Talk:Black hole/Archive 6

message: I recently read an article in Scientific America stating that "as matter whips around a black hole, it radiates light perpendicular to its orbital radius."  This doesn't seem plausible, as it has been stated that black holes pull in light (in the wikipedia article as well). - Akios.Metta 08:00, 11 November 2006 (UTC)
replies: text: You are probably talking about photons coming out of the accretion disc. As long as the photons didn't pass the event horizon they can escape the pull of the black hole.Melamed katz 20:48, 11 November 2006 (UTC)
thread_title:  Black Hole Emitting Light? 

message: How is it that "observable" emissions from black holes (ultraviolet rays, etc) are even observable in the first place? All frequencies of radiation on the electromagnetic spectrum travel at the same speed: the speed of light. If light (I'm assuming visible light) cannot escape, how can X-rays? Ninetigerr 06:36, 16 November 2006 (UTC)
replies: text: Black hole#Observation covers this already. The radiation is emitted by material orbiting outside the event horizon where light can still escape (or in the case of Hawking radiation it's emitted from the empty space just outside the event horizon). Bryan 06:48, 16 November 2006 (UTC)
thread_title:  Irony in the article 

message: This sounds stupid, but would it be possible to colonize a black hole? Please respond to this question. Mrld 02:33, 27 November 2006 (UTC)
replies: text: The short answer is "no", the long answer is "Nnnoooooo!" But see Frederik Pohl's Heechee series for an interesting sci-fi treatment of the subject. Doc  Tropics 02:48, 27 November 2006 (UTC)

text: It's not stupid.  Certainly, we couldn't colonize a black hole in the sense of "landing on it".  However, it would be possible (theoretically) to put a space station in orbit around a black hole, or even build some large structure (a ring or a sphere, for example) around (but outside of) the black hole.  The reason for doing this is that spinning black holes could actually serve as energy sources.  There is something called an ergosphere around a spinning black hole, outside of its event horizon.  It is theoretically possible to throw something into the ergosphere and get back something with higher energy.  The practical details of how to do all this are -- of course -- well beyond our current abilities.  --MOBle 19:33, 2 December 2006 (UTC)
thread_title: Colonize Black Holes

message: I'm not a big fan of this addition. I think the existing article is very clear, and certainly understandable by anyone with a middle-school education. The new section is redundant, and it itself needs work on tone and clarity. Thoughts? —The preceding unsigned comment was added by 169.229.95.134 (talk) 03:05, 10 December 2006 (UTC)
replies: text: The concept is not necessarily clear to such people; this addition was prompted by queries which made that clear. Reading the article, it explains in scientific terms that a bblack hole is "an object with a gravitational field so strong that nothing can escape it", and covers the history and formation and evidence for/of them. But it doesn't describe, in laymans intuitive terms, what a black hole actually is. That's a common problem with some types of articles. It's easy to assume knowledge and background that many readers don't have. A summary overview that explains a scientific concept in lay-terms is often very beneficial as a sort of orienting overview of counter-intuitive concepts such as a mass collapsing into a zero (as opposed to small) space (singularity), and placing that in the context of "normal" matter. A student or lay-person with little physics knowledge can read the two paragraph overview and gain a fairly accurate understanding of the field, including enough understanding to make sense of (or discuss) other aspects of the topic. Some touching up might not hurt but the basic idea is valuable. FT2 (Talk | email) 03:37, 10 December 2006 (UTC)
thread_title:  "Simple Overview" 

message: This useful looking table was on the french wikipedia. Any use?
:
 Types théoriques de trous noirs en fonction du moment cinétique (J) et de la charge électrique (Q). La masse (M) est toujours strictement positive.
 	M > 0             	M > 0
 	J = 0             	J ≠ 0
Q = 0 	Schwarzschild     	Kerr
Q ≠ 0 	Reissner-Nordström	Kerr-Newman
FT2 (Talk | email) 02:13, 11 December 2006 (UTC)
thread_title:  Table? 

message: Hello, I've added a table with the nearest candidates. Please double-check. Have fun. Dream about visit. -- Rwst 17:10, 15 December 2006 (UTC)
thread_title:  nearest candidates 

message: There should be an article for Black holes in fiction, similar things exist for a lot of stars and there is even one for White holes in fiction.  Or does it exist somewhere under another name?  There is a bit in Black hole (disambiguation), but very little.
Creatures of Light and Darkness contains the concept, though not the name, something called Skagganauk Abyss where there is no space or time.  I'm fairly sure I also recall an SF story that features something we would now call a Black Hole, probably taken from the author's reading of science.
--GwydionM 20:10, 21 December 2006 (UTC)
replies: text: Now added.  --GwydionM 17:56, 23 December 2006 (UTC)
thread_title:  Black holes in fiction? 

