Talk:Black hole/Archive 8

More vandalism

Someone put a brief reference to the phrase "black hole" being a "derogatory term" in the opening sentence. This is most likely referring to the debacle in Dallas County TX regarding a county commissioner and judge treating the phrase as some kind of racist remark.

Irishchieftain (talk) 16:50, 11 July 2008 (UTC)

Would it be complete without a mention of that incident? In other words, should that incident have a mention in this article? Pop6 (talk) 18:09, 12 July 2008 (UTC)

I would say, no--if later, a significant number of physicists abandoned the term in favor of another as a result of the incident, then it could be added at that time. Right now, it seems there is no likely effect on black hole research and the story will be nothing more than an anecdote.--Todd (talk) 18:43, 12 July 2008 (UTC)

Understood. Makes sense. Pop6 (talk) 17:13, 13 July 2008 (UTC)

Broken Link

Please replace http://www.hubblesite.org/go/blackholes with http://hubblesite.org/explore_astronomy/black_holes/home.html —Preceding unsigned comment added by 12.30.36.40 (talk) 19:54, 3 April 2008 (UTC)

Fixed. Thanks for pointing it out, but please feel free to correct any such deadlinks yourself in the future! - Parejkoj (talk) 00:19, 4 April 2008 (UTC)

Splitting up the article

The Black Hole article is way too long and covers way too much ground on its own. I think it should be spilt into a number of sub-articles. Do other people agree? Much of the information covered in the article is already covered by other more specalized articles.

Some sub-articles could be: - Observation of black holes. (covering pretty much everyhting about astronomical observations of black holes, including stuff about accretion discs.) - Evolution of Black Holes (covering formation and possible evaporation of black holes.) - Maybe a section about the history of blackholes. - Other suggestions? (TimothyRias (talk) 10:58, 26 March 2008 (UTC))

sugestion blackholes acoording to: einstein physics, quantum physics, string theory, information theory. Most of those theories (and perhaps more) have contributed to the science about it.(but dont askme to write it it's above my level) his might be written in a historical time frame way. Meaning year : idea (link to another wiki page) The best way might so be lots of stub articles to get all the info it. Perhaps for the previously named topics (by TimothyRias) as same per year view could be made. —Preceding unsigned comment added by 82.217.143.153 (talk) 01:33, 27 March 2008 (UTC)

I think this should only be done very carefully, after some discussion and hopefully consensus here about the major sections and the scope of each. Personally, I think a basic overview article should at least outline the major results from the general theory; the range of possible types (micro to super-massive, Schwarzschild (ie, non-rotating spherical), Kerr (rotating), and charged, with major qualitative differences pointed up; briefly summarize observational evidence in hand and those likely yet to come (eg, terminal gamma-ray flashes from evaporating small BHs; GR waves from forming or coalescing BHs from neutron stars or previously existing BHs). There should also be some mention of the (controversial) question of wormholes and Hawking radiation. Probably each of the major sections should be brief, giving only the highlights of results from current understanding, and link out to more extensive articles with more detailed explanations and more references.

If such a split is deemed a good idea at all (I am undecided, myself), perhaps the way to start would be with a strawman outline? Then we could haggle over that for a while.

Bill Wwheaton (talk) 19:16, 27 March 2008 (UTC)

A further topic that should at least be mentioned, I think without technical detail, would be the conflict between quantum mechanics and general relativity, possibly to be resolved by string theory, but not yet completely understood. Wwheaton (talk) 21:07, 30 March 2008 (UTC)

I have been looking at it more carefully, and I think a lot can be achieved by simple editing and to the appropiate sub-articles when needed. Here are some proposals:

• Sections 1,3,4,8 are all concerned with various aspects concerning classification of BH's (no hair, size, charge, etc.) These could be merged into a single section covering classification of black holes.
• Section 6 about major features of rotating black holes belongs in Rotating black holes with appropriate links from here.
• Section 13 about the dangers of BH's is pretty much pointless and should be removed. (part of it could be moved to micro black holes.
• The advanced topics section (15) should be summarized to basically just links to the advanced topics themselves.
• Section 16 about the mathematical theory of schwarzschild BH's can be missed in the overview article. (there should be good links)

• There either needs to be a good section linking to all the other black hole articles. Or we needed a navigation template for the BH topics. (to be place on each black hole page.

(TimothyRias (talk) 22:18, 1 April 2008 (UTC))

For easy reference I have compiled a list of all Black hole related articles that I could find on my user page. This might be useful when deciding to move parts of this article to other more specialized articles. Feel free to notify me of other related articles you might find on my talk page. Thanks(TimothyRias (talk) 12:47, 2 April 2008 (UTC))

A nav template would be excellent. Re the rest, I'd be happy to split out "Techniques for finding black holes", "Black hole candidates", "History of the black hole concept", "Alternative models", " More advanced topics" and "Mathematical theory of non-rotating, uncharged black holes" provided they are linked to in sub-sections of the remaining "Black Hole" article that summarize them.

I'd still want to keep "Black holes and Earth" because refuting popular misconceptions is a useful function of Wikipedia (if it was good enough for John Locke to be an "under-labourer" clearing away the obstacles, it's good enough for Wikipedia).

I think the rest of the content should remain in at least a simple form, to make clear to non-specialist readers the full scope of the subject. For example I'd be happy to move the Penrose diagram that's currenntly in "Possibility of escaping from a rotating black hole" but would still want to see at least a coherent summary of rotating BHs.

Since we'd be turning BH into something of a portal article, we should consider a "BHs in popular culture" section - there may be enough uses in science fiction books alone to fill a page; and there are many derivative uses of the term. Philcha (talk) 11:35, 12 April 2008 (UTC)

OK, I've made a temporary page with a proposal for a new version here. I've merged many of the sections and referred a lot to info that is already on other pages. My editing has been pretty aggresive in some cases. So somethings should be readded or integrated that are now missing. But at least we are back to 6 main section with some resemblance of structure. Any comments?

While editing I also noticed that the current version contains an old version that has been completely commented out. It can be found here. (TimothyRias (talk) 13:48, 14 April 2008 (UTC))

Re the old version that was commented out, well spotted. It's my fault, when I restructured the article in spring 2007 I kept the commented out stuff in order to mine it, and forgot to remove it.

Re your User:TimothyRias/temp proposed new version:

• I agree revision is needed. I've just looked at the article for the first time in several months, and there have been some changes that I'm not happy with. The first one that struck me was "Black hole parameters", a mathematically-oriented section that will put off non-specialist readers. If it's accurate it should be in a seperate article with the other more technical stuff.
• I'm not happy that your version starts with "Classification", for the same reason that I don't like to see paleontology articles give a lot of space to "Classification" too early: it does nothing for the non-specialist reader. OK, the current version starts with grouping by size, but its aim is simply to explain the sizes of BHs, not to set up a taxonomy. As a fairly hard-line empiricist I prefer to see and present the facts first. Hence I'd prefer to keep "Black hole parameters and the "no hair theorem"" and "Types of black holes" in their current position. The 2nd para of "Types of black holes" (charged BHs unlikely in reality) needs to be rewritten - 1 sentence has commas in all the wrong places but its fundamental defect is that it's too long and complex.
• I think the 2nd section should be "What makes it impossible to escape from black holes?" (currently the 3rd section), because the impossibility of escape is the defining feature.
• I think the article needs to distinguish clearly between features of non-rotating and rotating BHs. Failure to do so will not just confuse non-specialist readers, it may also give ammuninition to Wikipedia's critics. But it would be nice if we can find ways of making these 2 sections shorter in total.
• Personally I like your shorter decription of "Event horizon", but I'm fairly familiar with the concepts. I still think non-specialist readers need the introductory paragraph - and Hawking or his editor obviously thought the same. I'm less sure about the sentence "... the light is moving away from the black hole at the rate of c, but the spacetime is being sucked into the black hole at the same rate ..." because: it uses the shorthand c without explaining it, and explaining it would just complicate matters; "... the spacetime is being sucked into the black hole at the same rate ..." will confuse non-specialist readers who are still getting their heads round the concepts, and may be inaccurate - AFAIK spacetime is not sucked in, it's bent more severely as one gets closer to the centre.
• Hawking radiation is not a feature of black holes, it's a theory about the ultimate fate of BHs. I still think it's better as part of a section about the lifecyle of BHs ("Formation and evaporation"). The Hawking radiation theory is also based on quantum mechanics, and I think this should wait until most of the features of the General Relativity model of BHs have been explained - once again to avoid confusing non-specialist readers.
• The section "Evaporation of larger black holes" (within "Formation and evaporation") should be removed: it's in the wrong place, and evaporation is dealt with in reasonable detail a little further down).
• In "Evaporation of larger black holes" the sentence "The Heisenberg uncertainty principle dictates that it is impossible to know the exact value of the mass-energy and position pairings" assumes far too much prior knowledge. This is not your fault, it's in the current version of the article. The sentence was added sometime around mid-2007 as someone's attempt to explain fluctuations in the quantum vacuum (for example the version as at 03:02, 5 April 2007 does not have this sentence), but I think it introduces more complications than it resolves. I also think that the current version's reference to "fluctuation (thermodynamics)" complicates matters, and I don't know if it's correct. Philcha (talk) 15:57, 14 April 2008 (UTC)

I agree, mostly. My editing up till now has many focussed on recombining some of the smaller sections that tended to overlap a lot.

• There should be a better first section. Maybe, the current what happens if you fall in a black hole section can be editted to serve as a proper introduction. Is should probably also include the information that is currently in the why can't escape from a black hole section. The section introduces many features of a black hole in a mostly none technical way.
• Classification is probably a bit of a misnomer for the section with that name. It mostly deals with introducing the different types of black holes discussed in the article. In doing so it also provides linkage to the more technical articles. I feel this should stay early in the article.
• I don't see any good reason to distinguish between rotating and non-rotating black holes. Physically, they aren't that different. The Schwarzschild solution is just a special case of the Kerr-Newman solution. Generically, all black holes should thought of as rotating, with the rotation is some cases being negligible. I think the article should thus deal with properties of black holes in general. When a certain remark applies to specific situation this should be noted. When writing an article about star you also would distinguish between rotating and non-rotating stars?
• About the event horizon. I removed the Hawking reference for several reasons. For one an encyclopedia should not reference popular scientific works such as a brief history of time. It makes an article look amateurish. (As if the authors had no better source than that.) Moreover, I do not find Hawking's remarks that helpful and in some cases misleading.
• I disagree about your remark about Hawking radiation. Hawking radiation is a feature of black holes. (or more correctly a feature of event horizons.) Its effect on the evolution of a black hole is a different matter (and much more subject of debate.) Hawking radiation actually says very little about the ultimate fate of black holes, because its clear that the derivation leading to it, breaks down long before a black hole could evaporate.

