Howard Van Woert

Thanks. What happens when an antimatter black hole collides with a matter black hole? Boom! Boom!

Black bodies and black holes present many analogies with respect to radiation emission: however I think they have different physical nature. What do you think?

Black Holes are very cold and very massive interms of gravity. I suppose all black holes are composed of matter. However, why not have antimatter black holes?

Black bodies is a description of a radiation source. A black hole seems a fine example of a black body. Atoms in a black hole are very cold.

I know that black holes are not the most hot thing in the universe neither the coldest. If you wanna see something really hot (2×10^12 K), try trhis: http://www.physicscentral.com/explore/action/gluon-1.cfm

Is there no Antimatter produced? There is no mention in your blog.

@christopher

You are a little bit outdated

Thanks for the words of wisdom? Maybe I should ask how does the Energy of a Black Hole correspond with Temperature?

Luis Suarez is correct, the answer is very cold indeed. But finitely cold.

But you said that water boils at 100°C. This isn't true in a vacuum. A liquid boils when the vapour pressure of the gas in equilibrium with the liquid equals the external pressure. With 0 external pressure, all the liquid will boil or freeze, with the boiling point of 0K.

Water boils at 100 degrees Centigrade at 1 atmosphere pressure. Is there a place in the universe where the temperature is 0K?

Howard

Don't want to make a mundane conversation in a thread about the temperature of a block hole, however, nowhere is 0K, but in a perfect vacuum there are no liquids at any temperature. It is always above boiling point.

Thanks. The temperature of the Black Hole is inversely proportional to the mass of the Black Hole? Are all the Black Holes ultimately going to vanish?

Yes, all the black holes would radiate their energy away in an otherwise empty university, but even then the lifetime of a black hole of any reasonable size is huge (for a black hole of the size of the Sun it would be 10^67 years; many orders of magnitude larger than the age of the Universe). In addition black holes suck in mass and radiation from the surrounding space, which further prolongs their lifetime.

Then, ultimately 0K shall be reached?

Thanks Tapio!

Howard

It seems to me that Black Holes must be composed of both Ordinary Matter and Dark Matter. Will Dark Matter be turned into Energy like Ordinary Matter by the spinning of Black Holes and the Generation of Hawking Radiation? This will increase the time that it will take for the universe to reach a temperature of 0K.

What do you think Tapio?

The energy in a black hole is definitely very hot because of all the rotating gravitational matter. Also dont forget that black holes do take in entire suns so I would say that along with suns, planets, and other mater including - broken down molecules, atoms, then - protons, electrons, neutrons, then quarks, and other sub atomic particles all being churned around and crushed inside the black hole. This would create a lot of friction and heat as well as pressure.

Diesel engines use pressure to create heat to ignite the diesel fuel so imagine all the pressure and crushing force of gravity inside a black hole with all the matter. This would create very high temperatures indeed same as in suns around the universe.

A black hole is usually formed when a sun burns out and after time collapses in on itself which will create a lot of force just in that action. Suns are very huge indeed and due to their size have a lot of gravity which can pull objects into them. When a sun turns into a black hole it draws in matter and just gets bigger depending on its original size and gravity. Some black holes are massive - very massive and keep growing to frightening proportions.

@Howard. Good questions, but we have no answers at present. We don't know what Dark Matter is (if it exists in the Universe; there are alternate theoretical scenarios that don't need Dark Matter). Coming back to black holes we also don't know what happens after matter is crushed to quarks by gravity, because we don't have a theory for quantum gravity. We can speculate that if black holes had Dark Matter it would be crushed to its fundamental constituents, too (which presumably are not quarks....).

Take my post above as science fiction, with emphasis on *fiction* :-).

Yahia, I guess the name is just a way to emphasize the point that since even light cannot escape from black holes, they behave like perfect (ideal) black body objects in thermodynamics.

Thanks for the discussion. There is a Blog of two chinese physicists who have made a Black Hole from metamaterials. I am not sure what the temperature is of their made Black Hole? It probably depends on the metamaterials used. Maybe just how.

Howard, the metamaterial "Black Hole" has nothing to do with real gravitational black holes. The M-BH is simply a construction to trap electromagnetic radiation (light) by using metamaterials. It's unfortunate that they are using the term Black Hole in this context. It might sound cute but it can cause serious confusion.

If the M-BH is a true black body absorber, it follows the simple black body radiation law and its T is just that of the surroundings.

Thanks. However, could it be the Infamous Dark Matter?

Howard

@Michael, your statement that "the energy in a black hole is definitely very hot" is meaningless (energy does not equal temperature in general). Of course black holes have a huge energy density, but the temperature that you *observe* for them is inversely proportional to mass, i.e. infinitesimally close to T=0 K for massive objects.

@Howard. Dark Matter is (mostly) not "ordinary" (baryonic) matter, metamaterials are, see http://en.wikipedia.org/wiki/Dark_matter.