message: This failed GAC for these reasons: the biggest problem is that it's undercited. One section has no cites. Multiple paragraphs, several in a row have no cites. Refs come after punctuation, not in the middle of a sentence. The X-1 photo has a tag that it's about to be deleted.Rlevse 03:28, 7 January 2007 (UTC)
thread_title: GA failed

message: The alternative models section mentions plasma cosmology in a rather etherial style.  Since plasma cosmology is not accepted as mainstream science, perhaps this bit should be removed. Man with two legs 17:34, 11 January 2007 (UTC)
replies: text: It's worth summarizing some of the alternative and opposing views; if nothing else it is relevant to balance and also provides relevant ideas of other people's proposals related to black hole observations and theory. But it shouldn't be promoted as such, just stated as factual, and the space or approach should also reflect its support base - scientists or not, tiny or notable, and so on. But just because it's not mainstream scientifically accepted is not, by itself, the criterion for appropriate removal. FT2 (Talk | email) 20:53, 11 January 2007 (UTC)
thread_title: Alternative models: plasma cosmology

message: I came here to check for information on charged black holes, their magnetic fields and the interaction with an accretion disk. But there doesn't appear to be much coverage of this topic, whether here or on the charged black hole page. I'd think this an important, if not vital sub-topic as it relates to relativistic jet formation, for example, which regulates galaxy mass accumulation, &c. So I'd like to include this on the to-do list for completeness. Thanks. — RJH (talk) 23:32, 11 January 2007 (UTC)
replies: text: Any black hole of stellar dimensions or larger would not have a significant charge. If there were one, charged ions of the opposite charge would quickly be drawn into it and neutralize its charge. JRSpriggs 08:03, 12 January 2007 (UTC)
replies: text: True, a black hole is likely to have a very small charge, however, it certainly can have a tiny bit of charge.  I can try to take some time on ADS to see if I can dig up a paper on the subject - you're right,the charge and B-field of a black hole is likely to be insignificant.  But perhaps not uninteresting - I've certainly discussed the subject in a professional setting as an astronomer, if only of idle interest. WilyD 14:42, 12 January 2007 (UTC)
replies: text: Thanks. If not from charge then perhaps something on the generation of a relativistic jet from the rotational energy of the black hole, in combination with the magnetism of the accretion disk? I.e. how is the energy transferred from the black hole to the jet? The concept is unclear enough in my mind that an explanation on this page would be helpful. — RJH (talk) 22:35, 12 January 2007 (UTC)
replies: text: I think that the energy driving the jets is coming from the accretion disc rather than the black hole itself. I am just guessing, but I think that the gravitational energy of infalling material is converted to kinetic energy in the disc and then a small part of it goes to heat due to friction and then it shoots out sideways in the jets because it cannot go back out via the equator which is full of accreting stuff. The plasma in the disc captures and amplifies ambient magnetic fields as it spins and they force the escaping particles into a narrow beam. JRSpriggs 04:51, 13 January 2007 (UTC)
thread_title:  Charged black holes & magnetic fields 

message: There is an error in the simple overview section. Gravity is an extreamly weak force and is not responsible for keeping subatomic or atomic particles together. This section should briefly mention the strong and weak nuclear forces. —The preceding unsigned comment was added by 63.78.207.104 (talk) 18:10, 20 January 2007 (UTC)
replies: text: I rewrote the section to correct that error. The force responsible for keeping matter from collapsing is the Pauli force which is a consequence of the Pauli exclusion principle, the Exchange interaction, and the Kinetic energy resulting from the Uncertainty principle. Gravity, Electromagnetism, and the Strong force all tend to pull matter together. Gravity is dominant only for very large bodies. I do not think that the Weak force is a significant player in this, so I did not mention it. JRSpriggs 11:47, 21 January 2007 (UTC)
thread_title:  error in the simple overview section 

message: I heard that if the sun were to be a black hole of the same mass, nothing would happen to the planets, they won't "fall" in the black hole. However, the gravity of the black hole is so powerful that things within the black hole's horizon have no hope of coming back. So, if the sun were to be a black hole, where its horizon would be located and why planets would not "fall" in the black hole despite its overwhelming gravitational force? —The preceding unsigned comment was added by 24.201.98.14 (talk) 17:27, 22 January 2007 (UTC)
replies: text: One thing, thinking about general astro physics, not only black holes by themselves, is that so much energy is released if the sun collapsed to a black hole, it would be a supernova. The outer parts would be ejected in high speed, have large effect on the planets. -- BIL 08:43, 29 March 2007 (UTC)

text: Inside the spherical shell the gravity is NOT zero.  Between the original radius and the event horizon gravity increases exponentially as one moves towards the center, producing enormous tidal forces and the famous spaghettification effect.--kwg06516 22:46, 19 April 2007 (UTC)
replies: text: You seem to be misreading the example given. The relevant part was "under Newtonian gravity, both a spherically symmetric star and a same-mass black hole are equivalent to point masses", meaning their effects on objects distant from them are identical. The shell discussion was part of the proof for this equivalence. --Christopher Thomas 23:05, 19 April 2007 (UTC)
thread_title:  If the sun were a black hole 