Also feel free to do some editing in the proposal I made. It can probably use some reorganizing, but at least it groups the information in the current article together in more coherent sections. (TimothyRias (talk) 07:08, 15 April 2008 (UTC))

I think before discussing any more details we should be clear about the differences in our perspectives.I see from your user page that you're a competent mathematician and physicist, which I would not claim to be. Although your knowledge of the subject is much greater than mine, you are at risk of assuming that others start with a similar level of knowledge (at least within an order of magnitude). I don't think we can assume such a level of prior knowledge in non-specialist readers. Specialists don't consult Wikipedia on subjects related to their own speciality. So IMO the article should be as intelligible as possible for people who have not done any maths or physics since leaving school.

Now for details:

• I'd like to move "What makes it impossible to escape from black holes?" up so it's the first section heading. That would make the point that even the most powerful spaceship can't escape, and would also prepare non-specialist readers for just how wierd BHs are compared with anything in their normal experience.
• As a result "Sizes of black holes" would immediately precede "No hair theorem" and "Types of black holes". This would have the effect of your proposed "Classification" section, but I prefer to avoid a single section called "Classification": the heading says nothing to non-specialist readers; and it might tempt future editors into producing a more detailed taxonomy of BHs. Detailed taxonomies early in articles are more likely to deter non-specialist readers than to enlighten them; they should follow the explanation of what an X is (see Mammal for an example of more detailed taxonomy in the right place).
• I agree that in practice BHs are likely to rotate (0 angular velocity is a very special case). But I think we should first explain non-rotating BHs, as rotating BHs have additional features such as ergospheres and annular singularities with possible "wormholes". After all it took physicists 30 years longer to produce a solution for rotating BHs than for non-rotating BHs. From your point of view non-rotating BHs are just a special case, and it's easier for you to remember just the 1 set of equations for rotating BHs and plug in a zero value if you ever want to calculate something for non-rotating BHs. but non-specialist readers don't know those equations and wouldn't understand them.
• "What happens when something falls into a black hole?" should follow the descriptions of non-rotating and rotating BHs, because it uses ideas explained in these sections.
• The current mathematical section "Black hole parameters" should be moved to the same place as the more technical content currently at the end of the article. It also contains one small inaccuracy at the beginning, since it omits charge as a theoretical property of BHs (although highly-charged BHs are physically very unlikely).
• Re "Event horizon", I now agree that Hawking's comments should be removed: the part about police is just silly, and without it "the point of which light is just barely able to escape" explains nothing. I also think the words "but at the same time, light does not get sucked into the black hole" should be removed. We do need a description of what happens to light that approaches on a path tangential to the event horizon. Can you provide one?
• Your comment "Hawking radiation actually says very little about the ultimate fate of black holes ..." is interesting - can you please explain why it does not imply that BHs will completely vanish. At present I still feel that for non-specialist readers the natural place for it is at the end of "Formation", but I'm willing to learn why that might not be best.
• So we also need to re-examine "... the cosmic microwave background radiation becomes weaker. Eventually it will be weak enough so that more Hawking radiation will be emitted than the energy of the background radiation being absorbed by the black hole ..." at the end of the current "Evaporation" section.
• Going back to your suggestions at the very start of this discusion, I think the best chance of reducing the size of Black Hole is to split off some of the topics. I'm not sure about "Alternative models" and suspect black Hole should make it clear that there are alternative models. But I'd be happy to see:
  • the observational material ("Techniques for finding black holes" and "Black hole candidates") as 1 article (it's about 25% the size of the current version of Black Hole).
  • "History of the black hole concept" as another (just over 1 screen of content on my monitor, so at least it wouldn't be a stub).
  • "More advanced topics", "Mathematical theory of non-rotating, uncharged black holes" and "Black hole parameters (currently section 8), but I don't know enough of the theory or maths to judge how to package them. Also the last paragraph of "Mathematical theory of non-rotating, uncharged black holes" contains some information that could be prsented in non-technical trms in Black Hole, possibly under the heading "vital statistics". Philcha (talk) 12:34, 15 April 2008 (UTC)

(reset indent) (on yout point about perspective. I agree the article should be intelligible to people with little prior knowledge. However, we should realize that at a lot of people reading this will have enough prior knowledge to see through the most naive statements. Hence it is important to at least refer to a proper argument when trying to stay intelligible. Moreover, it is my believe that blatant lies never helped anybody. I spend a lot of time explaining black holes to people at parties (occupational hazard) and a lot of that time is often spend is correcting the damage done by well intend but fundamentally wrong popular accounts.)

• It is probably a good idea to make the "what makes it impossible to escape from a black hole" section to the front.
• The three sections that follow the this (sizes, no hair, types) should be merged to single coherent section explaining the basic properties of black holes. (mass, charge and angular momentum). This should probably not be called classification for the reasons you noted. But it is necessary since we will need concepts like mass, charge and angular momentum.
• On the topic of rotating and non-rotating black holes. I believe we should just explain black holes. Most general features hold for all black holes. (All have event horizons, photon spheres and singularities.) Stuff like the singularity of a stationary black hole being a point is not that important (and not a general feature.) It is however useful as an illustration. Ergospheres, could be discussed as well, as long as it is noted that this feature only becomes important when the rotation is large. (on a side note, accretion discs should note be mentioned when discussing features of black holes. They are not a general feature of black holes. They aren't even unique to black holes.)
• The "Black hole parameters" section doesn't really added anything in my opinion. The one thing that we made should take from this, is that the other parameter section needs some order of magnitude indications for the sizes of black holes. (i.e. a stellar mass black hole is about the size of a large city etc.)
• I think we agree on the "event horizon part". (I'll try to come back on the issue of photon hitting the horizon tangentially. I'm not sure that this even possible. UPDATE: I checked, it is not possible for a lightray/nullgeodesic to hit the horizon tangentially. In fact, null geodesics coming in from infinity can only become tangent to the the horizon outside of the photon sphere.)
• The discussion about Hawking radiation would be a lengthy one. But, basically it boils down to the fact that the derivation of the hawking effect assumes the black hole to be large. It is not clear if a hole would keep radiating when it gets small. If not then one could end up with so called remnants. (But the discussion goes deeper than that. It is not even apparent that hawking radiation should in fact cause a BH to lose mass, altough the current concensus is that it probably would.) The gist of my point was that the effect as such would be one that comes hand in hand with the appearance of an horizon. As such it is a feature of a BH. I think it should be mentioned when discussing feature. Later in the "evolution" part it should be mentioned that this effect could cause the evaporation of a BH over time.

(TimothyRias (talk) 09:15, 16 April 2008 (UTC))

I think we now agree on just about all important points. My main reservation is about combining the descriptions of non-rotating and rotating BHs, but we can see how that works out as the article develops.

Many thanks for your patience. Philcha (talk) 13:18, 16 April 2008 (UTC)

I've implemented some of the ideas discussed. I have used comments to remove some of the sections that needed to be removed but may contain some information that deserves a place elsewhere in the article (TimothyRias (talk) 08:59, 18 April 2008 (UTC))

blackholes and string theorie

a beginner level movie about blackholes and physic theories :movie about blackholes from harvard, easy to understand, it might be handy as a background for people totaly new to this subject. just wished to share it here. —Preceding unsigned comment added by 82.217.143.153 (talk) 21:43, 27 March 2008 (UTC)

Very nice film about the interface between General Relativity and Quantum Mechanics, which I recommend to interested non-experts, like me. Most relevant to string theory as a possible resolution of the conflict. A couple of reservations:

• his first slide might mislead a newcomer into thinking the BH property depends on mass alone (he gives escape velocity for Moon, Earth, and BH), but of course it also depends on the size of the object (as does strictly classical escape velocity) -- eg, if the Earth could be squeezed into something smaller than a cherry, it would form a BH;
• I am in doubt about his "nothing nothing" statement, as I have understood that in an old-fashioned (ie, pre-1995 or so) closed universe, our observed universe would all be "inside" a black hole, that is, between the event horizon and the inevitable future singularity, which would be far from "Nothing".

Bill Wwheaton (talk) 21:02, 30 March 2008 (UTC)

Accretion Disk question

I noticed that the section Accretion Disk is a sub-heading of the section "Major features of non-rotating, uncharged black holes". My question is: how could a non-rotating black hole have an accretion disk? Wouldn't the accretion disk add to the black hole's angular momentum as matter fell in? Also, it seems like any supernova that resulted in a black hole with an accretion disk would require the black hole to be rotating in the same direction as the accretion disk. If I am correct, then the accretion disk section should be moved under "Major features of rotating black holes"

Jpmerrill1 (talk) 15:06, 2 April 2008 (UTC)

I'd say it actually belongs in the observing black holes part. Accretion discs aren't features of black holes per se. You can have black holes without accretion discs. Accretion discs are merely a useful phenomenon that with the observation of compact objects such as black holes. (TimothyRias (talk) 20:07, 2 April 2008 (UTC))

If I remember correctly the Accretion Disk is an area of space were objects that rotate the black hole move faster because of the black hole's gavety(sp?). Any black hole could have a Accretion Disk. I also think that TimothyRias is corect and th info would be better under observing black holes since the disk is only shown when an object gets close to the black hole.3rd captian Gin Ichimaru (talk) 10:55, 10 August 2008 (UTC)

Vandalism as first line

Someone posted vandalism as the first line in this article, stating that someone "sucks at Halo 3" —Preceding unsigned comment added by Conxion528 (talk • contribs) 19:59, 7 April 2008 (UTC)

As an object passes through the event horizon...

