Talk:Black hole

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Black Hole Emitting Light?

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)

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)

Irony in the article

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)ninetigerr

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)

Colonize Black Holes

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)

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)

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)

So will a distant observer (ie us here on earth) ever see a black hole form

Sorry to go back to this old chestnut, as it seems to have been siezed upon by an editor with lots of "interesting" ideas. But i have come across this problem before, and never had it satisfactorily debunked. I'm going to phrase it carefully: Given an arbitrarily long but finite amount of time (distant observer's local time) will a distant observer ever see a star become a black hole. Time dilation during gravitational collapse suggests not.--Mongreilf 14:00, 30 November 2006 (UTC)

Define "see".

The problem with question is that -- strictly speaking -- we cannot know whether or not something is a black hole until the infinitely far in the future. (See Hawking & Ellis' The large-scale structure of spacetime, or Thorne's Black Holes and Time Warps.) A black hole is defined as a region from which nothing can ever escape. We can't know if anything ever escapes until we know everything that ever happens. In this sense: no, we can never "see" a black hole form.

Now, Physics is more or less the science of predicting what will happen, given some knowledge of the present state of the Universe. In this case, we measure a certain amount of mass (for instance, by watching stars in orbit around the mass), and the size of the space it fills up. If it is smaller than a certain size, General Relativity predicts that nothing will ever escape. In this sense, we can deduce that a black hole exists. Any time astronomers talk about "seeing" a black hole, this is basically what they mean. (Of course, General Relativity might actually be wrong...)

Personally, I think this is sufficiently well explained in the Evidence section. On the other hand, I'm not the target audience. If you have any ideas on how to make it clearer, please share. --MOBle 19:33, 2 December 2006 (UTC)

see as in a distant observer looking at a warm collapsing remnant star, emmiting radiation (though horribly red shifted), then later no longer emmitting anything due to the escape velocity exceeding light. and i mean in a GR model of this situation, rather than reality. all from the point of view of the distant observer —The preceding unsigned comment was added by Mongreilf (talk • contribs) 13:06, 3 December 2006 (UTC).

(Well, that's not really the definition of a black hole, but...) Okay, so now we can ask if it is ever possible to see something go so dim that it stops emitting anything -- like a photon. Presumably, if it ever does grow so dim, there is some last photon emitted. How can we possibly decide if we've seen the last photon? I maintain that we can't, unless we know everything that will ever happen, or use Physics to predict everything that will ever happen. This is the same answer as above.

I write this only in the hopes of clarifying my previous comment with a helpful analogy. As noted, the definition of a black hole does not involve dimness or escape velocity. --MOBle 23:05, 3 December 2006 (UTC)

yes, fair enough about the last photon, but presumably we are able to model and extrapolate a decline in photons and use a lack of photons received as statistical evidence that such a model is good. very little science is based on "total information". also i must be very old school, i thought escape velocity > light speed was one of the definitions of a black hole.--Mongreilf 12:21, 4 December 2006 (UTC)

Regarding the "model", this is just what I mean by "use Physics to predict everything that will ever happen". I agree that very little science is based on "total information", but this is precisely the unusual feature of the definition of a black hole; it is both a strength (in the sense that it allows us to prove interesting mathematical theorems and a weakness (in the sense that it requires a knowledge of the future of the Universe). If I recall correctly, Hawking's decision to use this "teleological" definition is insightfully narrated in Thorne's book.

The currently accepted definition is this one that basically involves an (absolute) event horizon. The original notion did use the somewhat weaker apparent horizon, which sort of boils down to "escape velocity" > speed of light. This is also the heuristic definition, but it is not exactly correct. --MOBle 22:56, 4 December 2006 (UTC)

Mass of black holes

On the main page about black holes at the beginning where it mentions the masses expected for black holes, it has been suggested in J-P Luminent's "Black Holes" (Cambridge press, (c)1992)(its an older book but its points are still valid), that it is possible to have a black hole of any mass if its contents are compressed sufficiently. In the book he mentions that a black hole could form when a mass the size of a mountain, is compressed down to a small Tv, which is significantly less massive than the mentioned sizes predicted on the main page. Additionally, the next generation of particle accelerators are predicted that they may even be able to create micro miniature black holes with lifetimes in tiny fractions of seconds, as was suggested by a fairly recent poplar science article. Chris2746 07:55, 3 December 2006 (UTC)

It is true that a black hole could have (basically) any mass. Rock weighs about 2700 kilograms per cubic meter. I guesstimate that a mountain might weigh 10¹³ kg. In geometrized units, this is 10^-14 meters. (Google calculation) Multiply by two to get the size of the black hole, and you get something the size of a proton. That's a pretty small TV. Conclusion: Luminent was either wrong or talking about something else. One way to find out is to look for another source. The particle accelerator issue was dealt with above. --MOBle 23:05, 3 December 2006 (UTC)

"Simple Overview"

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).

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)

Black Hole: Destructive Force or Life Builder

Black Hole Theories:

For all my adult life I have wondered if our understanding of Black Holes have been flawed. It is taught in grade school and even our colleges around the world that Black Holes destroy everything in there paths, this belief is from only looking at similar occorances here on earth, such as, Hurricanes & Tornados. While it is a common understanding that these earthly forces do have a path of destruction, does it always mean that all aspects of occurances throughout the universe having the same appearance as those on earth, make them a destructive force?

In science we have been taught to look at all the aspects of what is not understood so that we can conclude a new understanding. So, how about this aspect of Black Holes, Life Builder.