message: Can someone explain what that is?  Maybe an article about it would help--there isn't one now. 67.117.130.181 22:23, 15 February 2007 (UTC)
replies: text: I think you are looking for Kruskal-Szekeres coordinates. It does need more work and a diagram or two. JRSpriggs 07:47, 16 February 2007 (UTC)
replies: text: By the way, where in this article is "Kruskal diagram" mentioned (the subsection and paragraph number)? JRSpriggs 08:07, 18 February 2007 (UTC)
replies: text: The Kruskal diagram is a spacetime diagram that lets you figure out the order of events near the boundary of a black hole.  It's not mentioned in the article but there are a fair number of Google hits for it.  I heard about it in astronomy class and had hoped to find out more about it here.  It's somewhat hard to understand from the references I've looked at, given my very limited prior knowledge.  Thanks. 67.117.130.181 09:09, 19 February 2007 (UTC)
replies: text: See section 31.5 of Gravitation (book). JRSpriggs 09:49, 19 February 2007 (UTC)
replies: text: The Kruskal-Szekeres diagram is basically the antecedent to the Penrose diagram (which has just been added to this article in the "Possibility of escaping from a rotating black hole" section). The difference is that the KS only shows the immediate area around the black hole, while the Penrose uses conformal "crunching" to represent the entire universe[s] outside of the hole. Also, for some reason, KS diagrams generally show the singularity as a slightly parabolic (curved inward), where in Penrose diagrams, they are straight, horizontal lines.Eric B 16:58, 8 May 2007 (UTC)
thread_title:  Kruskal diagram 

message: Theoretical physics is a really tough subject for an encyclopedia, since readers can range from 12-year-olds (or younger) to physics undergraduates (not to mention science fiction enthusiasts or would-be writers looking for background). I don't see how a single presentation of a subject like black holes can meet the needs of audiences at both ends of the range.
So I suggest the article should be restructured into 2 major sections, or possibly separate but linked articles, one "popular" and one "technical".
The popular section / article would contain:
* Non-technical definition. It would still have to mention general relativity in order to explain why a spaceship can't escape, because a Newtonian explanation only explains why unpowered objects and particles can't escape.
* Anatomy of a black hole: singularity, event horizon, ergosphere (if the hole spins fast), etc.
* Formation of black holes.
* Evaporation of black holes via Hawking radiation.
* Black holes at the centers of galaxies.
* Black holes and earth (as at present).
* Link to wormhole with brief note.
* Black holes in fiction. BTW at the time of writing I can't find in this article a link to a separate article "Black holes in fiction", as discussed above.
* Link to "Alternative theories" section of the "technical" page / section, plus very brief description (more of a note).
"Technical" page / section: all the other content.
I would prefer separate pages, since that both articles would still be pretty long. I think the "popular" page should be the main entry, since more readers of Wikipedia are likely to be non-technical, but the "popular" page should have a link to the "technical" page at the top and in "see also".
The "popular" page would have to be checked by a competent physicist (I'm not even an incompetent physicist) to ensure that it contains no more distortions than those that are inevitable when describing a highly mathematical subject in plain English. Then it might be a good idea to lock it, to prevent editing without competent supervision. I think the "technical" page should remain open, sop that new theories and discoveris can be incorporated.
Question: May, Moore & Lintott's book "Bang!" says (p 77 in UK edition) that the orbit of a star labeled S21 proves there's a large black hole at the centre of the Milky Way - the orbit's minimum radius is 17 light-hours so that limits the radius of the central body, the orbital period is 15.2 years and that determines the mass of the central body, and the central body's mass and maximum radius mean it has to be a black hole (discounting the exotic alternatives to black holes). Can anyone find an academic reference which describe this analysis? I've googled and found nothing.
Note: http://cosmology.berkeley.edu/Education/BHfaq.html has a good FAQ, which should be in the "links" section of the "popular" page.Philcha 14:04, 17 February 2007 (UTC)
replies: text: Generally, we like to have articles begin with a non-technical explanation and work up to more technical stuff. Feel free to re-arrange the sections accordingly. As far as protection is concerned, that is determined by whether the article is a target for attacks by vandals, not by its level of sophistication. JRSpriggs 08:12, 18 February 2007 (UTC)
thread_title:  Possible restructure?

message: Does time stop at the event horizon relative to an outside observer, or is it just a false image portrayed by the delayed photons? If time stopped outside the event horizon, then wouldn't a black hole be frozen in time and what way would time be dilated within the event horizon? —The preceding unsigned comment was added by Emorej717 (talk • contribs) 20:08, 23 February 2007 (UTC)
replies: text: Time dilation does not work that way - but yes, it goes to infinity at the event horizon for an outside observer.  So does the redshift, however, so the object emits no radiation, as it stops moving. WilyD 20:29, 23 February 2007 (UTC)
replies: text: The event horizon is a light-like hyper-surface so events at the same place (but different coordinate-times) on that hyper-surface, although distinct, have no (spatial or temporal) separation. However, objects falling across the horizon continue to experience time while crossing and afterwards, until they are annihilated at the central singularity. JRSpriggs 08:56, 24 February 2007 (UTC)
thread_title:  Time Dilation 

message: Removed from the article:
:Finally, plasma cosmologists suggest that Birkeland currents provide an alternative explanation for the observed phenomenon, whereby plasmas transfer energy over great distances to smaller regions where it may be periodically or catastrophically released. Anthony Peratt explains the flickering of electromagnetic radiation: "The flickering of a light in Los Angeles does not mean that the supply source, a waterfall or hydroelectric dam in the Pacific Northwest, has abruptly changed dimensions or any other physical property. The flickering comes from electrical changes at the observed load or radiative source, such as the formation of instabilities or virtual anodes or cathodes in charged particle beams that are orders of magnitude smaller than the supply. Bizarre and interesting non-physical interpretations are obtained if the flickering light is interpreted by a distant observer to be both the source and supply." Plasma cosmology in this manner is a minority view not within mainstream science
This basically functions as an Unduly weighted advertisement for plasma cosmology. According to science notability and fringe reporting standards, this coverage is not warranted here since plasma cosmology is ignored in both the mainstream and in the popular press. No one takes Peratt, for example, to be an expert in black hole alternative models. --ScienceApologist 19:45, 1 March 2007 (UTC)
thread_title: Alternative explanation paragraph excluded