As it stands right now, the article states that the Earth could be passing through an event horizon without us ever noticing. Please help me understand how this can be. If the earth were near an event horizon (let's say a supermassive black hole), wouldn't half of our sky be obscured by the giant blackness? Doesn't it stand to reason that, since we're able to see stars in every direction, we're not close to an event horizon? I understand that passing through the horizon is nothing extraordinary, but wouldn't we know that we're passing through it by not being able to see in the direction of our freefall? Dmitry Brant (talk) 19:19, 8 April 2008 (UTC)

I will take a crack at this, though my understanding is imperfect, and maybe someone else can come along and do a better job. Event horizons seem to have something to do with the global geometry of a spacetime. For the case of an event horizon surrounding a black hole, you are probably right. But there are other situations that seem to produce event horizons that are somewhat different. Consider for example an observer A accelerated in a straight line at a uniform rate in his own local frame. In a Minkowski diagram his world-line would then be a hyperbola tangent to the time axis (ie, vertical) at the origin, O, but with an asymptote tangent to the world line of a light signal proceeding at 45 degrees to the upper right, intersecting the original vertical time axis at some future point P. (Never mind that, from an engineering point of view, he would need an incredible super-rocket to stay on this hyperbola.)

This person's (A) experience, in his own frame and proper time, would be just as if he were in a constant and uniform gravitational field, but he would see an unaccelerated observer B left behind at O, more and more red-shifted, until that observer B 's clocks seemed to stop, in the sense that his time would never get beyond that point P where the 45-degree asymptote intersects the original time axis. No matter how powerful a rocket B might have, he could never catch A if he started the chase after that moment P when A sees his clock stop (the perfect get-away!)

This situation "smells" very much like a gravitational event horizon, and if we consider the Equivalence principle of general relativity, that acceleration and gravitation are essentially similar, then I think it is hard to avoid the conclusion that they must be really the same sort of phenomena. In particular, if we think of B as falling in the equivalent G field, he passes through an event horizon, from which he can never escape. Yet obviously B notices nothing remarkable as he passes P, as he is just sitting there at rest innocently minding his own business.

No doubt this argument will not answer your question completely, but I hope it helps. Wwheaton (talk) 00:23, 9 April 2008 (UTC)

That helps a bit, thanks; But by that reasoning, are you saying that there exist reference frames where an observer wouldn't realize that he's inside a black hole? Dmitry Brant (talk) 03:17, 9 April 2008 (UTC)

Wwheaton's explanation is pretty accurate (at least for so far you can go with relatively simple arguments). And yes this means that there are frames were an observer would not realize he was in a black hole. Well, at first for a very big black hole, inevitably as he will approach the singularity he will feel ever bigger tidal forces, which will be hard to ignore. Moreover, in a finite amount of time (on his own clock) the observer in the black hole would hit the singularity which also can't be a pleasant experience. (TimothyRias (talk) 07:35, 9 April 2008 (UTC))

Well, I understand that we may not feel tidal forces until much closer to the singularity, but wouldn't there at least be some strange optical effects when approaching/crossing an event horizon (such as not being able to see in the direction of the singularity, redshifting of the stars behind us, etc)? Or am I interpreting that incorrectly? It just seems that the idea of "not noticing" crossing the horizon is extremely counter-intuitive.

Perhaps it would be useful to add to the article a 360-degree panoramic description of what an in-falling observer sees a) right before crossing the horizon, b) as the horizon is crossed, and c) past the horizon. This might help more "visual" people like myself to understand these perplexing effects. Dmitry Brant (talk) 15:57, 9 April 2008 (UTC)

I suspect that cannot be done in a general way, as it seems to depend heavily on the external boundary conditions rather than just the local situation at the observer. These are different for a BH than for the peculiar "modified special relativistic" example I gave above. Note that the infalling Cosmic Microwave BG would be blue-shifted to higher and higher T for an observer approaching a BH event horizon, but would come from a smaller and smaller disk overhead -- in the limit it seems to me it would look more and more like a very hot and bright star. It seems that the interior region would have to look black, though there is the puzzling caveat that we can never really see into it because it is infinitely red-shifted and fades out (as does my understanding...!) There have been attempts to portray what an observer approaching a BH would see (IIRC ? on the cover of Physics Today a few years ago?) but I am not sure I quite trust them to have everything accounted for at the boundaries. Wwheaton (talk) 18:04, 9 April 2008 (UTC)

Dmitry Brant asked, "If the earth were near an event horizon (let's say a supermassive black hole), wouldn't half of our sky be obscured by the giant blackness?" The centre of the black hole has zero dimensions (ignoring quantum mechanics) or sub-microsopic dimensions (according to quantum mechanics), so it would not block the view. That leaves the question of by how much light appears to be bent for an observer just inside the event horizon, and whether light from objects on the far side of the BH (black hole) would be bent enough for them to be invisible, creating the effect of a "black disk" masking them. I'm no expert on the maths, but the Schwarzschild radius (radius of the event horizon) is directly proportional to the BH's mass. That implies that supermassive BHs are much less dramatic than minimum-mass BHs (about 2.5 solar masses). I don't know all the equations, but I think fairly simple logic indicates that an observer just inside the event horizon of a supermassive BH would not see anything very unusual. AFAIK conditions just (infinitesimally) inside the event horizon are the same for small and supermassive BHs (provided the observer is compact enough not to be affected by spaghettification in the case of a small BH); and so are conditions at the centre (total annihilation). That implies that conditions change much more rapidly as one moves towards the centre of a small BH than when moving at the same speed towards the centre of a large BH. So I would expect light-distorting effects to become noticeable very quickly in the case of a small BH and very slowly for a supermassive BH. In the case of a supermassive BH and an observer just inside the event horizon, the central "black disk" would appear very small, about the apparent size of the Sun viewed from Pluto; and the disk within which light-distorting effects such as gravitational lensing become obvious might be much less tha the radius of the event horizon. Of course things are different for an observer crossing the event horizon: outside the event horizon objects on the far side of the BH are invisible because the light from them is trapped by the event horizon; so when the huge black disk becomes transparent you know you've crossed the event horizon and are doomed (but might still have a reasonable life expectancy if the BH is mega-supermassive and its radius is therefore larger than our solar system, if you follow the slowest possible spiral towards the centre). Philcha (talk) 11:11, 15 April 2008 (UTC)

Micro Black Hole Creation Mechanics

I Question the statement in the article:

"However, many particle collisions that naturally occur as the cosmic rays hit the edge of our atmosphere are often far more energetic than any collisions created by man. If micro black holes can be created by current or next-generation particle accelerators, they have probably been created by cosmic rays every day throughout most of Earth's history, i.e. for billions of years, evidently without earth-destroying effects."

The creation of micro black holes may require very precise mechanics to focus all energy to a single point. Mechanics may required same mass, same speed, exact head-on vector of two particles colliding precisely center mass. This may be an expected scenario for a percentage of collisions in a head-on particle accelerator, but may be nearly unprecedented in nature. --Jtankers (talk) 07:43, 14 April 2008 (UTC)

The expected collisions are physically the same. The cosmic ray <-> atmosphere collisions will be head on and center of mass in some frame. The only real diffrence is that in a collider the center of mass frame will coincide with the approximate rest frame of the people doing the experiment. (Which implies that low velocity BH's may be created.) But the argument that nothing unprecedented in nature will happen, still holds. If you want to worry about unprecedented physics is expermints, go look at Bose-Einstein condensation. Now, there you have unprecedented physics. (This experiments create physical circumstances which to our knowledge have never occured in nature in the history of the universe. But, I haven't heard anybody complain about those experiments. (TimothyRias (talk) 10:09, 14 April 2008 (UTC))

Just added spaces & ":" to format previous comments to clarify signing. Wwheaton (talk) 12:38, 14 April 2008 (UTC)

Intro

I changed the end of the 2nd para of the intro to "leaving all matter and radiation with nowhere else to go" because AFAIK that's more accurate. See for example the Schwarzschild explanation of "What makes it impossible to escape from black holes". Philcha (talk) 08:35, 15 April 2008 (UTC)

What makes it impossible to escape from black holes?

I've edited this in an attempt to make it easier for non-specialists to understand:

• escape velocity applies to unpowered objects, including light.
• BHs also trap even the most powerful spaceship - no amount of energy is enough to enable escape.
• attempt to explain why different co-ordinate systems are necessary, with a simple analogy. I know the analogy is incomplete, because it assumes observers on both sides of the lens use Cartesian co-ordinates. If anyone can supply a more generalised one that's still intelligbible to non-specialist readers, please edit it in.
• commented out the bit about light cones because it has a fairly obvious flaw as stated in the article - at any non-zero distance on the time axis, a light cone normally presents a non-zero cross-section area, i.e. various places to which one can go. The web page cited (Schwarzschild's Spacetime: Introducing the Black Hole) avoids this problem by showing light cones narrowing as the observer gets closer, but does not explain why. I suspect that explaining this point would just complicate the account without providing any additional benefit to non-specialist readers. If the light cone has zero cross-section area at the time co-ordinate represented by the free-fall time to the centre (so it's not a cone any more, it's a spindle), that represents the time axis pointing towards the centre of the BH, as already described by the Schwarzschild coordinates. If the centre of the BH fills the cross-section area, despite having zero dimensions (ignoring quantum mechanics for the moment), this would require further explanation of how the BH distorts spacetime. Philcha (talk) 10:11, 15 April 2008 (UTC)

I would avoid mentioning coordinate systems altogether. Coordinates in general just confuse and in this case are probably unnecessary, since the used concepts work fine in a coordinate free context.

Also in my experience talking about escape velocities in the context of black holes just confuses people. The argument is just too flawed, and people tend to pick on the flaw fairly easily. Which is usuallu followed by utter confusion.

I also think you are missing the point about light cone tilting. (Note that the lightcone is actually a subset of the tangentspace at a point. Hence it is always a cone!) On the other hand in don't think that the lightcone tilting argument will do anything for people who don't know about lightcones. The best argument to use I think is that spacetime deforms in such a way, that time is pointing into the black hole. This argument is fairly correct and is very close to what is actually happening. It also connects to a simple fact that everybody knows, namely that you cannot move backwards in time. (So, the short answer to the question: "Why can you not escape from a black hole?" would be: "because you cannot move backwards in time. (TimothyRias (talk) 14:49, 15 April 2008 (UTC))

I'm quite happy to drop all mention of lightcones. And I agree that, if we're going for only "time flows towards the centre", we should skip the confusing stuff about coordinate systems. Thanks for confirming that it's a sensible approach.

