02:57, 17 December 2007 (UTC)

That is correct from the point of view of a ruthlessly consistent philosopher. But from that perspective everything is theoretical, including your existence (from my point of view)! See the works of René Descartes, George Berkeley, David Hume and Immanuel Kant. I don't think the Black hole article can afford to go that deep - readers' minds would get the bends. Philcha (talk) 14:53, 5 January 2008 (UTC)

It is not only correct, but also inline with what we mean when we say a black hole is such and such. In such a situation we are talking about the hypothetical object as predicted by gravity theories. We are not talking about empirical facts as observed from real astrophysical objects. This something that is not at all clear for a casual reader, who will start wondering 'How did they find this out?'. (TimothyRias (talk) 12:38, 19 March 2008 (UTC))

Black Hole Parameters

I'm not happy about User:Harshil8's insertion of this section: its content is covered in various sections in other parts of the article, notably "No hair theorem"; it disrupts the flow from "Features of non-rotating black holes" to "Features of rotating black holes". How do others feel about this? Philcha (talk) 12:57, 18 December 2007 (UTC)

It looks out of place to me and is all covered by the no hair theorem section. Delete it. --Michael C. Price ^talk 08:29, 13 March 2008 (UTC)

This section is missing all of the actual numbers and variables. For example: "The mass parameter is equivalent to a characteristic length , or a characteristic timescale , where denotes the mass of the Sun." What length? What timescale? What denotes the mass of the Sun?

To make sure it wasn't a problem with my browsers, I looked at the source, and there's nothing but a space.

More examples: "For a stellar mass hole this is of order , while for a supermassive hole of , it is thousands of seconds." "... the horizon is at radius ." "... the gradient of the gravitational acceleration, as in Newtonian theory: ."

As far as I can tell, this section was added by Harshil8 in http://en.wikipedia.org/w/index.php?title=Black_hole&oldid=178677465, who noticed and fixed a few of the gaps in the next revision, but left dozens more unfixed.

This is sad, because there would be a lot of good information in this section, if the information were actually there.

The section also seems to be misplaced, but that's a less serious issue. --75.36.142.34 (talk) 17:00, 23 December 2007 (UTC)

The missing equations suggest a sloppy copy-and-paste job from another website. I did a web search and found what appears to be the source. I'm not sure whether this is a copyright violation, but probably it is. -- BenRG (talk) 08:26, 24 December 2007 (UTC)

characteristic distance

Hello,

I think "characteristic distance" in the paragraph "Mathematical theory of non-rotating, uncharged black holes" should either have a link or be explained. Thanks. Randomblue (talk) 12:49, 17 January 2008 (UTC) jimmy and beñato =japn bander —Preceding unsigned comment added by 80.39.98.175 (talk) 11:10, 21 January 2008 (UTC) $Insertformulahere$

Micro black hole escaping from a particle accelerator

The main article section, "Micro black hole escaping from a particle accelerator" consists of paragraphs that repeat one another and struggle to get to a point. Can someone who knows something about black holes please rewrite that entire section?—GraemeMcRae^talk 09:13, 2 February 2008 (UTC)

The second, third, and the second part of the fourth paragraph (i.e. the entire of the "against LHC" veiwpoint) is also lacking in any citations. The section "Conversely, the relatively slow speed of collider-produced micro black holes..." repeats a point made earlier. 82.41.14.153 (talk) 21:13, 7 February 2008 (UTC) unregistered user

overview

its strange people my age to be intrested in these kind of things, but its so intresting. so basically anti-matter is created in black holes because...those things...i forget, they are stripped away to create anti-hydrogen, helium etc. and the anti-matter pulls on matter and brings it to the center of the black hole which makes it dense (i.e. the zero volume) and with high mass=high gravity and ergs. are energy and energy can be absorbed so that is why light is absorbed. So the objects properties like hydrogen for example, will be taken in and anti-hydrogen will be made so it will continue absorbing hydrogen and get denser and denser. BUT HOW ARE THEY CREATED??!?!! PLZ ANSR!! D:<

Refer such questions to the reference desk, and cut out the caps, AIM-speak, and emoticons if you want to look sane. For the record, I suggest you reread the article and forget everything you've heard about anti-matter, as that isn't how a black hole works. SamuelRiv (talk) 17:48, 6 February 2008 (UTC)

An observer passing through the Event Horizon

I see this often in books, and now on the Wikipedia. "From the viewpoint of the falling object, nothing particularly special happens at the event horizon." I think these authors forget that we are not zero-dimensional beings. The space within a black hole is like an information diode - information can flow towards the center, but not back. So if I (the observer) where to fall feet first towards a black hole, I would notice that as I pass the horizon, my feet go numb. What is worst, as my brain passes the horizon, the half inside the horizon can no longer communicate with the half outside. I think I would notice this. Joemurphypgh (talk) 13:29, 8 February 2008 (UTC)

Your feet won't go numb as you fall through an event horizon. In fact you are falling through event horizons right now without any ill effect. For example, the 3-surface defined by x=ct in Minkowski space is an event horizon. Information can only cross it in one direction, but you won't notice anything strange when you cross it, because there won't be anything strange; the crossing region is just like every other region in Minkowski space. Black hole event horizons are the same. See Rindler coordinates for the special relativistic analogue of a black hole; it's amazing how much they have in common. The article doesn't mention it, but Rindler horizons even emit Hawking radiation, though it's called Unruh radiation in that context. -- BenRG (talk) 21:55, 8 February 2008 (UTC)

I'm sorry - You're right. I was applying what an observer outside the black hole observes with what an observer free-falling into the black hole observes. The two frames of reference are not the same, and the free-falling observer would not notice the local curvature of space until they were much closer to the singularity. —Preceding unsigned comment added by Joemurphypgh (talk • contribs) 16:06, 11 February 2008 (UTC)

The Big Bang!