message: this article is great but, it needs a lot of work.ψ —Preceding unsigned comment added by Drock211 (talk • contribs)  00:31, 6 March 2007 (UTC)
replies: text: WP:SOFIXIT Could you be more specific? JRSpriggs 06:51, 6 March 2007 (UTC)
replies: text: It could use more in-line citations, especially when it comes to the parts about describing what the actual black hole really is. Diez2 16:43, 7 March 2007 (UTC)
replies: text: The biggest problem is that one can't say much about what a black hole is - our understanding of space-time breaks down inside of the event horizon (which is why the radii of black holes are given in terms of the event horizon and not in terms of what is inside). In fact, due to the cosmic censorship principle, it will be impossible (as far as we know now) to know what's going on inside the black hole. The only practical thing to do is talk about the black hole's effect on surrounding space. Saj210 01:39, 23 March 2007 (UTC)
thread_title:  work 

message: The article Rotating black hole says that space-time is dragged at the speed of light at the outer boundary of the ergosphere and faster than light within the ergosphere. It also says, "Particles falling within the ergosphere are forced to rotate faster and thereby gain energy. Because they are still outside the event horizon, they may escape the black hole," which implies that the ergosphere is entirely outside the event horizon. So:
* Is there any frame-dragging within the event horizon of a rotating black hole?
* How does the frame-dragging rate vary with increasing "depth" (a) between the outer boundary of the ergosphere and the event  horizon? (b) inside the event horizon?
* What happens just outside the outer boundary of the ergosphere? If space-time is dragged at less than the speed of light, is it possible for an object just outside the ergosphere to drain rotational energy from the black hole? If there is no dragging, why is there a discontinuity?Philcha 21:56, 17 March 2007 (UTC)
thread_title: Rotating black holes: frame-dragging at / within event horizon?

message: The article Rotating black hole says a rotating black hole has 2 event horizons, inner and outer. What are the consequences of this? For example does it mean that a completely external observer can see nothing within either horizon, an observer within the outer horizon can see things within the outer horizon and outside it but not within the inner one (as well as outside the outer horizon), and an observer within the inner horizon can see things which are within the inner horizon and outside it?
:I've just added an image of Penrose diagrams of three types of black holes, including the rotating and/or charged ones, with the 2 horizons, and this should answer your question. As you will notice, each successive horizon lies in the "future" of an observer approaching it, so once you are inside of one, you can look back at it (though there's nothing to see at that point since it is an imaginary "boundary"), but you cannot see one you are outside of, since it in effect "approaches" you at the speed of light. Once you pass through the midway point of the timelike wormhole, then you pass through another pair of horizons into one of another pair of universes.Eric B 17:10, 8 May 2007 (UTC)
replies: text: Thanks, Eric B. But I think the article is more likely to be read by non-specialists, and the Penrose diagrams will not help them much. Can you summarise it in plain English?Philcha 09:37, 10 July 2007 (UTC)

text: It's a limiting case. And a very sketchy one at that. That's getting into the whole notion of "naked singularities", which is purely hypothetical, and noone knows if it is possible. I myself have never seen a specific limiting speed given, and they may not know, or it is probably proportional to the mass and radius. (Different speeds depending on those factors).Eric B 17:10, 8 May 2007 (UTC)
thread_title: Rotating black hole: 2 event horizons

message: Rotating black hole says, "Due to the two event horizons, a rotating black hole is also required to have two photon spheres, an inner and an outer one. The greater the spin of the black hole is, the farther from each other the photon spheres move. A beam of light travelling in a direction opposite to the spin of the black hole will circularly orbit the hole at the outer photon sphere. A beam of light travelling in the same direction as the black hole's spin will circularly orbit at the inner photon sphere." This raises a lot of questions for non-physicists like me:
* Are a a rotating black hole's photon spheres true spheres, or are they oblate like the ergosphere?
* What are the limiting conditions for possible photon orbits in the 2 photon spheres (for non-rotating BHs, the semi-major axis can't be smaller than the Schwarzchild radius)?
* What happens to the outer sphere at extremely high spin speeds, when the radius of the outer event horizon is close to zero? And what happens to the outer sphere at the limiting spin speed, when the radius of the outer event horizon is actually zero? How far can it extend?
* If a photon grazes the edge of a photon sphere but at an angle to the spin plane, what happens to the component of the photon's motion normal to the spin plane?
* Does the outer photon sphere have any effect on a photon travelling tangentially to the inner photon sphere and in the same direction as the black hole's spin?Philcha 23:27, 17 March 2007 (UTC)
thread_title: Rotating black hole: 2 photon spheres

message: As far as I understand it (?????), the "no hair" theorem implies that black holes have no temperature but the Hawking radiation theory implies that they do. Is there a conflict?Philcha 10:34, 21 March 2007 (UTC)
replies: text: The "no hair" theorem (NHT) states that a black hole has no other caracteristics beyond its mass, eletric charge and angular momentum. In other words, two black holes that have exactly the same value for these three quantities are completely identical in all respacts, since there are no other caracteristics by which they could be distinguished from each other. The NHT does not prevent these black holes from having a Hawking temperature because their temperature is not an independent quantity. (given the other threee, the temperature can be calculated). Dauto 20:03, 22 March 2007 (UTC)
replies: text: Thanks! I've edited the "no hair" section to emphasise "independent".Philcha 10:01, 23 March 2007 (UTC)
thread_title: Conflict between "no hair" theorem and Hawking radiation?