The reason I left escape velocity in and actually tried to explain a bit more is that I've seen popular accounts that rely on the concept of escape velocity, and of course they fail to explain why a powered object can't escape (dont' ask me for citations!); I certainly remember a few people posting questions to archived versions of this Talk page that assumed an approach based on escape velocity. A reader who's seen such an account will not be satisified unless we show that the escape velocity explanation is at best incomplete. Do you know a better way of dealing with this? Philcha (talk) 16:27, 15 April 2008 (UTC)

I agree, it might be sensible to include some mention of the escape velocity argument, just because it is commonly used in popular accounts. If we do, we must also point out the flaws in the argument. (it is not apparent why have an escape velocity equal to c would imply that light is trapped.) We could probably, start the section with somethong along the line: "In popular accounts black holes are often explained by calculating the escape velocity of a dense object..." The continue to point out the flaws in the argument. This would be followed by an explaination of how black holes can be understood as deforming space in such a way that "time is pointing inward". Ideally this should be a compainied by a qualitative picture. (Such a picture would probably look a lot like the ones you see in lightcone tilting arguments. After all, the lightcone tilting argument is just a technical way of saying that time is point inwards in the black hole. (TimothyRias (talk) 08:17, 16 April 2008 (UTC))

I've done a rewrite of the section to reflect what we discussed above. Probably still needs some editing/shaving. It definately needs some kind of pictorial illustration. I'll try to work on that when I have time. (TimothyRias (talk) 14:16, 18 April 2008 (UTC))

The section is very "talky" and should be made more encyclopedic. The way it sits now is what I would expect in a lecture, not in a encylopedia or text on the matter. Mikemill (talk) 14:34, 18 April 2008 (UTC)

I've added an illustration. The captions can probably use some more work, but should help visualize what the section is trying to say. (TimothyRias (talk) 17:07, 27 April 2008 (UTC))

I like the pictures, but light cones don't "really" tilt like that, it's specific to the Eddington-Finkelstein coordinates. (At least, those look like Eddington-Finkelstein light cones.) In terms of intrinsic geometry the inside of a Schwarzschild black hole is spatially homogeneous much like the FLRW geometry, so there's really no direction you can go that takes you closer or farther from the horizon. Your statement above that "spacetime deforms in such a way that time is pointing into the black hole" sounds 100% right to me, but I'm worried that this illustration of it is somewhat misleading. In terms of the symmetries of the manifold time points "straight in", not at an angle. -- BenRG (talk) 20:05, 27 April 2008 (UTC)

I know. I purposefully made the pictures extremely qualitative avoiding the mentioning of any type of coordinates, or light cones for that matter. It would only cloud the point being with a whole lot of technical discussion. Of course, if you would like to you could always find coordinates in which the light cones behave exactly as in the picture. I purposefully avoided having paths that seemingly move 'backwards in time', or 'faster than the speed of light' to avoid raising unnecessary complicating questions with a less informed reader. (TimothyRias (talk) 20:38, 27 April 2008 (UTC))

Okay, I can live with that. -- BenRG (talk) 21:16, 27 April 2008 (UTC)

Why not add link to the English translation of SCHWARZSCHILD SOLUTION? See below.

http://xxx.lanl.gov/abs/physics/9905030 —Preceding unsigned comment added by 69.37.168.74 (talk) 16:51, 19 May 2008 (UTC)

Edits to 1st sentence and Spaghettification section

I made many minor edits and two not-so-minor edits. First, I changed some "which"s to "that"s. And, second, (and on the not-so-minor side) I added a few words to the first sentence of the article, clarifiying the extreme nature of a black hole's gravitational pull. I also added some clarification to the section, Spaghettification. There, I described spaghettification in slighlty more detail, explaining the bifurcation process (i.e. spaghettification) that bodies undergo when they fall inward to the singularity. Hope these changes are OK with everyone... Cheers, ask123 (talk) 21:17, 17 April 2008 (UTC)

Made some more changes to the first paragraph. They are too many to detail here; so please check the edit history if you would like to see them. ask123 (talk) 22:00, 17 April 2008 (UTC)

You may also want to replace "halves" with "pieces" in that section. There is no reason the expect the object will be teared into exactly equal halves.

Yes, you are right. If it hasn't been changed already, I will do so. ask123 (talk) 14:10, 5 May 2008 (UTC)

merged size, types and no hair sections

I merged (and partly rewrote) the "types of black hole", "sizes" and "no hair" sections to single section dealing with the properties of black holes. (TimothyRias (talk) 14:35, 21 April 2008 (UTC))

Features sections

I'd like to see the two sections "Major features of ..." merged to a single section. I feel that currently there is too much emphasis on rotating en non-rotating objects being different. Globally, they are not that different at all. I think it would be better to have a single section called "Features" first discussing the general features a black hole has: Event Horizon, Singularity, Photon sphere, and discussing the major new feature introduced when rotation comes into play, the ergosphere. I don't think we should mule over stuff like the exact shape of the singularity (and there being multiple horizons for charged and rotating black holes. Those are more technical issues, better dealt with in their respective articles. On the same note, I think the part about the possibility of escape from a rotating black hole should go. Properly explain this is way to technical, and if include this we should also include other features introduced when "extending" the space time such as white holes and Einstein-Rosen bridges for Schwarzschild black holes. And I don't think that would be desirable. (TimothyRias (talk) 09:12, 23 April 2008 (UTC))

Did so. Probably still needs some work. Time for some merciless editing. (TimothyRias (talk) 14:10, 7 May 2008 (UTC))

Event Horizon

I'm not sure if this was mentioned, as I couldn't read the entire article due to length, but in an Astronomy class I took, the instructor told us about a theoreum that stated: Once inside the event horizon, moving away from the singularity will actually speed up the desccent, as will moving in any other direction. Just thought it was worth mentioning. —Preceding unsigned comment added by 69.249.20.210 (talk) 22:18, 23 April 2008 (UTC)

Put it in if you can find a website that supports your claim; a.k.a., cite it. From what I know, that's correct. But there are better people to ask. IceUnshattered (talk) 22:52, 29 May 2008 (UTC)

This article -- "No Way Back" seems to say that different rates of outward acceleration have different effects. See Figure 2 on Page 3. More comments here -- "Universe Today" --Harry Wertmuller HarryWertM (talk) 23:29, 10 June 2008 (UTC)

As I understand it, "moving away from the singularity" is as impossible as it is impossible for you to move in the direction of yesterday. I have drawn a crude picture here: http://busybox.net/~vda/blackhole_1d.png . Inside event horizon, the direction "to the center of the hole" is the direction of _time_ coordinate axis (as perceived by falling observer - the "big" coordinate axes in the picture is coordinate system as seen by distant observer). For the falling object, the center of the hole lies in all possible object's futures. It can't avoid coming there, just like you can't avoid arriving into tomorrow. VZ9 (talk) 16:22, 29 June 2008 (UTC)

Swartzchild Singularity

Note: Black Holes may also be known as Swartzchild Singularities, so that could be the title for a page to help sort out the length of this article. Just a suggestion, please don't curse me out. 69.249.20.210 (talk) 22:23, 23 April 2008 (UTC)

Note: it is Schwartzschild. It is pronounced schwartz-schild, not schwartzs-child as some americans like to rape it. (Some of them notable theorists too!) (TimothyRias (talk) 12:03, 24 April 2008 (UTC))

Nothing worth swearing about! It is actually spelled "Schwarzschild" -- no "t", though the German "z" is pronounced like "tz".

But the term singularity properly refers only to the place where a mathematical expression blows up (typically because a denominator in a formula becomes 0). The term "black hole" refers to the whole horrendous kablooie, or at least everything interior to the singular surfaces (eg, event horizon). The "Schwarzschild singularity" is properly just the singularity at the Schwarzschild radius, a hollow spherical shell, and is a bit of a mathematical fiction (though it does have physical implications: you can't go home again), in the sense that an observer falling in would not necessarily notice anything weird happening to his local space, he would just feel more or less stretched by tidal forces, depending on the mass. There is a real physical singularity at the center, where the physics blows up somehow, subject to our uncertainty about quantum mechanical effects. But the black hole is bigger than just that, and it is hypothesized that we can never actually see it in there, anyhow. Wwheaton (talk) 01:37, 4 May 2008 (UTC)

Black hole types

The recent edit of "Black hole types" does not mention that BHs with significant charge are not expected in nature - was there something wrong with this statement? Without it, some readers will be puzzled that the article does not say anything further about charged BHs. Philcha (talk) 13:15, 24 April 2008 (UTC)

Actually, it is mentioned in the first sentence of the subsection following it, sizes.

Under natural conditions black holes are expected to form with negligible charge and small angular momentum. Hence the Schwarzschild solution is a good approximation for most black holes.

I did remove some of the hand waving that went into explaining why this is, though. (TimothyRias (talk) 13:32, 24 April 2008 (UTC))

The "small angular momentum" statement is questionable, is it not? As for normal matter, charged black holes result in strong, long-range forces tending to neutralize them. No such neutralizing forces come into play for angular momentum, although there is a limit to how much they can have. I think fast rotating, nearly "extremal", BHs are viable possibilities in reality, just as there are stars and asteroids that rotate close to breakup speed. My information may be outmoded. Am I mistaken about this? Wwheaton (talk) 15:25, 25 April 2008 (UTC)

MTW (RIP W) says "Most objects (massive stars; galactic nuclei; ...) that can collapse to form black holes have so much angular momentum that the holes they produce should be 'very live' (a nearly equal to M; S nearly equal to M²)" (Box 33.3, page 885). That is, it says that most black holes should be near-extremal (but uncharged, of course). This isn't exactly a recent source, but I thought I should throw it out there since it directly contradicts what's currently in the article. -- BenRG (talk) 19:02, 27 April 2008 (UTC)

The statement seems to be a little over the top. Needs correction. (TimothyRias (talk) 19:23, 27 April 2008 (UTC))

OK, based on the above I'm going to moderate that statement and leave the angular momentum issue open. I do not recall having ever heard that extreme Kerr solutions are unphysical in an astronomy context, though I could certainly have failed to notice. Bill Wwheaton (talk) 21:47, 27 April 2008 (UTC)

I found an ApJ ref from within the past year or so that determines the rotation parameter a>0.98 for GRS 1915+105, so I have expunged the claim of small angular momentum, redone the third paragraph of the "Black hole types" subsection and the first paragraph of the following "Sizes" subsection. I am inexperienced and clumsy about wikimath, so if anyone can make the math look better, that would be nice. But mainly read over it and make sure it makes sense. Wwheaton (talk) 00:54, 28 April 2008 (UTC)

I fixed some of the wikimath stuff. Since you are mentioning extremal black holes, I think we might want to devote a paragraph to introducing the fact that there is a maximal charge/angular momentum given a certain mass. (TimothyRias (talk) 08:11, 28 April 2008 (UTC))

done (TimothyRias (talk) 12:45, 28 April 2008 (UTC))

Timothy, apologies, but I reverted that for the moment, as there were some things I think were incorrect. Here are your two original paragraphs:

While the mass of a black hole can take any value, both the values of the charge and the angular momentum are constrained. This is due to the fact that charge and angular momentum add to the energy to an object and thus add to the mass. Consequently, a black hole formed out of such objects must have a mass large enough to accommodate for the charge and angular momentum going in to the black hole while forming. A black hole that has the maximum amount of charge or angular momentum (i.e. a black hole consisting purely out of electromagnetic or rotational energy) is called an extremal black hole. Extremal black holes have special properties, making them important in the study of quantum gravity and supersymmetry.