I think think think think that a black hole could devour everything in the universe including other black holes and after there is nothing left in the universe it will start to devour itself and it will become a tiny extremly dense particle and with nothing to sustain it it will begin to expand outwards again like the big bang. Then more black holes will be created somehow and the cycle will repeat. Alexthegreatest —Preceding comment was added at 14:56, 12 February 2008 (UTC)

Black holes don't really "devour" things. It's harder to fall into a solar-mass black hole than to fall into the Sun, because it's smaller. You have to aim pretty carefully. Conservation of angular momentum is your friend (or enemy if you have a death wish). -- BenRG (talk) 17:42, 18 February 2008 (UTC)

Black holes cannot devour everything in the universe simply because the more black hole's "consume" the hotter they get. Eventually the black hole "explodes". This is why black holes will never be able to devour the universe. Also, a black hole cannot become a particle. It is a singularity. A singularity cannot just reverse itself and become a particle. This is why the big bang could not have come from a singularity.

What happens inside the event horizon

I addressed something that I feel needs to be addressed; the fact that whatever happens inside a discontinuity is undefined. Also something to discuss: why can't a moving observer become a discontinuity by moving faster than C? Obviously a black hole can do it to the fabric of space and time with a finite amount of mass, can't we accelerate past the speed of light with a finite amount of energy? What happens when we do? Who knows? It's undefined.--MaizeAndBlue86 (talk) 01:12, 23 February 2008 (UTC)

I undid your edit because it's not correct. In general relativity there's no discontinuity at the event horizon; it's just like any other region of spacetime. The original ideas about wormholes and other universes came from smoothly extending the outside solution past the event horizon, that is, by assuming that the event horizon is the same as anywhere else, which is the opposite of what you wrote. -- BenRG (talk) 12:12, 23 February 2008 (UTC)

My question is, how is a black hole NOT a discontinuity if the wavelength of light is smaller than the smallest thing we can have in this universe (read blue shift). There's a fundamental limit to the blue shift and if you shift past that it's undefined what it is. I'm saying that the region inside the event horizon is an undefined region to the outside world, and inside there could be anything, including another entire universe. In fact, can you say for certain that our universe is not contained within a supermassive black hole? To say that the cosmos only existed for ~13 billion years is very shortsighted, and I don't think it's outside the realm of possibility that our universe is only one that exists 'recursively' within another one, much like other black holes exist within ours. I think you need to redo my edit because there's more insight here than you think —Preceding unsigned comment added by MaizeAndBlue86 (talk • contribs) 16:17, 24 February 2008 (UTC)

The term discontinuity has specific meaning within physics - your statement as it stands is incorrect. Please review outside sources and discuss the ideas here on the talk page before inserting material into the article that you might not fully understand. Also, be sure to include references, particularly when presenting material that may be outside of mainstream. Thanks PhySusie (talk) 19:46, 24 February 2008 (UTC)

Lack of history

There is a severe lack of any discussion of the history of the theory of black holes, the earliest date mentioned in the article is 1917 and references relativity, not black holes - yet I'm reading the May 20, 1905 'Review of Reviews for Australasia right now and sure enough, it's already talking about "inexplicable black holes" as the "most astonishing" part of E.E. Barnard (Yerkes Observatory)'s recent photographs and study of the galaxy. Sherurcij ^{(Speaker for the Dead)} 00:19, 1 March 2008 (UTC)

The black holes referred to in that reference were an entirely different kind of object, apparent ly starless black spots superimposed on the bright Milky Way background. At the time it was supposed that these might be actual holes in the Galaxy where one could look through into the external Universe. Later on, as the size and shape of the Galaxy became better understood, it was realized that such holes would have to be veritable "tunnels" through the field of stars, all pointed directly at the Earth. These dark spots, in their most striking form called "Bok Globules", are now understood to be simply small dense clouds of gas and dust, where new stars are probably forming, and which obscure the stars behind. They have nothing to do with the black holes of this article.

The idea of black holes somewhat similar to our modern concept actually dates back to the 18th century, but that was in the context of Newtonian space, time, and gravity. This actually is discussed in the "Newtonian Theories..." subsection.