message: Should the article have a "Theoretical dilemmas" section which summarises, in the simplest possible language, some of the difficulties in current black hole theory? It could also refer to e.g. the quantum mechanics objections to the zero-volume singularities predicted by general relativity. If such a section is added, I suggest it should be placed at the end of the plain-language theoretical material and just before the sections about finding black holes.Philcha 10:34, 21 March 2007 (UTC)
thread_title: Need for a "Theoretical dilemmas" section?

message: I've seen various plain-language explanations of why nothing can escape from within the (outer) event horizon, e.g. Black_hole#What_makes_it_impossible_to_escape_from_black_holes? currently says both "bend space-time so much that, at all points within a certain distance of the center (within the event horizon, see below) all directions lead to the center" and "bends space-time so tightly inside the event horizon that: space and time swap roles." From other reading, e.g.  I've concluded that "space and time swap roles" is the best I've seen, since it prepares the way for what the inner horizon does in rotating black holes - any event horizon makes space and time swap roles, the outer one makes the location of the singularity a falling object's future, the inner one reverts space & time to their normal roles (I'm still struggling to grasp the implications, but that's another matter). But how to explain this swapping in simple terms?
:I've made an attempt at explaning the "switch" at Changing places, but it's certainly not easy to get that particular point across without explaining spacetime diagrams, light-cones and all that stuff. Markus Poessel 14:46, 1 May 2007 (UTC)
thread_title: How to explain space & time swapping roles at event horizons?

message: Out of the curiousity I wanted to habe a look at the FA nomination and removal discussions, but wasn't able to locate them. Does anybody know the links? --Pjacobi 16:36, 26 March 2007 (UTC)
replies: text: The first box at the top of this page (beginning "Black hole is a former featured article") has a "show" link at the right edge, alongside "Article milestones". Clicking this will show links to these discussions.Philcha 08:34, 27 March 2007 (UTC)
replies: text: Heavens, JavaScript wizards at work! Didn't notice this. --Pjacobi 12:09, 27 March 2007 (UTC)
thread_title:  Where are the FA discussions? 

message: A recent edit of Black_hole#Two_photon_spheres  has added "This beam will then split itself in two. Both pieces will move into the Hole." I think some clarifications are needed: (a) does it apply to only to the inner photon sphere (as the current wording implies) or to both? (b) why does the beam split and what causes the split? (c) why should both parts move inwards rather than e.g. one inwards and one outwards?Philcha 10:23, 28 March 2007 (UTC)
thread_title: Light in the photon spheres of a rotating black hole

message: I have temporarily marked a couple of paragraphs as "unreferenced" under "Objects which are thought to be black holes" and "Black holes and Earth".  I will add references on 9 April 2007 when I return to work.  (Expect something by John Kormendy.)  Dr. Submillimeter 22:13, 6 April 2007 (UTC)
thread_title:  Temporary "unreferenced" sections 

message: I've taken a good look at this article, and several sections seem to have changed into very strange states. I've made an attempt to bring them back into shape, without making any other major changes. This should wind down in another hour or so.
However, there are at least two other descriptions that could be added to the "escape is impossible" section that I don't feel up to writing right now. If WP:Physics lurkers or other denizens want to add them, great. One description is to define coordinates such that space near the hole appears to be flowing into it. In this description, light emitted outwards for the horizon propagates at C but doesn't get anywhere (in the more usual description, these are rays from the part of the edge of the light cone that's parallel to the black hole's worldline). A second description, from the old "fishing for the singularity" thread, defines coordinates such that the distance to the event horizon is actually infinite. This is good for giving a qualitative illustration of forces on any object attempting to fish things out being infinite. If neither of these descriptions is widely used, then by all means leave them out; the section just looks a bit strange saying "many descriptions exist, depending on how you set up coordinates" and then talking about only one of them.
I've also placed  tags at a couple of places in the escape section. It should be trivial to give suitable textbook references for them; I just don't have appropriate books handy. --Christopher Thomas 23:15, 9 April 2007 (UTC)
replies: text: I agree with your last comment ("many descriptions exist..." then talking about only one ...). In fact I don't find the description of tilting light cones helpful: it would require a (non-technical) definition of "light cone"; and a light cone's radius normally expands with time, so it would then be necessary to explain why light cones in a BH are no longer cones. Philcha 13:38, 17 April 2007 (UTC)
replies: text: Locally, they're definitely still cones (as locally, space can be treated as Euclidean). They just have the future light-cone pointing inward. See :Image:Bh-light-cones-1.png for a (rather ugly) diagram illustrating what I'm talking about. --Christopher Thomas 17:55, 17 April 2007 (UTC)
replies: text: Nice diagram! But I have reservations about using light cones: they're a convention / shorthand of relativity theory, and you have to understand the basic ideas first; how to explain to general readers why the light cones tilt?Philcha 10:24, 10 July 2007 (UTC)
thread_title:  Rewrite of several sections 