Because the universe is mostly electrically neutral, black holes are expected to form with negligible mass. However, since astrophysical objects tend to have angular momentum, black holes formed in nature tend to rotate. The black-hole candidate binary X-ray source GRS 1915+105 even appears to have an angular momentum near the maximum allowed value.

I am dubious about the sentence "Consequently, a black hole formed out of such objects must have a mass large enough to accommodate for the charge and angular momentum going in to the black hole while forming", especially. I do think also noting the extremal charge  issue is a good idea, except that I don't know anything about it. In the second paragraph, the first sentence is incorrect, a typo maybe; did you mean "charge"instead of "mass"? But even then the reason is not that the universe is nearly neutral, but that huge electric forces come into play that cause strongly charged bodies to attract charges of the opposite sign, and thus be be quickly neutralized. Of course this can only happen if there are opposite charges available, but it is the strong electric force that makes it happen.

I can't work on this at the moment, but I think we need to work out a different wording before doing the article. The original version from yesterday was wrong about the angular momentum being small, if you want to revert what I did and go back to that point, but just change that error (which needs to be done quickly in the light of McClintock et al 2006 & GRS 1915+105), then go ahead. Wwheaton (talk) 17:20, 28 April 2008 (UTC)

Everything TimothyRias wrote looks right to me, except for the typo you noted. The hypothesis that a black hole with q² + a² > m² can't exist is cosmic censorship, and there are plenty of reasons to think it's true. Qualitatively speaking a very rapidly rotating object will spin itself apart instead of collapsing and a very highly charged object will push itself apart instead of collapsing. Re the second paragraph, it's true that if the universe had a net charge density we wouldn't expect black holes to be neutral. Black holes are expected to be neutral because (a) the universe is neutral overall and (b) electromagnetism acts to homogenize the charge density (in contrast to gravity's effect on mass). Either of these alone is telling half of the story, so maybe both should be mentioned. -- BenRG (talk) 19:01, 28 April 2008 (UTC)

I have no problem with saying q² + a² ≤ m², my problem is with the suggestion that mass somehow makes "room" in the BH to hold the charge and angular momentum. Maybe the sentence can just be reworded. But I had not encountered the concept of an extremal BH as composed of Q and/or J without other mass; have to think about that a bit. (I've probably learned something there.) As far as the other issue, I know that if a gram of hydrogen were separated into electrons and protons, and the two placed at opposite poles of the Earth, the electric attraction would be many (hundreds of, I think) tons. Forces of that order do not come up to enforce cancellation of J, which is what I was getting at. Wwheaton (talk) 21:22, 28 April 2008 (UTC)

Oops, with regard to the obvious typo. With regard to charge and angular momentum taking up "room" in the mass: the phrasing might be a bit akward, but the argument is not that hard. It takes work to bunch up mass and/or angular momentum this work is build up as potential energy, which contributes to T₀₀ component of the stress energy tensor and hence to the mass. Normally the gravitational effect of this energy would be negligible, but in extreme cases the gravitational pull of this potential energy can become enough to cancel the natural repulsion of charge. In the case of an extremal black hole this potential energy is the only contributer to the mass of the black hole. For charge this is pretty straight forward to see, the angular momentum case is very similar though. This is indeed an example of cosmic censorship, but in this case it can be shown without resorting this conjecture (which is known to fail in certain cases!)

Regarding black holes forming with very little charge. In my view, this mainly because the form from objects that were already neutral. Of course, this has to do with the fact the electromagnetic force is strong. Although arguably the fact that opposite charges attract is more important than the actual strength. Anyway, in the case of black holes we are not in a regime were the statement the EM-force is much stronger than gravity is obviously true. As I just discussed in the case of extremal black holes they can become of the same magnitude. Anyway, the neutrality of the universe is enough to explain the small charge expected in black holes. (TimothyRias (talk) 08:35, 29 April 2008 (UTC))

OK, suppose we just say that the J & Q of a BH of a given mass M, are limited according to the q² + a² ≤ m² relation (if we renounce natural units in this article, per discussion below, we have to write out the extra factors needed to specify q  and a  of course)? I think we might do well to present this constraint as a requirement of the theory, and discuss it more thoroughly later in the article, or possibly externally, maybe in the rotating black holes article, which is kind of a mess at the moment, but could be made nice as a systematic discussion of the whole issue, since the present article is bulging at the seams already.

I do think my position on the charge is more nearly correct, again because (as with angular momentum), in the absence of large electric forces (which are surely much stronger than gravity in astrophysical pre-BH formation scenarios), there would be no reason why some objects should not have a large excess charge of one sign or the other, even if the total net charge in the universe was nearly zero. However, we can sidestep that issue and be non-committal on that particular in the article until we have better consensus here. How does this sound? Best, Bill Wwheaton (talk) 17:23, 30 April 2008 (UTC)

I've done some work on this section, essentially not addressing the above issues about charge and angular momentum, thinking the q² + a² ≤ m² relation should really be dealt with later, or in a more specialized article, probably the one on Rotating black holes, and hoping the section introduction is OK otherwise. It seems to me that the far-field for all three cases must converge to the Kerr form (with a reduced mass), and that in turn goes over to the Schwarzschild form for large r. If this is right, it might be worth mentioning. I did fuss with the wording a bit, and I also tried to tighten up the definitions of the size classes, and improve the connection with their origins. Others may want to confirm or revert some areas where I am fuzzy, as eg. the upper mass limit for formation out of a single star, and the largest stellar-mass case presently well established. I believe Cygnus X-1 is already too big to have formed from a neutron star binary, so except for the possibility of formation from a cluster  of neutron stars, I think the likely cases and formation modes are fairly well covered. Anyhow, please check it over. B Wwheaton (talk) 01:06, 4 May 2008 (UTC)

I did some reworking on the micro black hole part. After a couple of edits it had lost most of its structure.

Also, indeed, for large r (compared to the schwarzschild radius) rotating and charged BHs will resemble the schwarzschild metric. Even for a maximal BH if r is bigger than say 10 times the schwarzschild radius, the corrections for charge and rotation already become minor. (a matter of a couple of percent.) (TimothyRias (talk) 10:53, 5 May 2008 (UTC))

I added a table giving an indication of the order of magnitude of the various sizes of black holes. This should help to give a reader an intuition for how big/small these things are. —Preceding unsigned comment added by TimothyRias (talk • contribs) 13:39, 6 May 2008 (UTC)

Black holes in popular culture

I would like to have seen something about this, perhaps as part of a separate article. It interests me that we find the idea of BH so appealing. The public never seemed to need the physics to believe that such things could exist (however misconceived). Even if it were possible now to prove that they don't exist (which seems unlikely) I think the concept would live on in the popular mind, like Atlantis. Do you think there could be a place for a brief discussion of some of the films and books that have featured BH? Kilmahog (talk) 23:01, 24 April 2008 (UTC)

Some kind of myth vs. science section, perhaps. For example, as a child, I was fascinated by the Black Hole from Walt Disney. Explaining to people that the black hole is not a hole, nor a kind of multicolored vortex could be interesting, I guess. People get a lot of badly conceived ideas about BHs, and ignore that the scientific truth is somehow as awing as legends/myths. Paercebal (talk) 13:01, 25 April 2008 (UTC)

Let me tell you what a black hole is. It is a pure spirit. Not a ghost. Spirit matter. It has no time or space. It is a vaccum. It sucks in what is near it because , matter is an illusion, it can make it or create it. You can not identify the element that creates everything in the universe. It expands and diminishes because it can create or destroy. It is what made the universe when there was none. Just as scientist cannot explain the phenomenon of ghost, much less can they explain the phenomenon of a black hole, which does not contain material baggage as a ghost, and is more pure than the common spirit with past life baggage. —Preceding unsigned comment added by 76.237.14.105 (talk) 08:54, 25 April 2008 (UTC)

You must be kidding? Paercebal (talk) 13:01, 25 April 2008 (UTC)

In the sciences we assume, postulate, an external reality that we can investigate by reason, based on observation. We push that assumption as hard as we can, and see how far it gets us. I think the success of the program has been considerable, although I suspect the hypothesis cannot be finally, rigorously, proved or refuted. But those of us following this path will not give it up easily, as it has brought us so far. Wwheaton (talk) 14:57, 25 April 2008 (UTC)

Capitalization of the Sun and other proper names in astronomy

I think it is generally accepted within the astronomical community, and recommended by the IAU, that the Sun, the Moon, and the Earth be capitalized, being proper names. I am not sure if there is a Wiki standard on this subject. Non-proper usages (eg, "a galaxy consisting of billions of suns", "planets may have moons", "a wall made of earth", etc) should be lower case. I just changed "sun" to "Sun" everywhere I found it in the article accordingly. Wwheaton (talk) 06:29, 28 April 2008 (UTC)

Your interpretation is correct, per the MoS, here..."when referring to specific celestial bodies (our Sun, Earth and Moon).". It really should have been handled that way from the start; good catch. Doc Tropics 07:40, 28 April 2008 (UTC)

19th century

In the history section they mention the theories of the 1700s and that interest didn't pick up until the 19th century, then it tells us about the theories of the 1900s, the 20th century. Is this a mistake by the editor(writing 19th century for 1900s) or do we simply not have any information? —Preceding unsigned comment added by Kaloo (talk • contribs) 18:08, 7 May 2008 (UTC)

Is it possible to destroy a black hole?