Black holes in the meaning of this article really only became conceptually possible with the work of Einstein, whose Special Theory of Relativity (1905) implies that it is a fundamental property of the structure of spacetime that matter, energy, and causal influences can never exceed the speed of light. Einstein's 1915 General Theory of Relativity gave what has become widely accepted as our best current understanding of the correct relativistic theory of gravity, and of the field equations describing it. The first solution of these equations, by Karl Schwarzschild, also gave the first mathematical description of a spherically symmetric black hole. This work really marks the beginning of the understanding of the subject in our current sense of the term, and is described in the history section of the present article.

Cheers, Wwheaton (talk) 07:50, 1 March 2008 (UTC)

Maybe someone should say something about Einstein not believing in black holes, because he knew they couldn't be right. Any time you get infinity in a physics calculation, you know you've done something wrong. Infinite gravitational forces don't exist in physics. REALLY larges onces do, but not infinite.--MaizeAndBlue86 (talk) 13:46, 1 March 2008 (UTC)

Deep question, I think nobody really knows. The $1/r$ in in the gravitational and EM potential energy functions have been there a long time, and we mostly just shrug our shoulders. And string and Big Bang theorists take their models seriously down close to $r=10^{-33}$ cm, which is certainly not infinitely small, but still.... The trouble is that we don't know how to do mathematics unambiguously with infinite numbers, so calculations break down or blow up. But quantum mechanics (and mathematicians too) deal with infinite arithmetic all the time by "subtracting off infinities that cancel", which I think really means going to a limit in the "right" way.

This kind of procedure has worked again and again, and maybe there will be no end to its success, in which case we might have to consider the possibility that maybe Infinity actually is physically real. But mentioning Einstein's unease still sounds reasonable to me, because there seems little ground for extrapolating confidently into the unknown forever. Theories do tend to break down at some point. Wwheaton (talk) 21:49, 1 March 2008 (UTC)

I am familiar with infinities cancelling, but quantum mechanics says there isn't infinitely small. It only gets as small as the planck length, but nobody has ever applied that to black hole theories and that, in my opinion, is a flaw in the theory. Saying that infinity exists and running with it even when we know that it doesn't exist makes physics run around in circles and not go anywhere.--MaizeAndBlue86 (talk) 23:01, 1 March 2008 (UTC)

I think you are right that QM and GR come into conflict at the Planck length, but I believe that only sets a limit on the validity of the theories we have to work with today. I don't think it addresses the deeper question I was trying to get at re. your comment about infinity being forbidden in physics. The successor of our theories today, whatever it may turn out to be, might have some essential finitude built into it, but it seems to me it equally well might not. String theory (I believe) considers its elementary objects, strings or higher-dimensional branes, to have zero extent in some directions in the space they inhabit. If so we might have similar problems at the next level of understanding,..., ad nauseam. I suspect nobody knows if we will ever get to "The Last Level". Gōdel's Incompleteness Theorem gives me no confidence that we ever will, if axiomatic theories are actually relevant to physics. And if no finite consistent theory exists, then I also do not feel confident that there has to be a finite limit on the small or the large. Probably some other editor can make a more definitive statement; I would be most interested if so.

This gets us rather far afield from our topic of black holes, so perhaps we should discuss it further on our own talk pages, if further discussion is desirable. Cheers, Bill Wwheaton (talk) 00:21, 2 March 2008 (UTC)

We can readily point to at least one finite boundary: we know where Absolute Zero is — if for no other reason than that we have established a scale that defines it. Our failures to eliminate "infinity" in other areas of physics may simply be due to our lack of a suitable place to stand. Which is a way of saying that we are probably thinking about these things using concept-labels that don't fit. rowley (talk) 21:08, 5 March 2008 (UTC)

For absolute zero, I always think of ln(kT) as the more relevant physical [?!whatever that means!] parameter, in the sense that decreasing the temperature by yet another factor of ten (or whatever) in low temperature physics seems closer to a step of equal difficulty. And that reminds me that we can always make our infinities "go away" superficially simply by means of a mathematical transformation that regularizes them, as atan(x) maps +/- infinity to +/- pi/2. It is interesting that although I remarked that we cannot do arithmetic with infinite numbers above, the transformation v = tanh(u), where v is velocity (divided by c) and u is "rapidity" maps v (which is not additive, according to the special relativistic formula) into u which is, making infinite u correspond to infinite energy and momentum. Is there a clear criterion for deciding when such a transformation is "physically meaningful", and when it is just numerical smoke and mirrors? I dunno, myself. Wwheaton (talk) 23:25, 5 March 2008 (UTC)

The limit is on our observational methods. We measure things using photons. If we want to know what something looks like we shoot a bunch of photons at it and watch how they bounce off. If you try to do that to something that's smaller than a photon, that's like trying to measure an ant with a bowling ball. The planck length is the distance where measurement with photons breaks down. It's not to mean that nothing exists beneath the planck length, it only means that we can't measure it (using photons) if it does. That's why there is a limit to the infinitesimally small.--MaizeAndBlue86 (talk) 00:27, 6 March 2008 (UTC)

The best way to say what we don't know how to?

Okay, this sentence:

General relativity describes mass as changing the shape of spacetime, and the shape of spacetime as describing how matter moves through space.