message: I'm just wondering if anyone know this, what would happen if two black holes collided?--Andy mci 09:14, 12 April 2007 (UTC)
replies: text: The two black holes would merge together to form a bigger one.  (At one point, it was theorized that some gamma ray bursts were produced when two black holes merged, but I am not certain if the theory is accepted any more.)  Dr. Submillimeter 09:23, 12 April 2007 (UTC)
thread_title: Black Hole hits Black Hole

message: Wouldn't light that passes near the event horizing be extremely red-shifted? —The preceding unsigned comment was added by Dragonfall (talk • contribs).
:Light emitted from near a black hole is red-shifted, but light from distant sources that passes near a black hole isn't. More accurately, it's blue-shifted on the way down and red-shifted by an equal amount on the way back up, with no net shift (unless the hole is rotating, but that's another story). --Christopher Thomas 02:03, 19 April 2007 (UTC)
thread_title: "Artist's Impression" near the top

message: In March 2007 I included in the "no hair" section a para on the limitations of the "no hair" theorem - in particular that it doesn't work if the cosmological constant is non-zero, and a non-zero cosmological constant is one of the more widely supported explanations for the apparent acceleration in the universe's expansion (summarised from the no hair theorem article). I notice this para has been removed. Why? Should it be reinstated? Philcha 23:41, 19 April 2007 (UTC)
thread_title: Limitations of "no hair" theorem??

message: This section says, "Second, the orbit is dynamically unstable; small deviations from a perfectly circular path will grow into larger deviations very quickly, causing the photon to either escape or fall into the hole." But the photon sphere only affects photons whose path is tangential. So why should such photons not follow a perfectly circular path? Philcha 23:51, 19 April 2007 (UTC)
replies: text: This was a rewrite of previous text which had implied that photons coming from outside the photon sphere could be captured into circular orbits in the photon sphere. I felt that this replacement version was more correct. Regarding the current version, aligning a photon along a perfectly tangential orbit requires infinite precision and zero divergence, both of which are unphysical (even if it's initially set propagating on a tangential path with infinite precision, its wavefunction will spread out above and below the photon sphere, resulting in continuing attenuation of the component that stays on the sphere). --Christopher Thomas 00:04, 20 April 2007 (UTC)
thread_title: Photon sphere of non-rotating, uncharged black hole

message: I plan on summarizing the "Black hole candidates" section to some degree.  The reader really needs to be referred to other articles for more extensive discussions of these specific classes of objects.  Also, the section tends to be comprised of a series of statements from random press releases that are written with huge amounts of hype.  These statements do not present a coherent overview of the field of black hole observations, so I will be removing some of them in favor of review material on black holes.  Dr. Submillimeter 21:04, 21 April 2007 (UTC)
thread_title:  Summarizing the "Black hole candidates" section 

message: This article is a magnet for vandalism.  What do other people think about asking for protection for this article?  That could restrict anonymous users from editing the article.  Dr. Submillimeter 09:42, 24 April 2007 (UTC)
replies: text: 14 of the past 50 edits are some form of vandalism.  I think some type of protection is in order.  I'll go ask.  Dr. Submillimeter 14:52, 24 April 2007 (UTC)
thread_title:  Vandalism protection 

message: This is a topic that is very interesting to me I am trying to understand this very difficult topic in my paradigm.  I understand basic science principle the law of conservation of energy, it states that energy cannot be created or destroyed—it can only be changed from one form to another (such as electrical energy into heat energy).   I also understand we are talking about Quantum Physics.  So my question is how is a black hole possible?  I ask this question because of what the article says about empty space:
While general relativity describes a black hole as a region of empty space with a   pointlike singularity at the center and an event horizon at the outer edge, the description changes when the effects of quantum mechanics are taken into account. The final, correct description of black holes is unknown (it requires a theory of quantum gravity).
—The preceding unsigned comment was added by 168.169.157.184 (talk) 14:47, 27 April 2007 (UTC)
replies: text:  I came here searching if black holes are real or just theory. All the images are simulated, and I see theory as the popular word throughout the article. The impression the article leaves is it black holes are theoretical, but it should say so directly. Without a little summary blurb like this at the beginning, this article is like it contains nothing of value for none-science people. Can the lack of visual confirmed black hole be included in the introductory paragraph, or something like that? I hope to get someone else to do this. Because I can't. I wouldn't know where to research or cite. The introduction is all non-science guys ever read, help us understand at least that. Nastajus 06:22, 11 May 2007 (UTC)
replies: text: While black holes might appear to be only theoretical, a lot of observational evidence points to their existence.  See the citations in the Supermassive Black Holes section for examples.  The only reason why black holes have not been definitively declared to exist is because astronomers are still trying to demonstrate that these candidate objects really are only as large as their Schwartschild radii (although the possibility of these things being anything else is remote).  Dr. Submillimeter 08:37, 11 May 2007 (UTC)
replies: text: Empirical evidence strongly implies the existence of black holes.  While a black hole cannot be directly observed in the electromagnetic spectrum, a plethora of other factors indicate their existence.  For example, a frequent occurance is black hole/star binary system, in which a star orbits a black hole.  In order for the star to orbit this point in space, an object of sufficient mass must exist.  Other data, such as the emissions of X-rays and gamma rays from the accretion disks that often surround black holes, can be used to further confirm their existence.  To put it simply, absence of proof is not proof of absence. The Great Attractor 00:45, 25 May 2007 (UTC)
thread_title:  None science guy confused 