Does the great gravitational force in a black hole possibly change baryonic matter into Dark Matter?

@Howard, We don't know, because we don't have theory for Dark Matter.

Thanks Tapio!

For me, this question is similar to asking "what is the tangent of 270 ?" is it infinity, minus infinity, both, or none ?

Jose,

I am not sure what you are asking. The original question was about the temperature of a black hole - and that was well answered by Tapio.

Numbers do not have tangents, a tangent is a geometric construction at a point on an object. So a curve in 2D has a tangential line at every point along it.

Thus it is not possible to ask what the tangent of 270 is.

If you can rephrase your question, I am sure that we'll be able to help.

Reading the above comments and some of the literature, I wonder how well established is it that black holes emit radiation as a black body. The latter is a theoretical model for a body that absorbs equally in all frequencies, emits in all frequencies and is at a constant temperature. I can easily see that the first and the third presumptions are plausible, but is the second? Anyone?

@Raphael - Not to poke a hole in your argument out of meanness, but there hasn't ever been an observation of a BH at all. There are mathematical models that assume gravity can "tear a hole in spacetime" to be frank, but this would violate the first law of thermodynamics, and is only a theoretical model. There is still the very real possibility that a singularity is not possible due to some unknown behavior (within microns of where a singularity "could" form, for example). There would be a "center of gravity", but no "singularity". The three assumptions you are making are based expressly on a singularity both existing, and making consistent sense to us compared to everything else.

That said, emission of radiation at every frequency would mean losing a very large amount of energy at higher frequencies, so the singularity would have a finite life span, and "untangle" itself and evaporate. Also, the vacuum is in constant motion (Hawking's virtual pair particles), so it would be beating against the Swarzchild radius of the singularity, causing friction, therefore heat, and charge, and evaporating the BH this way as well. I'm not saying a hardcore center of gravity would be impossible, just that we don't know for sure if spacetime can tear. Hope I'm contributing something XD

@Tapio - dark matter could easily be defined if friction was a field, the same as EM radiation, and the source of mass. All you would have to say then is that friction exists everywhere because motion exists everywhere. Then dark energy becomes heat, and the vacuum temperature of 2.73 degrees Kelvin (WMAP) could be defined as a thermal blanket over the entire universe, due to friction.

@Brandon, please read my comment more carefully. I think you misinterpreted it. First, mine is not an argument, it was a question about the modelling of escape of radiation from black holes. Second, the assumptions I cited are not mine, these are the basic assumptions that constitute the mode called 'black body radiation'. This is a thermodynamic model which is fundamental beyond black holes. While both issues have the word 'black' in them (for obvious reasons) they are independent of one another. Third, the assumptions are not based on any singularity issue. I suggest that you educate yourself on the model of black body radiation. A rather textbook one in thermodynamics. Fourth, the existence or non-existence of black holes was not the issue of my comment. My understanding is that they are inferred from observational data and to my mind this is a pretty strong evidence for their existence. Fifth, the issue of singularity doers not bother me as it should not bother you. Singularities, or more precisely infinities, do not exist in nature! They are only a convenient mathematical limits which often give good approximations of particular model. For example, whether the number of oxygen molecules in the room you are sitting is infinite or just very large does hardly influence the result of the theory that says that you will survive in the room because the oxygens will disperse in it uniformly at some stage. But this is a bit in a tangent to the main discussion here.

Can anyone answer my original question please?

Raphael,

Hawking radiation from a non-rotating uncharged black hole should, I imagine, be radiated in a uniform manner.

A rotating black hole would have a non-spherical event horizon and work has been performed on this topic.

http://arxiv.org/abs/1102.0029

I don't pretend to have read up on this, but it wouldn't surprise me if the spectra of Hawking radiation would differ according to 'location' around the event horizon of a Kerr black hole.

(aha! See abstract - I almost understood it!)

http://www.springerlink.com/content/m42l637v787252v2/

Good question. Thanks.

Thanks Garry for th ereferences.

@Otto. Good point. In the case of a BH we don't know what is the temperature inside (the event horizon), because we don't have a theory for what's in there. The only T that we can define is the one measured from outside of the BH, which is inversely proportional to its mass.

Dear Otto Rössler, you wrote "particle.. can reach the horizon in finite outer.. time..... This assumption, made canonically by Hawking" is this nonsense in his famous paper "Particle creation by black holes"? Please support your statement with reference to a document and page or formula number in it.

It appears that the physical laws of the universe are not the same at BH gravities.

@Otto. Indeed maximally controversial and not exactly a tier-1 publication. To be serious in this business, one needs to do some serious work on quantum gravity.

Agreed, Otto :).

Thanks for the Higgs paper. Otto Good, Basic Physics!