Is it possible to destroy a black hole? It would be interesting to note in the article. --XUniverse (talk) 01:50, 13 May 2008 (UTC)

You could maybe destroy a Black hole with anti-matter? --XUniverse (talk) 01:54, 13 May 2008 (UTC)

No, not through any process currently known to physics. (Except maybe passively through Hawking radiation) (TimothyRias (talk) 08:16, 13 May 2008 (UTC))

The only known ways for a black hole to be destroyed is for it to evaporate, or to be eaten by another black hole.3rd captian Gin Ichimaru (talk) 10:45, 11 August 2008 (UTC)

Black Holes & Proton Decay

The article on the heat death of the universe states that near the "end of time" "Effectively, all matter would be contained within black holes, which are immune to proton decay, and leptons." Why is matter inside of a black hole immune to proton decay? Neither this article nor that one properly addresses it. --JD79 (talk) 02:43, 13 May 2008 (UTC)

I guess that they are referring to the conclusion that once particles have reached the singularity they pretty much seize to exist as a particle and are just absorbed into the singularity if you will. This since you cannot speak of a proton sitting at the singularity. Hence since there are no protons in the singularity they can also not decay. But any such statement is sketchy at best, since protons are intrinsically quantum mechanical objects and QM doesn't really make any sense near the singularity. So, I usually refrain from such statements. The statement in heat death of the universe might need some clarification on this matter, but I do not think it should be treated here. (TimothyRias (talk) 08:24, 13 May 2008 (UTC))

It's kind of an interesting question, my first thought was that the statement in the heat death article was just unwarranted. "Heat death" refers to coming to a final state of maximum entropy, where everything is in thermal equilibrium, ie, at the same temperature. I believe the original idea was basically that. But now we understand that a self-gravitating system can never reach a final state of thermal equilibrium, because its potential energy is unbounded below. This is especially clear in the case of globular clusters, which look like a gas of stars at first glance, but can never reach thermal equilibrium. Again, it seems the Universe was essentially in thermal equilibrium early in the Big Bang, but gravitational clumping intervened and caused structure to form -- again via the effect of negative gravitational potential energy. I guess I think it is not really understood. Wwheaton (talk) 02:09, 29 May 2008 (UTC)

The point remains that in all probability protons would not be a stable solution inside a black hole, so proton decay just isn't a proper concept inside a black hole. (TimothyRias (talk) 14:49, 29 May 2008 (UTC))

Formation and evaporation section (new section)

Here are some proposals for the formation and evaporation section.

• Currently, the section discusses the formation on the basis of the sizes of black holes identified earlier in the article. As such it repeats a lot of what has been said there. It might be a little more useful to format this section according to the different processes. (i.e. stellar collapse, growth through accretion, sponatneous creation in high energy processes, evaporation.)
• I think a better title would be formation and evolution.
• I propose the following structure:
  • start with a small 1 paragraph intro followed by several sections:

1. Stellar collapse: includes most of the information in the current formation of stellar mass BHs section. Thus: collapse of stars to compact objects, TOV limit, formation of BH from other compact object after sufficient accretion of matter. Covers production of stellar mass black holes and the formation of intermediate mass BHs from hypernova.
2. spontaneous production (needs better section title): The production of BHs in various high energy process. Should at least include inflation (=production of primordial BHs in big bang, special case of Hawking radiation from cosmic horizon!) and creation in high energy collisions (cosmic rays, LHC). This section covers formation of primoridial/micro BHs.
3. Growth: Covers the growth of BHs through accretion of matter/merger. Should cover the formation supermassive BHs.
4. Evaporation. Covers possible evaporation of BHs through Hawking radiation. Should mention the time scales involved.

Is this a workable scheme? (TimothyRias (talk) 09:55, 13 May 2008 (UTC))

I have made start with this at User:TimothyRias/temp. The text there is still very rough and needs checking on factual correctness. (Some of it is just coming straight from my memory, and may not yet be very precise.) The quality of the prose also leaves to be desired. Feel free to make contributions there. I will replace the current section with the one developed there when it reaches an acceptable mature stage. (TimothyRias (talk) 10:08, 15 May 2008 (UTC))

I have improved the draft version on my user page. I will probably replace the current section with that one in the next few days.(TimothyRias (talk) 13:43, 3 June 2008 (UTC))

Hi, TimothyRias. I've done a little copyediting to improve the English. I hope I haven't introduced any mistakes.

Thanks. I'll respond point by point if you don't mind. (TimothyRias (talk) 08:38, 4 June 2008 (UTC))

IIRC the article used to have, just after the paragraph about particle accelerators, 1 or 2 sentences which said that collisions at least as energetic occur naturally in the upper atmosphere all the time; since these apparently do not produce micro black holes, this is another reason for believing that particle accelerators wil not produce micro black holes. Was that correct? If so, I suggest it should be restored, as non-specialists will find it easy to understand and therefore reassuring.

Well, it is not quite correct. Cosmic ray argument merely insures that nothing catastrophic will happen. This does not imply that no micro black holes are created. They could either be highly unstable (as expected) in which case they could go by unnoticed. They could even be stable and just have hardly any effect on other particles. A 1 TeV blackhole travelling through solid lead at the speed of light would take a very very long time (longer than the age of the universe) to double in mass, so micro black holes would basically act as WIMPs. I'd did tweak the text a bit to stress that black holes are more likely to be created in cosmic ray events than in the LHC. (TimothyRias (talk) 08:38, 4 June 2008 (UTC))

Under "Growth", what do you mean by "black hole will absorb a pretty constant amount of interstellar dust and cosmic background radiation"? Does it not depend on the local densities?

That might need some tweaking. I merely wanted to confer that there is a continual supply of these sources of matters. Of course, the amount of dust will vary with the local density. (Although unless we have a very rapidly moving black hole these densities should not vary to violently.) (TimothyRias (talk) 08:38, 4 June 2008 (UTC))

What's maximum diameter of a black hole lighter than the moon? The points that by every-day standards the moon is alarge object, so the diameter would help to put it in perspective.

Its about a tenth of a millimeter. It is mentioned in the current sizes section, but it might be wise to mention again. (TimothyRias (talk) 08:38, 4 June 2008 (UTC))

The final sentence says, "... could even —although current developments in quantum gravity— hypothetically ..." The part "—although current developments in quantum gravity—" looks incomplete. What did you intend to say? Philcha (talk) 15:23, 3 June 2008 (UTC)

Fixed. (I wanted to say that there are no indications that micro BHs would be stable in quantum gravity.)

(As a minor remark degrees Kelvin are denoted without a degree mark.) (TimothyRias (talk) 08:38, 4 June 2008 (UTC))

OK, I replaced the old content, with the new. It may still need a lot of improvement but it should at least be better than the old content. (TimothyRias (talk) 10:04, 9 June 2008 (UTC))

Evidence section

In previous version of the article, the information covered in the current techniques for finding BHs and BH candidates section was covered in a section called evidence. I think it might be wise to reinstate such a section (and thus merging the two section mentioned above) for several reasons:

1. Many readers will be skeptical about the concept of BHs. A section presenting the evidence leading to the current scientific consensus that BHs exist would be very welcome for them.
2. As far as I know, the evidence we have goes little further than the observation of compact objects with masses above the TOV limit. Extrapolation of the laws of physics as we know them (GR + QFT) then leads to the conclusion that these objects can little else than BHs. None of the features typical to BHs (like Hawking radiation) have been observed. This article should probably reflect this status.
3. I believe that such an approach would provide more structure to the current sections.

This section should probably also include a subsection on the possible alternative explanation for the BH candiates like Gravastars, Fuzzballs, quarkstars, etc. (This can probably absorb the current alternatives section. We can probably also trim down the candidates section since much of what is covered there is covered in much more detail in the stellar black hole and supermassive black hole articles. So providing only a brief overview here and linking to the other pages could be a nice solution.(TimothyRias (talk) 10:15, 13 May 2008 (UTC))

"No Hair" No Way?

The "No Hair" Theorem as presented here and in the "No Hair" Wikipedia article is either poorly presented or just plain wrong.

Maybe the problem is a lack of distinction between the singularity itself and the event horizon. At the very least, event horizons possess the property of location. Otherwise, all event horizons in this universe are located in the same spot!. Regarding the various event horizons and their surrounding phenomena, I believe my blog - hrwertmuller.blogspot.com - describes the subject quite well, even tho I am saying so myself.

"Singularities" on the other hand, may be in a "universe unto themselves". Me no grok the math. -Harry Wertmuller HarryWertM (talk) 21:16, 1 June 2008 (UTC)

You could add position, and momentum to the properties, but the more usual approach to the subject is to consider the black hole in its own rest frame. (fixing the position en velocity.) Other properties such as the location of the event horizon are not independent of the three properties mentioned here (mass,charge and angular momentum.), but are merely a function of these properties. Anything you want to know about the black hole (in its rest frame) can be computed from these quantities. (anything you would want to know in any other frame (i.e. about a moving black hole) can be obtained by suitable coordinate transformations.) (TimothyRias (talk) 14:16, 2 June 2008 (UTC))

Well, I would add position and momentum. It seems to me the "usual approach" you describe for Black Holes would be akin to a "usual approach" of always mapping our Solar System from the view of the center of the galaxy. A poor presentation for most people.

And what about magnetic fields? If the stuff between the singularity and the event horizon has spin and charge, is there no magnetic field outside? And if same is wobbling, what about appropriately long wavelength electromagnetic waves outside? HarryWertM (talk) 21:51, 2 June 2008 (UTC)

Stuff like the magnetic dipole moment, are completely determined by the the three properties mentioned above. The dipole moment of a black hole for example is just a function of its angular momentum and charge.

Properties like the velocities are not properly properties of the black hole itself. When viewed by itself these properties make very little sense. These properties only have meaning when the black hole is view with relation to some other object. In such a situation the relative velocities are properties of the system as a total. These should not be included with the list of internal properties, when studying the black hole by itself. (TimothyRias (talk) 11:18, 3 June 2008 (UTC))

"The dipole moment....is just a function..." OK. And electrons; protons; and neutrons and atomic isotopes are all just a function of quarks, so maybe an article on the hydrogen atom should not mention all those things. But I would.