message: Since when is a black hole actually a black ball?  --Kirby♥time 18:06, 5 May 2007 (UTC)
replies: text: Depends on what you mean.  In a sense, black holes have always been black balls - seen from the outside, the boundary of the simplest kind of black hole is like the surface of a sphere.  And when you put a black hole in front of a luminous background, it looks like it does in the lead picture. Markus Poessel 19:43, 5 May 2007 (UTC)

text: Yes and no.  In front of a brighter background, it does act as a gravitational lens, of course (cf. the ring around the black disk in the lead picture - which isn't an artist's impression, but the result of a ((slightly simplified, as far as I remember)) simulation), but there's a remaining region from which no light reaches an observer. As for the airfoil example, there is one important difference: If you draw the (non-turbulent) flow of air around an airfoil, there will be regions where the flow lines are bent towards the airfoil and regions where they are bent in the opposite direction (the latter is necessary e.g. to get them all approximately parallel again behind the airfoil) Around a black hole, light rays are always bent towards the black hole. Markus Poessel 08:28, 8 May 2007 (UTC)
thread_title:  Lead picture... scientific consensus? 

message: "The 'No hair' theorem states that black holes have only 3 independent internal properties: mass, angular momentum and electric charge. It is impossible to tell the difference between a black hole formed from a highly compressed mass of normal matter and one formed from, say, a highly compressed mass of anti-matter, in other words, any information about infalling matter or energy is destroyed. This is the black hole information paradox." - black hole article
I believe this passage should be changed.  Unfortunately, Wikipedia has locked this article because "editors believe the current information is accurate." Steven Hawking created the concept that information was destroyed once it enters a black hole roughly thirty years ago, which created much debate because the black hole information paradox would destroy conventional physics by stating that "cause and effect" does not exist; information can be destroyed in the universe.  He came about this theory using his equation S=c^3kA/4hG.  However, recently he has come out and said this initial theory was wrong, that information is not destroyed in the universe.  He is currently arguing that information is moved from a universe with black holes to a parallel universe without black holes, using the black hole as a transport.  So far there is no evidence proving this theory.  I just believe we should be allowed to change this passage, considering even he has proven the black hole information paradox was incorrect. —The preceding unsigned comment was added by Elementalsurf7 (talk • contribs) 04:08, 6 May 2007 (UTC)
replies: text: Just for clarification, I requested semi-projection because of heavy vandalism attacks (with a little bit of spam) from anonymous IP addresses.  The article can still be edited by registered users.  Dr. Submillimeter 08:04, 6 May 2007 (UTC)

text: Would I be correct in my statement that the black hole information paradox is essentially that information (which supposedly cannot be destroyed) is absorbed by black holes, and through Hawking radiation, a black hole will dissipate and thus destroy the information?  I've never heard of that anti-matter-black-hole thing before... where did it come from? The Great Attractor 00:26, 25 May 2007 (UTC)
thread_title:  Black Hole Information Paradox Dispute 

message: This article seems to assume that all black holes are singularities.  Isn't there a type of black hole that consists of a neutron star with enough mass to have an event horizon but not enough mass to collapse into a singularity? 147.145.40.44 22:10, 9 May 2007 (UTC)
replies: text: No.  If it collapses inside its event horizon, it is impossible that it could avoid collapsing all the way (irrespective of its mass or the strength of the material it is made of). Man with two legs 16:59, 10 May 2007 (UTC)

text: What I wrote above comes from Einstein's general theory of relativity.  A complete theory of black holes would also have to make sense in terms of quantum mechanics and that is not yet complete.  So it is possible that someone will discover they don't exist after all, but most scientists believe they do exist. Man with two legs 15:05, 13 May 2007 (UTC)
thread_title:  Different types of black holes? 

message: Just a heads up, this article was mentioned in passing in a Nature news piece.   Antony-22 11:30, 19 May 2007 (UTC)
thread_title:  Mention in Nature 

message: I have to disagree with that statement at the beginning of the article.  As no electromagnetic radiation can escape, the black hole does not "appear" at all.  It is invisible.  The presence of black holes is only inferred from their gravitational interactions with surrounding objects, am I correct? The Great Attractor 00:57, 25 May 2007 (UTC)
replies: text: Well, black holes might emit Hawking Radiation, for instance, or gravitational radiation (although that stretches visible) WilyD 21:00, 24 May 2007 (UTC)
replies: text: Yes, but gravitational radiation, like black holes, has not been directly detected.  I may be nitpicking here, but to say a black hole "appears" black is inaccurate.  I think that line should be removed from the article.The Great Attractor 00:23, 1 June 2007 (UTC)
replies: text: First, sign your comments. Second, a black hole appears black because all light is sucked into it. For example, you see a chair, it's brown, say, but you see it brown because it appears brown because the light reflected from it is brown. Now, look at the "color" black. It's not a color. It's the absence of light. A black hole is black because it absorbs all light, therefore there is no light reflected from it, therefore there is an absence of light from it, therefore, it appears black. It is black, but it is because it appears so, because it absorbs all light. Therefore, black holes cannot be invisible because then they would be transparent, which means they would let light through. But they absorb it. Slartibartfast1992 16:06, 27 May 2007 (UTC)
replies: text: Yeah, sorry I forgot to sign that.  But I have to disagree with you.  I took issue with the word "appears" because by the definition of the word, one needs to be able to see the object for it to have an appearance.  Beyond the event horizon, one cannot see.  As I said, I may be nitpicking, but I thought it was an important distinction to include in the introduction.  Also, when looking at an object colored black, it is still reflecting some visible light.  If it wasn't, you wouldn't see it.The Great Attractor 00:23, 1 June 2007 (UTC)
replies: text: In principle, you CAN see a black hole.  It is the dark thing between you and the things you can't see hidden behind it. Man with two legs 06:20, 1 June 2007 (UTC)
replies: text: I may be wrong, but I don't think so.  The intense gravitational field of the black hole would bend light from behind it around the hole, leading to distortion, but not necessarily the hypothetical "black" spot appearance. The Great Attractor 01:25, 8 June 2007 (UTC)
thread_title:  Black holes "appear" black? 