...makes slightly less sense than itself. rowley (talk) 20:04, 5 March 2008 (UTC)

Actually that's a well formed sentence, and furthermore, it's true. Can you tell me why it doesn't make sense?--MaizeAndBlue86 (talk) 00:16, 6 March 2008 (UTC)

A case where the sense is all in the definitions, I think. Can we help the "average reader"? Wwheaton (talk) 00:37, 6 March 2008 (UTC)

After reading the paragraph it's not really necessary to the section to talk about space-time curvature when it's simply talking about escape velocity. Maybe just delete and reword the intro?--MaizeAndBlue86 (talk) 01:46, 6 March 2008 (UTC)

Black holes were never detected (just as Dark energy, Dark matter and real scientists)

Why in all these articles on Cosmology everybody claims certainty? We NEVER saw a black hole. Also, as one should be in the center of our Galaxy, it is really disappointing that this FALSIFICATION is given no weight. . Why, also EVERYONE ALWAYS LOVE TO CLAIM that Black Holes complies to General relativity? The infalling mass would EXCEEED the speed of light. Einstein said that, not me. Stop telling tales and start a new wisdom: we PRETEND we know things but we do not. Under this light, most of the scientists are no difference from priests. Show some bravery and rewrote. —Preceding unsigned comment added by 83.103.38.68 (talk) 15:31, 6 March 2008 (UTC)

Actually I'm not so sure that FTL (faster than light) is forbidden. It is only forbidden based on the assumption that our universe is a continuum, which it isn't. How do you explain the fact that our universe is ~15 Bil. years old and ~95 Bil. light years across??? Those numbers say that matter can and does travel FTL.

We haven't observed a black hole or gravastar yet because from the outside it would look very much like any other bright object in the sky. The only thing that would clue you in that it's a black hole/gravastar is if things are orbiting it really fast as if there's a lot of mass inside it. Either that or go there yourself...--MaizeAndBlue86 (talk) 17:00, 6 March 2008 (UTC)

[? I think the two preceding paragraphs belonged together, so I have added a ":" to indent them together.] Of course we do see stars (in the IR and re. the Galactic Center) that have completed nearly full orbits around the center in the past decade or so. That gives us the mass, around 3 million solar masses. But there is still a chink in the argument because one would have to prove that no object (say, 2 million neutron stars, in a cluster a thousand AU in radius) can exist for a reasonable time (that particular case would lose energy due to gravitational radiation and collapse very rapidly). The event horizon for a 3e6 solar mass black hole, with a radius of about 10 million km, would be far to small to see directly, so that "non-observation" does not falsify anything. Wwheaton (talk) 00:01, 7 March 2008 (UTC)

I'm having trouble understanding your argument. Why can't black holes/gravastars exist for a long time? I'm not sure if you are directing your post at me or the other guy.--MaizeAndBlue86 (talk) 02:04, 7 March 2008 (UTC)

I was addressing the other post, by 83.103.38.68, about Galactic Center BH. Point was that we do have significant evidence for a BH at GC, though not quite proof, because we measure mass and see essentially no light. Yet it could still be (logically) something much bigger than a BH (eg, 1000 AU radius, vs 10 million km for BH) with 3 million solar masses, eg, my straw-man cluster of neutron stars. But that is not a very realistic possibility because of short life; and as far as I know, no one has proposed a good alternative other than a BH. Sorry for confusion; hope I did not mangle your earlier post by inserting ":". Wwheaton (talk) 19:05, 7 March 2008 (UTC)

Destroying a Black-Hole

Is it possible, by any means, to destroy a black-hole? I've tought that, if I throw in some (lit) suns inside of it, it could heat it up, and have a smaller density (and bigger size), ceasing to be a black-hole. Is it plausible? Any other ideas? Any theorethically possible way? --Kalel (talk) 18:39, 10 March 2008 (UTC)

Apparently not. Before Hawking's evaporation theory of 1974, we believed that a BH could only grow, never lose mass. The radius of the event horizon (for the spherically symmetric Schwarzschild case) increases linearly with the mass, while the volume of a Euclidean sphere increases as the radius cubed, leading one to the conclusion that the average density decreases as the mass increases. But (I believe) the global properties of the spacetime exterior to the event horizon -- which imply the one-way nature of the horizon itself -- have really nothing to do with the density inside. You could, for example, make a Schwarzschild BH out of a material only as dense as water (or much much less), although the density inside the event horizon would eventually become infinite at the center, subject only to the qualification of our lack of certain knowledge about the result of the conflict between quantum mechanics and general relativity very near the singularity.

I think these general features are unchanged for the rotating and/or charged BH solutions to the Einstein field equations of GR.