"Should not be included....when studying the black hole by itself." Only a few unification theorists study black holes and their insides by themselfs, like what happens to the Standard Model inside a black hole. That's what "No hair" is mostly about - no normal QM. This whole "no hair" subject seems like a candidate for removal to some separate article...."QM Inside Black Holes"?? HarryWertM (talk) 16:25, 3 June 2008 (UTC)

I would say that pretty much all theorist studying black holes, study black holes by themselves. But you are still completely missing the point. The "no hair" statement is that a the state of a black hole is completely specified by a small number of parameters. This makes BHs extremely odd objects. Macroscopic objects like stars tend to have a huge amount of internal degrees of freedom. So, many that describing the state of such an object at any one time is practically impossible. BHs on the other hand have just three parameters that completely specify their state.

Also, your first remark "electons,... function of quarks" makes little sense (beside the fact the electrons are elementary particles and do not consist of quarks). A neutron is build up out of quarks, but that doesn't make it a function of quarks. That last part would only make sense if "quarks" was a quantity. Knowing what quarks build up a neutron will tell you nothing about the state of the neutron. On the other hand if I know the mass, charge and angular momentum of a BH, i can then calculated any other property of the black hole you would want to measure (such as the magnetic dipole moment). (TimothyRias (talk) 08:54, 4 June 2008 (UTC))

Right. I was completely missing the point. Black holes are extremely odd objects which can be totally described by very few parameters. A good sentence. Start another article and make that sentence the opening line.

Much of the most complex exposition in the main article, reflecting the most complex discussions on this talk page, might well be removed from the main article and placed in an article titled "Black Hole Physics". Proton decay. Formation. Evaporation. Possible sizes. Micro holes. Debate over accelerator hazards. Leave tha main article focused on history; experimental evidence for existence; exterior effects like gravitational lensing; et cetera.

And believe it or not, I still say no hair no way. Somewhere I saw the word superfluid. A BH is like a very dense superfluid. So it could not wobble like a precessing solid gyro. But surely infalling matter can carry angular momenta unaligned with pre-existing angular momentum. Then what do you get? Vortices? Would not a ball of liquid helium floating in space be a somewhat relevant model?

And with charge then you have something more than a simple magnetic dipole. An outrageously complex multipole mess.

And changes due to infalling matter create other questions. Like: What is the speed of gravitational waves inside the Hole? If infalling matter increases the size of the Hole, does it grow with lumps? Growing perfectly spherically implies an infinite speed of propagation for gravitational force throughout the Hole.

Maybe not hairy, but really, really messy. --Harry Wertmuller PS-Thanx for time & patience in responding to me. HarryWertM (talk) 23:32, 10 June 2008 (UTC)

What makes it impossible to escape from black holes? (2)

Hi, TimothyRias, I really like your approach to "What makes it impossible to escape from black holes?" However it omits one point, why even powered objects such as extremely powerful spaceships with plenty of fuel / reaction mass can't escape. IMO this is important, because the Newtonian model can't explain this, i.e. this question shows how the GR model is clearly superior from the point of view of a non-theoretician such as the typical reader. I think I can see how to incorporate it, but I'm sure you can do it much better than I can. Philcha (talk) 14:30, 2 June 2008 (UTC)

The point is in fact covered by the current treatment, although not explicitly. The current treatment says that at every point inside the black hole there is no direction you can go that will bring you closer to the horizon. This is akin to not being able to go faster than the speed of light in flat space (or back in time in Newtonian mechanics), no matter how much power you use the only directions you can go are towards the singularity. (TimothyRias (talk) 11:25, 3 June 2008 (UTC))

"The point is in fact covered by the current treatment, although not explicitly." I'm suggesting that: (a) for most readers it would be helpful to make it explicit, especially as it shows the superiorty of the GR model over the Newtonian explanation that still occasionally pops up in "popular" literature, and sometimes on this Talk page; (b) you can do this much better than I can. Philcha (talk) 11:30, 3 June 2008 (UTC)

I'll see what I can do. (TimothyRias (talk) 12:27, 3 June 2008 (UTC))

Thanks! Philcha (talk) 11:15, 4 June 2008 (UTC)

Micro black holes (mostly)

The article seems to me to be very gung-ho about "micro black holes". It seems to me it doesn't always fully take on board the implications of black hole thermodynamics.

Some specific concerns:

1. In theory there is no smallest size for a black hole. Once created, it has the properties of a black hole. (from section: Black hole#micro black holes).

• This is true only in purely classical GR. According to black hole thermodynamics, the entropy of a black hole with mass of the order of the Planck mass (about 2 × 10⁻⁸ kg or 1.1 × 10¹⁹ GeV/c²) is of the order of only 4π nats. An entropy this small means that there are only very few states the black hole can exist in, with only very few transitions possible between them. So any and all energy transfers between a black hole and its surroundings can be expected to become very granular, limited to only certain transitions.

Such a "black hole" essentially does not have the properties we associate with a black hole, because it effectively has no way to absorb any mass or energy infalling towards it, unless that energy is at least of the order of the Planck energy itself.

So it's not true that there is no smallest size for a black hole.

Here you are being very gung-ho about black hole thermodynamics. To date there is no decisive theory that the black hole entropy can be interpreted as the number of microstates of the black hole. (String theory and in particular AdS/CFT do give so an interpretation, but the proper interpretation remains unclear.) You're going over the top by saying that thermodynamics implies that there must be a smallest black hole. (But it is strong argument suggesting that a quantum gravity theory should give a lower bound.)

I also agree that there are many uncareful statements about (micro) black holes in the article. I've been working to improve the article, working from top to bottom. The quote comes from a part that still needs to be dealt with. Feel welcome to help improve the article. See, also the disccussion above. (TimothyRias (talk) 12:33, 4 June 2008 (UTC))

2. Section: Formation of smaller black holes - Evaporation of larger black holes.

• As the article correctly says a few lines later, a black hole with a mass larger than the moon will be gaining energy from the cosmic microwave background faster than it would be evaporating energy. So when the article says

If the initial mass of the hole was stellar mass, the time required for it to lose most of its mass via Hawking evaporation is much longer than the age of the universe

it's really rather missing the point. If the initial mass of the hole was stellar mass, the mass of the hole would actually be going in the other direction -- it would be increasing, not decreasing.

Agreed. I've been working on a draft version replacing this section here. This draft treats this somewhat better. Again feel free to help improve that draft so it can be included in the article.

3. Section: Formation of smaller black holes - Particle accelerators.

• IMO the article is far too glib about these suggestions. Comments like

Some speculative models allow the formation of black holes at much lower energies

fail to alert the reader to just how off the wall these suggestions are. The previous mention (in Black hole#Sizes), blithely suggesting that

According to some theories of quantum gravity they may also be produced in the highly energetic reaction produced by cosmic rays hitting the atmosphere or even in particle accelerators such as the Large Hadron Collider

is even worse.

Compare that to the rather more sanguine assessment in the micro black holes article:

Under standard theories, such an energy [1.1 × 10¹⁹ GeV/c²] to produce a micro black hole is orders of magnitude greater than that which can be produced on Earth in particle accelerators such as the Large Hadron Collider (LHC) (maximum about 1.15 × 10⁶ GeV), or detected in cosmic ray collisions in our atmosphere. It is estimated that to collide two aggregates of fermions to within a distance of a Planck length with the currently achievable magnetic field strength would require a ring accelerator about 1000 light years in diameter to keep the aggregates on track. Even if it were possible, any collision product would be immensely unstable, and almost immediately disintegrate.

This is a huge energy difference.

The new draft version of the formation section has more careful statements about this.

The huge difference you are mentioning is basically the result of the hierarchy "problem". (i.e. the planck mass being much smaller than the GUT-scale) It is not completely out there to suggest that a TOE would "solve" this in such a way that the actual Planck mass is much closer to the GUT scale (braneworld scenarios do precisely this). In such a situation the creation of black holes could come in range of cosmic ray collisions or even the LHC. Of course, as most quantum gravity theories this is mostly speculation. But the creation of micro black holes at lower energy scale is seriously considered as a possibility. (TimothyRias (talk) 12:35, 4 June 2008 (UTC))

4. Section: Micro black hole escaping from a particle accelerator

• And then this whole section on the idea. Which again doesn't really emphasise the full scale of that energy gap; nor ISTM how very out of the mainstream the alternative theories are. (WP:UNDUE, anyone?)

There's also, I think, one other slightly misplaced notion in the section. Viz. that it's not really Hawking radiation that's the issue with micro black holes -- as the mass of a black hole comes down to Planck mass scales, one might well expect some quantum suppression of Hawking radiation, as the radiative Hawking particles needed would be becoming almost identical to the micro black holes themselves.

Rather, the problem is the small entropies, limiting the possible states of the black hole, so the black hole wouldn't be able to act in a "black hole"-like way.

And that's at the Planck scale.

Any more lightweight micro black holes, it seems to me, would have to be simultaneously both much much larger than the Planck length, to be able to interact with lower energy particles at all; and much much smaller than the Planck length, to still look like GR black holes at all, given their much smaller mass. I don't really see how tomfoolery with extra dimensions is supposed to be able to help here at all -- still less to fix up a shortfall in mass down from 10¹⁹ GeV/c² down to 10⁶ GeV/c².

Personally, I think this whole "Earth and BH" section should be scraped. Hopefully, when the other sections have been improved this section will have nothing more useful to add and can thus be deleted. (TimothyRias (talk) 12:36, 4 June 2008 (UTC))

5. It is presently unknown whether the much more energetic Large Hadron Collider [LHC] would be capable of producing the speculative large extra dimension micro black hole, as many theorists have suggested. (back in the "formation of smaller black holes section")

• "..as many theorists have suggested" seems to me, again, hopelessly misrepresentative of the balance of specialist opinion.

Agreed. No such statement should return in the new draft of that section. (TimothyRias (talk) 12:37, 4 June 2008 (UTC))

Also, a couple of other issues:

6. According to the "No Hair" theorem a black hole has only three independent physical properties: mass, charge and angular momentum. Any two black holes that share the same values for these properties are completely indistinguishable. This contrasts with other astrophysical objects such as stars, which have very many —possibly infinitely many— parameters. Consequently, a great deal of information is lost when a star collapses to form a black hole. Since in most physical theories information is (in some sense) preserved, this loss of information in black holes is puzzling. Physicists refer to this as the black hole information paradox.