message: Hey everyone, what do you think of this picture? Is it worthy of inclusion in the article? No need to answer, just wanted to let you know. Cheers--Cronholm144 17:14, 31 May 2007 (UTC)
thread_title:  picture 

message: As a student in my final year at school, I am extremely interested in black holes and the science behind them. So I have some questions :-
1. Quantum theory says that even vacuum is full of particles and antiparticles annihilating each other. Considering a particular pair, are these particles created because of the energy (due to temperature) at that point in space, or do their own energies add up to 0 regardless of their surroundings?
:Vacuum pair production of virtual particles is a consequence of Heisenberg's uncertainty principle. You can't know the precise energy at a point in space at a precise time. It is possible for the uncertainty in Energy to be large enough to produce a pair of particles, but only if the exists for a short time. The relationship between energy and time is given by \Delta E \Delta t \ge \hbar/2. --Oscar Bravo 12:31, 21 June 2007 (UTC)
replies: text: The treatment is highly mathematical (ie, I don't really understand it :-), but it appears that the infalling particle does indeed have negative mass-energy, with respect to a distant observer (this is important). So its addition to the BH reduces its mass.--Oscar Bravo 12:31, 21 June 2007 (UTC)

text: It can - in theory. The temperature due to Hawking radiation just depends on the mass so a BH with a mass of around 3 x 1019 kg (ie, an asteroid about 100km in diameter) would have a Hawking temperature of about 5,000K and would glow like the Sun. The trouble is that stellar BHs are much larger than this and so glow at very low temperatures. See Hawking radiation for more details and the formula.--Oscar Bravo 12:31, 21 June 2007 (UTC)
replies: text: Light cannot pass through a black hole, but light from behind a black hole can be viewed due to gravitational lensing, if that's what you meant. A spherical object behind a black hole on a direct line of sight to the Earth would appear as a ring shape due to this effect.The Great Attractor 01:21, 8 June 2007 (UTC)
replies: text: Yes, my mistake, that's what I meant. So has gravitational lensing actually been seen or just theorized? Arnavion 09:43, 10 June 2007 (UTC)
replies: text:  It has been observed.  It has been postulated by Atsunori Yonehara at the Center for Computational Physics in Japan that gravitational lensing may be used to measure the mass of supermassive black holes at the center of galaxies, although this technique has not yet been verified. The Great Attractor 02:27, 13 June 2007 (UTC)
thread_title:  Some questions 

message: Okay, what I don't get is how Hawking Radiation works. I understand that particles and antiparticles destroy each other, and that at the event horizon one particle is drawn in and one escapes, giving the appearance of radiation. But it should only be the appearance right? It's not like the particles are coming from the black holes, so how can the black hole lose anything and disappear?
:Easier to understand from the "frozen star" POV: the idealised, extremal end-stage we call black holes is approached but never reached and no event horizon forms to block egress.  The radiation emerging is unruh radiation from the gravitational field -- or equivalently Bremsstrahlung radiation from the infalling matter.--Michael C. Price talk 08:07, 11 June 2007 (UTC)
thread_title:  Hawking Radiation 

message: If Kerr's solution were true, wouldn't that mean that if an object went into a negative gravity universe/reality, the object would undergo some sort of anti-spaghettification and return to its original shape? 87.8.238.123 11:22, 16 June 2007 (UTC)
thread_title:  Anti-Spaghettification 

message: So, do we move this article to Super high gravity locations per the International Space Nomenclature Council's change? Black Holes Renamed 'Super High Gravity Locations' — Jonathan Kovaciny (talk|contribs) 18:46, 22 June 2007 (UTC)
replies: text: No, because we don't have reliable sources.. ;) --Kjoonlee 19:36, 22 June 2007 (UTC)
thread_title:  Super High Gravity Locations 

message: I think the current intro is too long, contains a jumble of unrelated items  and fails to make a clear impression on a reader who is new to the subject. I suggest the intro should cover in as few words as possible: neither light nor the most powerful spaceship can escape; Newtonian mechanics and Einstein's general relativity predict BHs, but only GR explains why the most powerful spaceship can't escape (plus many other features); there appear to be super-massive BHs at the centre of most galaxies.
I think the intro should refer to Newtonian mechanics and its limitations, because many pop science descriptions rely on escape velocity for an explanation, to avoid the complexities and maths of GR.Philcha 12:08, 27 June 2007 (UTC)
thread_title: Introduction