Since 1974, it seems likely that BH's do slowly lose mass (and thus energy, of course, per mc²) by thermal radiation, but adding mass will actually lower their temperature, and slow down their rate of mass loss, lengthening their lifetimes. Since there seems no way to remove mass from a black hole except by waiting patiently for it to evaporate, there seems no way to hurry the process and "destroy" a BH, pending further theoretical enlightenment. Wwheaton (talk) 02:18, 11 March 2008 (UTC)

Yes, and certainly if there was a way to destroy a BH, feeding it more mass is not it. That's how it got to be a black hole in the first place! Besides, a lot of BH has millions-billions of solar masses; what is one more sun when you've got a billion of them already? It won't make a difference.--MaizeAndBlue86 (talk) 10:38, 11 March 2008 (UTC)

As a black hole "eats" more the hotter it becomes. By constantly feeding a black hole matter it will eventually explode because of increased temperature. This is what I have read in a book called Black Holes, A Travelers Guide. It is an excellent explination of black holes. However I have also read up on Hawking Radiation. Will someone please clarify which one or if both are correct.11341134a (talk) 18:52, 12 March 2008 (UTC)

No, that's not correct. Adding matter to a black hole makes it colder—the Hawking temperature is inversely proportional to the mass. You can extract energy from a rotating black hole by gravity assist (see Penrose process) and I think you can increase the rate of Hawking radiation from a charged black hole by dumping in opposite charges to neutralize it, but other than that you have to wait for it to evaporate (which can take a long time). -- BenRG (talk) 21:08, 12 March 2008 (UTC)

Yes, that is my understanding also (except I don't know anything about the effect of charge on the rate). I think that "Travelers Guide" is just incorrect, at least on that issue. Wwheaton (talk) 21:34, 12 March 2008 (UTC)

Yeah, I dispute the adding charge to increase the rate of radiation bit. Hawking Radiation does not come about because the black hole is charged, it is entirely due to the presence of an "event horizon", which has nothing to do with charge. I put 'event horizon' in quotes, because I think the classical notion of an event horizon as described by this article is wrong and has been perverted by black hole theory, but that's a different topic entirely.--MaizeAndBlue86 (talk) 22:25, 12 March 2008 (UTC)

Modelling Hawking radiation as a manifestation of Unruh radiation does not require an event horizon. --Michael C. Price ^talk 22:36, 12 March 2008 (UTC)

The Other Side of a Black Hole

After hearing a few theories on what might've happen'd prior to the Big Bang recently, I got to wondering about Black Holes. Does anyone have any thoughts on what happens to all of the matter/mass/energy that is sucked into a black hole? Where does it go? Please, I know my question is very simple, but I ask it nonetheless. I'd like to hear your thoughts on this. Bix12 (talk) 09:06, 12 March 2008 (UTC)

There's an interesting hypothesis on this very thing if you read the gravastar page. This is an attempt to fix the black hole theory, partly because nobody can explain what happens to all that mass inside a black hole. Inside a gravastar, which is very similar to a BH, there is an explanation:

Basically, gravastars hypothesize that all the matter implodes "through" the center and "explodes" out into another dimension, and expands indefinitely. Hmm...kind of sounds like the big bang dont you think? That's what gravastars hypothesize, that our universe was in-fact a massive explosion as a result of a gravastar forming, and we are inside it! --MaizeAndBlue86 (talk) 12:37, 12 March 2008 (UTC)

The baseline notion, which is not very satisfactory to many, has been that the mass/energy just sits there in a point singularity, of finite mass but zero size. This appears to be in conflict with quantum mechanics (QM), which is very well established for sizes down to well below the size of an atom, but not extending to the 10^-33 cm sizes where the problems between QM and general relativity (GR) become acute. String theory and its relatives are the best attempts to date at reconciling QM and GR, but remain work in progress.

There are also some theoretical indications that the strongly curved spacetime in the immediate neighborhood of the singularity connects to flat (ie, uncurved, Euclidean) spacetimes that are not connected to the region immediately external to the black hole. Whether these connections ("wormholes") are to distant regions of our own universe, or to other universes, and whether it is possible for mass, energy, or information to pass through them into (or from) the other spacetimes has been controversial for a long time, and remains unclear so far as I know, so this possibility may or may not be relevant to the issue. Wwheaton (talk) 15:01, 12 March 2008 (UTC)

The mass dropped into a black hole goes nowhere - the hole simply gets more massive, like any other object in universe that accretes. You don't need to worry about the central singularity to understand this. Think of it from the Ruskie frozen star POV; the singularity never forms; all the infalling matter is frozen in time and never reaches the centre. --Michael C. Price ^talk 08:16, 13 March 2008 (UTC)

It's frozen in time from the POV of the outside observer, but inside it still has its own proper time. Mass goes somewhere because it's conserved; black holes don't make new mass. How can you be satisfied with saying that it "goes nowhere"? It most definitely goes somewhere, and that's why black hole theory is incomplete.--MaizeAndBlue86 (talk) 10:32, 13 March 2008 (UTC)

but inside it still has its own proper time. no, because "inside" would take place after the black hole has evaporated, i.e. the mass hangs around ("goes nowhere") until it is eventually emitted in the Hawking radiation.--Michael C. Price ^talk 10:38, 13 March 2008 (UTC)

So you're saying that when the mass actually reaches the "singularity" it is emitted as hawking radiation instead of going somewhere else? Wouldn't that imply a simply enormous luminocity; converting 100% of all the mass it accretes into radiation energy?