As we look into the the heavens and admire the shear beauty of the universe we find one specific denominator, what is it? Well, it's not the darkness. It's not the great number of lights. It's not the shear number of galaxies or planets that inhabit the galaxies. Actually it is one thing that 99.99% of all human see everytime that we see the moon in the night sky or pictures of our beautiful planet that we call home. The one common denominator is in fact that not only as with the earth and the moon, every planet that we see in pictures are "ROUND" not square or mashed together but "ROUND".

We have been taught that matter and light do not escape the gravitational forces of a Black Hole and that once caught in the clutches of the event horizon, all life as we know it is doomed for destruction and out of existance. It is my belief that this teaching and understanding is flawed.

As with the mining of minerals from beneath the surface of our planet earth and mingling it with fire and other minerals transforms Iron Ore into steel, it would not be far fecthed to believe that Black Holes do the same thing and with the same type of results with the creation of life in the form of "ROUND" Planets.

If we look at the event horizon of a Black Hole we would notice not only light but also debris in the form of astroids and whatever else was caught up in the outer bands of this massive looking storm. With all these particles being directed to the center of the Black Hole, this debris would be compressed into a molten ball eventually being redeposited into the vastness of space. Towards the end of the life of the Black Hole and one the deposits of debris begin to run out, this may very well be where each Solar System is born into existance with a new sun. As with our own Sun, we do know that it has a strong gravitation pull on all the planets that surround it along with debris fields known as the Milkey Way, revolve around that center focus.

I pose this one Question: Could it be that our Sun as we know it, is the actual reminants of a Black Hole, burning off the last remaining particles of light and debris resulting in the heat and light that nurtures the life on the surface of our planet that we call home? Jdsparks 20:04, 10 December 2006 (UTC)

To answer your questions briefly (a more detailed answer might be obtained by asking on the Wikipedia science reference desk:

1. The sense in which black holes "destroy" everything is, that an object which gets too close to one, will be unable to escape, and will ultimately suffer destruction molecule by molecule through spaghettification, due to the extreme forces of gravity operating within a black hole. That should count as "destruction" in any book, at least as far as those living where it came from are concerned. See the Simple Overview section of this article for more.
2. The description is nothing to do with earthly weather, and everything to do with what happens when you put a finite mass in a relatively tiny amount of space until it collapses under the force of gravity, and then travel too close to it.
3. Whilst it is possible that in some ways black holes build and create "life", in whatever form that might mean, we have no evidence of it now. Wikipedia is not a crystal ball, and we do not put ideas in here that aren't verifiable (or at least whose credible and noteworthy proposal is verifiable) in the real world somehow. This is (at the moment at least) just speculation, and we don't put our own ideas in Wikipedia, however attracted we might feel towards them, but only things which seem to have some kind of notable support or the like.
4. The reason things are (roughly) round is similar to the reason that the oceans and your glass of water are (roughly) flat. There's no great mystery to it. Gravity attracts matter equally in all directions, and the shape which a centrally directed and rotationally symmetrical force tends to create is a sphere (in 3 dimensions) or a circle (in two).
5. Your belief may well be interesting for you. But it wouldn't get into encyclopedia brittanica or any other encyclopedia, because it isn't shared by those who have experience of such things. You might find this page WP:OR on personal views and beliefs, useful.
6. A black hole is not going to create a ball of some kind at the centre, molten or otherwise. The centre of a black hole is a point, known as a singularity, and any object sufficiently close to it will be shredded into pieces, then the pieces into atoms, then the atoms into subatomic particles, and into the zero size point that is the singularity. There's no solid object in the middle for planetary formation, the gravitational field would be too strong for that to exist.
7. The Milky Way doesn't lie around the sun and isn't a debris field of any kind. In fact the sun is close to the edge, in one of the spiral arms of the Milky Way galaxy, nothing to do with the centre.
8. Last question, no it couldnt be. A black hole is simply a black hole, they don't have "remnants" that "burn off last particles". You might be thinking of other forms of star, but a black hole is not that. It isn't "burning" anything. It's collapsing into zero space, due to the incredibly high gravitational field it creates in its immediate vicinity.

Hope this helps. FT2 ^{(Talk | email)} 21:40, 10 December 2006 (UTC)

Table?

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
	J = 0	J ≠ 0
Q = 0	Schwarzschild	Kerr
Q ≠ 0	Reissner-Nordström	Kerr-Newman

FT2 ^{(Talk | email)} 02:13, 11 December 2006 (UTC)

nearest candidates

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)

Black holes in fiction?

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)

I say go ahead and start such an article if you are inclined. I'm not sure it would be appropriate to have a section in this article on that topic. Such a section is liable to get too large and distract from the scientific focus of this article. A link from here to the BH in fiction article would be appropriate, however. -Joshua Davis 22:16, 21 December 2006 (UTC)

Now added. --GwydionM 17:56, 23 December 2006 (UTC)

GA failed

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)

Bad section

The section Event horizon is incorrect. It states that nothing can escape a black hole because the escape velocity is greater than the speed of light. This is an old, incorrect, non-relativistic explanation of a black hole. The real reason that nothing can escape a black hole is that space-time is curved due to gravity and only an inward direction remains. Berrick (talk) 11:31, 10 January 2007 (UTC)

• Can you provide a reference? Given the kind of metrics used inside black holes, I'm not sure what your saying is a good presentation without backup explainations for laymen. WilyD 14:15, 10 January 2007 (UTC)

Until this is fixed, I've patched the intro to remove the technical reason (whether escape velocity or curvature) and in doing this, tried to make it more helpful, for example by explaining the observation is impossible for the same reason. FT2 ^{(Talk | email)} 17:49, 10 January 2007 (UTC)