• We actually set out in some detail, under Black hole#Black hole unitarity, why scientists generally agree that there is no puzzling loss of information. Viz.: in classical GR, as much information as you like can be stored in the space just above the event horizon of a black hole (as seen from the outside); while in a black hole with black hole thermodynamics, the information content of any infalling energy is accommodated in the change in the entropy of the horizon plus the entropy of the Hawking radiation.

So it is simply not true that a great deal of information is lost when a star collapses to form a black hole.

It is simply not true that scientists generally agree on there being no puzzle. Only last week there was a workshop in Paris discussing the issue, where most of the prime figures in the field heavily debated this. The problem is most prominent when you consider the evaporation of BH. Hawkings calculations show that no information comes out with the Hawking radiation; When and how this information should come out in QG is still up for debate. (TimothyRias (talk) 12:37, 4 June 2008 (UTC))

I think we need to be careful when we say that "no information comes out with the Hawking radiation". Hawking radiation has an entropy, so therefore there is an information content. Just because semiclassical techniques can only tell one about the ensemble average properties is in no way inconsistent with the assumption of a unitary deterministic evolution underneath.

Yes we may be nowhere near to an end-to-end micro-level description; but that's very different to saying that there is any indication that information is "lost" (in the sense of being non-unitarily destroyed, rather than just scrambled). Jheald (talk) 13:17, 4 June 2008 (UTC)

It is very simple. All calculations that we can do (except AdS/CFT), indicate that information is lost. This is a problem, because we believe that evolution should be unitary. Most phycists feel that a proper quantum mechnical understanding of the microstates of a black hole should fix this problem and a lot of them suspect that information should come out with the hawking radiation. But to date nobody has been able to show that it does. Specialists in the field such as Andrew Strominger will concede when pressed that both long lived remnants (implies no info in hawking radiation) and plain unpopular non-unitary evolution (maybe involving baby-universes) still belong to the logical possibilities.

You seem very keen on assigning BHs the Bekenstein-Hawking entropy and interpreting this as a measure for the microstates, but it just is not clear wether that interpretation is correct. (TimothyRias (talk) 13:51, 4 June 2008 (UTC))

I think it is an overstatement to say that "All calculations that we can do (except AdS/CFT), indicate that information is lost". Rather the calculations do not contain any detailed micro-level model, so have no way of modelling the subtle correlations in which one would believe the information to be preserved (if one does believe the information to be preserved). The calculations aren't able to indicate how information might be preserved. But that is very different to saying that they indicate that it is lost. Jheald (talk) 14:39, 4 June 2008 (UTC)

Calculations, like that of Hawking explicitly show that the final state has almost no information about the initial state. Most physicists think that this cant be right, and the there is an obvious culprit in the calculation namely the semi-classical way in which the backreaction was modeled. The moment you assume that there exists a detailed micro-level description of what happens you basically eliminate the problem by assumption.

Anyway this is not the place to have a lengthy discussion about this. (TimothyRias (talk) 07:56, 5 June 2008 (UTC))

7. It was later suggested that black holes are maximum-entropy objects, meaning that the maximum possible entropy of a region of space is the entropy of the largest black hole that can fit into it.

• It seems to me that this needs some care, and should perhaps be teased out further to stop people getting a wrong impression. While it's true that the maximum possible entropy of a region of space is the entropy of the largest black hole that can fit into it, so that a black hole is a maximum-entropy object for a particular volume of space, maybe it is worth noting that a black hole is not necessarily the maximum-entropy object for a particular quantity of mass or energy.

The entropy of the same amount of energy spread out as photons is considerably larger than that of a micro black hole, for example.

I think the article should at least note this, to prevent misconceptions. Jheald (talk) 11:40, 4 June 2008 (UTC)

In general, I agree, this article needs a lot of work. Pleas help out if you can. I personally feel that all the sections after the "BH candidates" section should either be integrated in the sections above, or moved to other articles. This goes especially for the "advanced topics" section. (TimothyRias (talk) 12:38, 4 June 2008 (UTC))

Sizes of Black Holes

Hi, TimothyRias, speaking as a non-expert I think the articles' beginning to look good - it strikes a nice balance between scientific detail and intelligibility to non-specialists. One thing that puzzled me about this time last year is the vagueness of the size ranges, e.g. for the Tolmann-Oppenheimer-Volkov limit. I remember reading last year that it depends on the chemistry of the individual star. I interpreted that as meaning that: if the star's composition and that of infalling matter are dominated by easily-fusible (mainly lighter) elements, a greater mass is required for collapse, because the star is producing more heat to resist collapse; conversely if the star or the influx are dominated by heavier elements that require more energy to start fusion, a lower mass is required for collapse because the star is producing less heat. So:

• Is what I just said correct?
• If so, is there a simple, correct but fairly brief way to express this in the article? Philcha (talk) 13:13, 4 June 2008 (UTC)

What it boils down to is that we do not quite understand QCD well enough to describe the equation of state of a fluid of mainly neutrons. The values given for the TOV-limit thus suffer from significant theoretical uncertainty. (Note that the TOV-limit is the maximum mass of a neutron star before it collapses.) As for the size of the star needed to produce a neutron star heavier than that in in a supernova. Well, that can depend on a lot of factors, which mainly have to do with how much mass is shedded in the supernova. Factors in this include the density distribution of matter in the star and chemical composition (which are not unrelated).) In the end this is just a very complicated story. (TimothyRias (talk) 13:36, 4 June 2008 (UTC))

Thanks! There 2 points I think you should clear up about the TOV limit in the article:

• Why the TOV limit is vague. It may be difficult to do this in a way that's easily understood by non-specialists. Would something like this do: "While the principles that determine the Tolmann-Oppenheimer-Volkov limit are agreed, there is still some uncertainty about the exact mathematical details."
• Your last comment said "the TOV-limit is the maximum mass of a neutron star before it collapses." To me that appears to contradict "If the mass of the remnant exceeds ~3-4 solar masses (the Tolman-Oppenheimer-Volkoff limit) ..." Or perhaps I've misunderstood. Either way I think that part of the article needs clarification. Philcha (talk) 22:54, 9 June 2008 (UTC)

Responding to the last comment first. Any remnant heavier than the Chandrasehkar limit will condense to a neutron star. If the remnant is lighter than the TOV limit it will settle down in this state, if it is heavier (or becomes heavier due to further accretion of matter) it will continue its collapse further. And if nothing steps in to stop it it will form a black hole. So there is no contradiction here.

To the second comment, I don't think this should be clarified in topic about black holes. If people wonder about this they should follow the wikilink to the TOV article, which then should explain this further. (TimothyRias (talk) 09:54, 10 June 2008 (UTC))

Discussion of Large Hadron Collider risks

This subject has been knocking around several talk pages, here, LHC itself, and Hawking radiation, in particular. I have just proposed to separate the subject into a separate article; see the Talk:Large Hadron Collider page if you are interested. I think it could help to keep some of these other articles on-topic. Cheers, Wwheaton (talk) 19:40, 4 June 2008 (UTC)

This might be a good idea. I do for see many POV en original research issues for such a topic though. (TimothyRias (talk) 07:49, 5 June 2008 (UTC))

Yes, I expect that article to be a battleground, but at least I hope to confine the battle to one place, and not have it pop up on ten related article talk pages again and again. Then we can focus our attention to getting it right in one place, treating the issues fairly and as correctly as present knowledge permits. Devoutly to be wished... Wwheaton (talk) 21:26, 10 June 2008 (UTC)

"black hole resource letter"

An article forthcoming in the American Journal of Physics recommends this (current, 13 June or so, version of the) article, saying "As usual, this Wikipedia entry is surprisingly broad. The reference list is excellent." Well done all. Sdedeo (tips) 19:05, 16 June 2008 (UTC)

Etumology move to lead

Serendipodous, you just moved quite a large amount of text to the lead. I'm not sure this is a good idea. Etymology of physical terminology usually has at most anecdotal value and the true origin usually remains a mystery (as in this case) because the terms usually surface during discussions between people at conferences and for some reason stick. Anyway, the lead should be a reflection of the content of the article. You must agree that having 25% of the lead consisting of a discussion on the etymology not appearing elsewhere in the article does not do a good job at this. If we want to mention it in the lead at all, it probably should be a subsentence somewhere in the first paragraph when the term is mentioned. With the discussion where it belongs in the history section. (TimothyRias (talk) 08:45, 17 June 2008 (UTC))

Simplified Article

Might it not be a good idea to create a simplified version of the page for people who find this slightly confusing?

87.194.98.50 (talk) 17:23, 24 June 2008 (UTC)

Check out simple:Black_hole. Other than that, I think the intro of this article does a decent job of starting at an accessible level, and getting more detailed as you go on. -- Coneslayer (talk) 17:52, 24 June 2008 (UTC)

If after learning about Black holes, you are not at least slightly confused, then you haven't properly understood what has just been said. That being said this article should be as readable as possible. Especially the first sections. The article will at some point have to touch on some of the more complicated issues. (TimothyRias (talk) 10:17, 25 June 2008 (UTC))

Please fix the Cockneyism

"While the mass of a black hole can take any (positive) value, the other two properties —charge and angular momentum— are constrained by the mass. In natural units , the total charge Q and the total angular momentum J are expected to satisfy Q2+(J/M)2 ≤ M2 for a black hole of mass M. Black holes saturating this inequality are called extremal. Solutions of Einstein's equation violating the inequality do exist, but do not have an horizon. These solutions have naked singularities and are thus deemed unphysical. The cosmic censorship hypothesis states that it is impossible for such singularities to form in due to gravitational collapse. This is supported by numerical simulations.[citation needed]"

Mos' peo'le (except those who speak Cockney) do no' pronounce horizon as 'orizon, so i' should say a horizon. Ta! 98.31.54.35 (talk) 08:03, 27 June 2008 (UTC)

Please feel free to fix a typo when you see it - thanks! PhySusie (talk) 17:41, 27 June 2008 (UTC)

He/She couldn't because the article is semi-protected. (TimothyRias (talk) 19:41, 27 June 2008 (UTC))

"an horizon" is proper British English -- "an" is used before [h] when the word is not accented on the first syllable ("an historical event" but "a history"). —Preceding unsigned comment added by 76.199.66.94 (talk) 13:03, 29 June 2008 (UTC)