Secondly, I saw you have a Masters degree in Quantum field theory. So how can you accept the notion of a infinitesimally sized singularity? That's a General Relativity thing that doesn't coincide with the accepted existence of a 'smallest size', according to quantum theory.--MaizeAndBlue86 (talk) 15:15, 13 March 2008 (UTC)

You misunderstand. There is no singularity in the frozen star model. The star never collapses through its event horizon (the latter which remains an entirely mythical or classical concept which is not realised in the quantum universe due to Hawking radiation).--Michael C. Price ^talk 15:46, 13 March 2008 (UTC)

Thus if I understand you are saying that the singularity never really happens, because a distant observer never sees anything actually fall through the event horizon. Even though the proper time of the observer falling in is finite (and quite short), he never reaches the event horizon either (not even in his own time), nor the "mythical singularity", but is converted to Hawking/Unruh radiation and emitted, in a short time according to his free-falling clocks? I will have to think about this a bit. I had never heard of Unruh radiation until a day ago, although I have (sort-of) understood the "event horizon" that seems to occur in special relativity, for a uniformly accelerated observer, for a long time. This seems possibly related to User:MaizeAndBlue86's gravastar, which I have not really understood either.

My impression is that this is not appropriate for the article at this point, so maybe we should continue the discussion on our talk pages? But I am very interested, and thanks. Cheers, Bill Wwheaton (talk) 15:38, 13 March 2008 (UTC)

Hi Wwheaton, yes you have understood what I was saying. I think the frozen star model is an appropriate topic for this article since it was the original model for black holes -- and one which has resurfaced again recently. --Michael C. Price ^talk 15:46, 13 March 2008 (UTC)

This is what I was thinking of:New Scientist story questioning the reality of event horizons --Michael C. Price ^talk 17:21, 13 March 2008 (UTC)

I saw that too, and was very interested, but did not carry its implications far enough. Since the proper time of the infalling astronaut before passing thru the event horizon of a BH (a "mature", pre-existing one, that is) is short, it never occurred to me. Still a lot to think about here! Bill Wwheaton (talk) 22:53, 13 March 2008 (UTC)

Yeah that does sound like a gravastar to me. To the outside observer, all the matter towards the center appears like Bose-Einstein condensate; extremely red-shifted (and cold!) and super-imposed on all the other matter inside. But to an observer inside the condensate, it would not look like that at all. It could conceivably be a whole new universe inside.--MaizeAndBlue86 (talk) 16:06, 13 March 2008 (UTC)

Gravastars don't sound like frozen stars to me. The latter makes no assumptions about BECs etc.--Michael C. Price ^talk 17:09, 13 March 2008 (UTC)

I think it does though. You're talking about a LOT of mass kind of "suspended" in a perpetual free-fall towards the center. All of that mass together in a compressed space-time would appear like a superposition of their wavefunctions to the observer at infinity. Hence the Gravitational-BEC.--MaizeAndBlue86 (talk) 17:26, 13 March 2008 (UTC)

Except that as time contracts space expands in the Schwarzschild metric, so there is no compression. --Michael C. Price ^talk 17:39, 13 March 2008 (UTC)

I don't understand what you mean by this. The metric distance to the event horizon is finite; there's not unlimited room there. Also, I don't see how Hawking radiation is related to the question of whether infalling matter really crosses the event horizon. Hawking's original paper includes a conformal diagram that looks like this:

            |\
            | \
            |  \
        ____|   \
       |   /   /
       |A /   /
       | / B /
       |/   /
       |   /
       |  /
       | /
       |/

where A is the interior, B is the exterior, the vertical lines are timelike r = 0, and the horizontal line is the singularity. In this picture the infalling matter does pass through the event horizon and hit the singularity. The reason you get the same amount of radiation out as matter fell in is that the metric is asymptotically flat and therefore there's a well-defined total mass which has to be conserved. It isn't actually the same matter. I'm aware that people disagree with this picture, but they seem to be in the minority right now. Certainly the naive picture of a frozen star is wrong; you have to come up with a model that explains in detail what happens to the infalling matter (i.e. by what physical process it turns into Hawking radiation, if that's indeed what it does). -- BenRG (talk) 19:30, 13 March 2008 (UTC)

The infalling matter is accelerating relative to the external fixed observer (the time dilation is counterbalanced by the space expansion). So the mechanism is simply Bremsstrahlung = Unruh effect = Hawking radiation. I'll have to come back on the metric distance issue with a detailed calculation, but the point about how Hawking radiation stops a particle crossing the event horizon is easy -- mass is being lost with the escape of radiation therefore the horizon (if it exists) is retreating from the external observer and vanishes in finite external time: pretty much as is implied by the New Scientist link I gave above. Essentially the back reaction has to be included in the conformal diagram and I'm not sure that it is.--Michael C. Price ^talk 23:10, 13 March 2008 (UTC)

This appears to be nothing more than wishful thinking. You need a mechanism for the conversion of the infalling matter into radiation. It has to turn completely into radiation, violating various conservation laws in the process, and it has to do this despite not knowing that it's falling into a black hole, because according to GTR there's no way for it to know. You can't just wave your hands and claim it works. It doesn't work in GTR. If you're committed to the frozen-star idea then you're going to have to give up on general relativity and find a replacement that predicts what you want it to predict.