Dear Howard,

Your question has several assumptions, and not knowing your skill level, or reason for asking, I will attempt a layperson answer. That is, I avoid the mathematic equations involved, and relate only concepts, and only a small level of details.

Black holes are a theory based upon General Relativity (GR) and have yet to be proven to exist. But if they do exist and their behavior is accurately predicted by GR and subsequent published and unpublished research, then one must discuss your question in light of it's wording. Particularly the word "in" a black hole.

One must realize that "temperature" as humans experience it, bears no relationship to high speed particles. The word "temperature" must have two definitions, one for human perception and one for science. This area is outside the scope of my answer.

Others have posted about the surface of a black hole temperature, but did not quantity their answer per the size of a black hole, which might be what you are asking about. Small black holes are very hot, spewing particles out very fast, and if the hole is shrinking, its temperature gets hotter and hotter, and it spews out more and faster particles, until it explodes, and the black hole is gone. Large black holes are very cool, even cold, on the surface. Large black holes radiate very little, and what does come out is mostly low speed. I must qualify the above answer to be as predicted by Stephen Hawking and his theory that black holes radiate from the event horizon, according to the theory of "Black Body Radiation." Others have provided some degree of insight and references to such.

The exception to large black hole radiation speed is about in falling matter from the accretion disk being re-directed towards the polar regions and accelerated to tremendous velocities, much faster than anything mankind has ever measured before. Active galaxies appear to have a massive central black hole creating jets of particles going out for hundreds of thousands of light years. They make quasars look weak (black holes whose axis of spin does not match the axis of the jet). But these jets are outside the black hole, thus do not directly related to your question about "in" a black hole.

In response to your question about temperature "in" a black hole, there are two in's, so to speak. There is inside the event horizon, and there is inside the singularity. The "space time" inside the event horizon to the surface of the singularly (which can assume a variety of shapes due to spin and other physics) is "normal" space, just like you and I experience. So, temperature in this volume is "well defined" by the equation relating temperature to kinetic energy, or speed of the particle. If there are no particles in this volume, then there is no temperature. Only particles have temperature, though through Duality waves can be considered particles, and so the qualification of no particles "includes" no waves. If a particle falls in from infinite, then it reaches the escape velocity of the black hole, AT the event horizon, of the speed of light. This particle will have infinite temperature inside the volume under consideration, according to equation that related particle speed to temperature.

Will this particle continue to accelerate once past the black hole, and "exceed" the speed of light, by your understanding? Yes. However, as it's inside the event horizon, and can not be observed from outside, therefore no paradox occurs. So, particles falling in from infinity will exceed the maximum temperature of "infinite temperature." This answer's 'explanation' is outside the scope of my reply.

Low speed particles inside the event horizon will have temperature according to the 'normal' mathematical temperature, and could be even room temperature, or freezing, but not for long, as it's orbit will decay and the particle will enter the singularity volume, and cease to exist, as we know it.

Particles that achieve orbit around the singularity will not have a stable orbit, and will eventually enter the singularity. I read that recently in Scientific American, there are no stable orbits near or inside a black hole, due to twisting of space-time, if the black hole has any rotation, or net charge. Neutral and non spinning black holes, YMMV, I suppose.

So, 'in' a black hole the temperature will average extremely hot, beyond human comprehension, whether the black hole is small or large.

Now, to the last volume of 'space' inside a black hole's event horizon, the singularity. I've quoted 'space' as inside the singularity the word swaps meaning with the word 'time.' That is what you perceive as space-time, has now become time-space. This swap is more a mathematical interpretation, weak at best, imho. Does the word 'temperature' have definition in this 'region?' I do not know. I've not read up on theory in this region, while the theory and mathematics of singularities is an area of interest to me, my other interests have won my time allotment.

Otto,

I feel, like you, that I glossed over the philosophical interpretations of the current state of the art of black hole mathematics. Except, I did qualify at the beginning, that black holes are not 'proven' to exist, if one goes strictly by the book for 'scientific proof.'

The question itself was considered by me to a lay question, as I feel no one with black hole training would ask such a question about temperature "in" a black hole.

So, I laid some basic groundwork, which, yes, left out some (all?) controversial details, just doing the basic, older, interpretation. At least the questioner has some degree of answer, from which they can learn more, as their interest level dictates.

You have clarified for the questioner there is more to black holes than what I wrote, which is a good thing. A very good thing, imho.

What would a person observe falling through the event horizon? In their time frame. The question of the time frame outside the black hole does not seem relevant to the person going through the event horizon. Can 'naked' black holes exist is another question. Just to give the readers some room for other thoughts.

No apology needed, Otto.

Peter

Black holes to have temperature must have massive particles or duality waves. Are not the massive particles in equilibrium with energy. It seems to me that the equilibrium constant of interconversion between mass and energy should be able to be calculated depending on gravity of the system.

Thanks for your insights. Otto

Peter