With a metric of $ds^{2}=(1-2m/r)dt^{2}-(1-2m/r)^{-1}dr^{2}\,\!$ the distance from $r_{0}$ to the horizon at constant t is $\int _{2m}^{r_{0}}(1-2m/r)^{-1/2}dr=r_{0}{\sqrt {1-{\frac {2m}{r_{0}}}}}+m\log \left[{\frac {r_{0}}{2m}}\left(1+{\sqrt {1-{\frac {2m}{r_{0}}}}}\right)\right]$, which is finite. -- BenRG (talk) 00:28, 21 March 2008 (UTC)

I'm talking about from the viewpoint of an observer at infinity. There most definitely is a space-time compression according to him. You're right about inside though, the matter will not see the compression. But an observer in flat space-time has limits to what they can observe. Everything they try to observe inside the "frozen star" will be a big red-shifted blob. Maybe in your description it would be a fermionic condensate, and not a bosonic condensate, but the principle is the same.--MaizeAndBlue86 (talk) 17:58, 13 March 2008 (UTC)

It's meaningless to say that there is spacetime compression according to an observer at infinity. An observer at infinity is just that: someone making physical measurements very far from the hole. They have no instrumentation near the hole which could serve to establish a coordinate system there. -- BenRG (talk) 19:30, 13 March 2008 (UTC)

Disagreed. It is very meaningful to relate something according to an observer at infinity, because once you establish rules for this observer, they direct you to establish rules for observers closer to the BH/GS/FS. I mean, according to BH theory the gravitational field around the singulariy goes asymptotically, so no matter how close you get to it, there's an infinite amount of space in between you and the singularity, so you might as well be observing from infinity.

Also, special and general relativity are only tools with which to translate data sets from one observer to another. If an observer at infinity measures something, you can use equations to translate that to another observer, say, close to a gravastar. Physics is entirely about observers and events.--MaizeAndBlue86 (talk) 21:05, 13 March 2008 (UTC)

No, everything you've just said is untrue. The metric distance to the singularity is finite. The tidal force goes to infinity, not the distance. I don't know what you mean by "rules" for an observer, but you don't get one set of measurements from another set of measurements, you get both sets from the underlying spacetime model. The word "observer" is used in two totally different ways in relativity. In only one of the two senses can you mathematically transform between the "observations" of different "observers", and that sense has virtually nothing to do with the usual colloquial English meanings of those words (hence my scare quotes). That sense of "observer" is rarely used in general relativity. I don't think it should be used in special relativity either, as it's incredibly misleading. Don't make the mistake of thinking that the Lorentz transformations of special relativity can be extended to observers in general relativity; it's a totally different situation. As far as I'm concerned there's never a good reason to use the word "observer" in any discussion of 20th-century physics. It can always be more productively replaced by a description of the actual measurement apparatus involved—for example a video camera or an inertial reference frame (which is a particular kind of measurement apparatus made of clocks and metersticks arranged in a certain way). -- BenRG (talk) 00:28, 21 March 2008 (UTC)

I don't know how to respond to that, except to say that what you've said is untrue. Any time you specify position or motion or acceleration you always say it with reference to the observer. By itself, motion is meaningless. It is motion relative to another thing that matters - one observer's perception of another. If you're in a high gravitational field, space and time look normal to you; it's the same size and duration to you. The only difference it makes is relative to other observers, not in the same space-time curvature you are. I think the Newtonian view of an "absolute universe" was abandoned long ago. The "universe" is defined by the observer.--MaizeAndBlue86 (talk) 01:46, 21 March 2008 (UTC)

Question on Black Hole Physics

If nothing, not even light can escape a black hole than how do graviton waves escape the black hole to act on other objects? Also I have heard a lot about exotic matter that would make a black hole a stable wormhole. If this matter even exists it has a negative charge. Thus would it not be repelled by gravity? How would one even get it to the black hole without the matter being repelled by the black hole's gravity?11341134a (talk) 18:31, 12 March 2008 (UTC)

Don't confuse waves with fields. A wave is a kind of field, but not all fields are waves. The field of a black hole is not a wave or a collection of waves, it's a static equilibrium configuration. Gravitons, if they exist, would be waves; a static field would not be made of gravitons. Maaaybe it would be "made of virtual gravitons", but virtual particles don't follow the usual rules of causality, so (a) they're not stopped by event horizons and (b) they don't make much physical sense anyway.

In general relativity the field of a black hole stays there because there's nothing else for it to do. Fields are local, so any change would have to come from somewhere, and it can't come from inside the hole because of the event horizon. So once the field has settled into an equilibrium state, it doesn't change any more.

Negative mass would gravitate just like ordinary mass according to the equivalence principle, i.e. it would be attracted toward a black hole. But being attracted isn't any better than being repelled; what you need is something that will keep it in just the right place, and there's no known physics that will do that. General relativity lets you take any geometry and work out a corresponding distribution of energy. That doesn't mean that every geometry makes sense, because for most of them you'll get a energy distribution that can't arise from any plausible physical laws. So the existence of stable wormhole and warp drive solutions doesn't really mean anything. The energy distributions don't look reasonable, not only because of the negative mass but because there's nothing to force it to be where it needs to be. -- BenRG (talk) 20:02, 13 March 2008 (UTC)

BOLD STATEMENTS! "[Virtual particles are] not stopped by event horizons and ... they don't make much physical sense anyway". Virtual particles are stopped by the "event horizon" according to Stephen Hawking: that's where Hawking Radiation comes from; two virtual photons not being able to annihilate each other because one got taken by the "event horizon". The presence of virtual particles also accounts for various other physical anomalies that I can point you to in my Quantum Mechanics textbook if you want.

Also, maybe you should review your quantum mechanics textbook--> EVERYTHING is a wave, including light, including atoms and also including your "gravitational fields"; All of space and time that we can presently observe is made of photons (also waves).--MaizeAndBlue86 (talk) 21:17, 13 March 2008 (UTC)

black holes are still to be proved

But as I read the article it's so hard to understand that we still have no definitive proof. And the so called scientific consensum cannot be used to mask the fact that in this encyclopedian voice there is a lack of doubt. That's not correct.83.103.38.68 (talk) 16:36, 19 March 2008 (UTC)

Do you disagree that astronomers have found evidence like gravitational pulls, jets, and ect that could not have been caused by anything else than a black hole? What do you think happens to massive stars like say Beteguese when they collapes? Do you deny that they collapse into BH? P.S. I am extremely sorry about the harsh comments I made before... I was angered at something that happened that day and I should not have come into wikipedia with that mindset. I am sorry. I beg your apologies. Begging your forgiveness, 11341134a (talk) 00:30, 20 March 2008 (UTC)

All the astronomical data tells us is that there exist very dense objects which show very little other signature then being very dense. For some of these objects we can pretty much rule out that they are some sort of neutron stars. The only thing left that they could be are black holes. But this could just be problem with our understanding of physics at those scales. General relativity could break down in such a way that an horizon never forms. We don't know. The astronomical data most certainly doesn't give us any conformation of the characteristic features that would define it to be black hole. There is no (in)direct evidence of an event horizon either in the form of Hawking radiation or in the form arbitrary large redshift. (TimothyRias (talk) 09:23, 20 March 2008 (UTC))

It is important to appreciate also that the existence of black holes is not dependent on what happens in super-strong gravitational fields or extreme spacetime curvature, nor of the properties of matter at very high densities. For example, a ball of normal water 10¹⁰ km in radius (roughly twice the size of the Solar System) would have a mass of around 2 trillion solar masses, and a Schwarzschild radius of ~6 trillion km, though its density would be (for a little while) just 1 gm/cm² throughout. But since it would be inside its own event horizon, the gravity of such a large mass in such a small region, would produce a spacetime curvature external to the matter sufficient to create that event horizon, independent of the microphysical properties of the matter inside. The event horizon is a global property of the spacetime external to it, and that does not seem to depend on the extrapolation of physics to unexplored regimes. An even more extreme case would have occurred if we had lived in an expanding universe with an average density larger than the "critical density" of the cosmological models of a decade or two ago. This would have made a "closed universe", which would eventually stop expanding due to its own gravity, and re-collapse, apparently into a future singularity. In this case we would actually be living now inside the event horizon of a black hole, falling into the inevitable disaster, even though we might not reach it for billions of years, and would not notice anything amiss from observations of the local universe. (Cosmology has advanced since then so that it seems we are not destined for that particular doom.) Cheers, Wwheaton (talk) 00:03, 21 March 2008 (UTC)

Mistake about singularity and relativity.

"While general relativity describes a black hole as a region of empty space with a pointlike singularity at...". Well relativity cannot have sinlularity points. I hope someone will correct it. I won't.19:03, 19 March 2008 (UTC)83.103.38.68 (talk) 16:38, 19 March 2008 (UTC)

This sentence you quote is in the third paragraph of the Introduction, and is qualified after your "..." ellipsis; the first sentence of the (current) introduction gives our definition based on our understanding of the exterior spacetime, which is all we can approach observationally. While we have to admit that our understanding of the region inside the event horizon is surely incomplete, yet the definition in terms of the exterior region, based on observations to date and on the best theories we have available, seems to be correct, regardless of whether there is really a singularity at the center. The statement to the effect that relativity cannot have singularity points may well be true, but I think it is not really established. I believe the definition of black holes does not depend on its truth or falsehood. Best regards, Wwheaton (talk) 19:49, 19 March 2008 (UTC)

I'll second that more strongly: according to all non-quantum physical theories a singularity of zero volume and infinite density is inevitable since the forces that collapse a mass beyond the density of a neutron star have overcome neutron degeneracy pressure, the strongest of the forces that resist compression - so the stars that form black holes go on collapsing to zero volume because nothing can stop them and it's a vicious circle - the smaller the radius of a given mass, the larger its surface gravity pulling on itself. Quantum mechanics does not allow masses of zero volume, and one of the biggest issues in physics for the last nearly 90 years has been how to reconcile quantum mechanics and general relativity, both of which are accurate in their own domains (the extremely small and the extremely large respectively). Philcha (talk) 20:11, 19 March 2008 (UTC)