#21
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In article , "Richard D. Saam"
writes: On 6/9/13 5:55 AM, Phillip Helbig---undress to reply wrote: No. The new phases involve MOLECULAR hydrogen. Yes, MOLECULAR hydrogen but possibly in a phase not presently electromagnetically observable a la 'dark matter' a portion of which continues to sublimate into presently electromagnetically observable gaseous MOLECULAR hydrogen. Work through big-bang nucleosynthesis, include this new phase, and let me know what you get. |
#22
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On 6/4/2013 1:24 AM, Robert L. Oldershaw wrote:
Beware glib answers. Science requires much more thought and skepticism. What does the math say, if anything, about black hole mass? or perhaps a better way to put this is "what is responsible for black hole mass"? [Mod. note: quoted text trimmed -- mjh] |
#23
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Op zaterdag 15 juni 2013 08:09:00 UTC+2 schreef David Staup het volgende:
What does the math say, if anything, about black hole mass? or perhaps a better way to put this is "what is responsible for black hole mass"? I think to answer the question "What is responsible for mass" is impossible. On the other hand to answer the question: "how do we calculate the mass of the blackhole" please read this http://www.eso.org/public/news/eso0846/ Specific follow the first link "More Information" An other good document is this: http://en.wikipedia.org/wiki/Sagittarius_A* Nicolaas Vroom |
#24
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On 6/17/2013 2:21 AM, Nicolaas Vroom wrote:
Op zaterdag 15 juni 2013 08:09:00 UTC+2 schreef David Staup het volgende: What does the math say, if anything, about black hole mass? or perhaps a better way to put this is "what is responsible for black hole mass"? I think to answer the question "What is responsible for mass" is impossible. My question was specific to black hole mass and I meant the question to point out that "we" cannot describe the source of a black hole's gravity. Is it matter, dark or otherwise? Is it energy? Or is it something else? [Mod. note: not sure what you're getting at here. 'The math' (i.e. relativity theory) says that black holes are a form of matter, and therefore of energy. Whether they are 'dark' or not in the astronomers' sense depends on their environment -- mjh] |
#25
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In article ,
David Staup writes: Whether [black holes] are 'dark' or not in the astronomers' sense depends on their environment -- mjh] Whether they are radiating or not depends on the environment. The OP's language was confusing, but I think his "dark or not" might have been meant as "baryonic or not." That depends on the formation process. All processes we know of for making black holes involve baryonic matter, but in principle non-baryonic matter could form black holes if there were some way to concentrate it enough. Existing black holes must accrete tiny amounts of non-baryonic matter regardless of how they formed. Black holes are, so far as we know, a trivial part of even the baryonic mass of the Universe, so the data don't support worrying about a non-baryonic component. Theory could deal with the consequences of non-baryonic black holes if that turned out to be important. -- Help keep our newsgroup healthy; please don't feed the trolls. Steve Willner Phone 617-495-7123 Cambridge, MA 02138 USA |
#26
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Le 17/06/13 21:04, David Staup a écrit :
My question was specific to black hole mass and I meant the question to point out that "we" cannot describe the source of a black hole's gravity. Is it matter, dark or otherwise? Is it energy? Or is it something else? [Mod. note: not sure what you're getting at here. 'The math' (i.e. relativity theory) says that black holes are a form of matter, and therefore of energy. Whether they are 'dark' or not in the astronomers' sense depends on their environment -- mjh] Is the ratio dark/visible matter in the galaxy known? If yes, then we should expect that same ratio in the central black hole of the galaxy isn't it? If that mass is "X" kg, a certain percentage of it (the same as the galaxy as a whole) should be dark matter. Since nothing gets out of that hole (it is completely invisible), in principle knowing if that ratio holds is impossible. Or is 100% of the mass of a black hole "dark" matter? Black holes are... black!!, the color of darkness :-) Black hole mass has some characteristics of dark matter. It only interacts with the rest of matter through gravity. A "black hole" particle would fit our WIMPY thoughts or not? Black holes much smaller than the size of an atom *could* exist and even in big numbers. Problem is (for my new theory of the universe) that holes tend to slowly fill with surrounding matter that falls into them. If atomic black holes interact with atoms by swallowing them, they should be visible after a certain time has passed since they would get bigger and bigger. And when swallowing an atom it is difficult to believe that not a single photon (gamma ray, whatever) would not be emitted. What is not detected. And there it goes, my new theory of the Universe... |
#27
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In article ,
jacob navia writes: Is the ratio dark/visible matter in the galaxy known? Not as well as we might like. It's hard to measure either one from our location within the Galaxy. Values for external galaxies thought to be similar to the Milky are better known. If yes, then we should expect that same ratio in the central black hole of the galaxy isn't it? Why would you expect the average ratio for the whole galaxy to apply to any specific region? An average is even less likely to apply to a region that has special conditions. If that mass is "X" kg, a certain percentage of it (the same as the galaxy as a whole) should be dark matter. Are you using "dark matter" as a synonym for "non-baryonic matter?" They aren't the same. For obvious physical reasons, a black hole is far more likely to accrete baryonic matter than non-baryonic matter. Or is 100% of the mass of a black hole "dark" matter? This is a question of terminology. Isolated black holes are "dark matter" (but within the baryonic mass budget), but accreting black holes are not dark. However, they contribute a trivial fraction of the overall mass budget of a galaxy. Nevertheless, a black hole's mass can dominate its immediate surroundings. Black hole mass has some characteristics of dark matter. It only interacts with the rest of matter through gravity. Black holes can be charged, though there's no evidence that real ones are. A "black hole" particle would fit our WIMPY thoughts or not? Absence of lensing rules out stellar-mass and larger black holes as significant components of dark matter. And anyway black holes would be baryonic and would not contribute to the non-baryonic dark matter. Black holes much smaller than the size of an atom *could* exist and even in big numbers. You might want to calculate the lifetime of such a black hole. That's aside from the lack of any obvious creation mechanism. -- Help keep our newsgroup healthy; please don't feed the trolls. Steve Willner Phone 617-495-7123 Cambridge, MA 02138 USA |
#28
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Le 20/06/13 08:36, Steve Willner a écrit :
Why would you expect the average ratio for the whole galaxy to apply to any specific region? An average is even less likely to apply to a region that has special conditions. I suppose that this "dark" matter interacts with matter through gravity. A black hole is quite a beast in gravity terms. It is a very strong gravity field isn't it? Then it should attract as much "dark" matter as normal matter and should feed with BOTH kinds of matter. Interestingly, does that "dark" matter emit any kind of radiation when leaving this world into the black hole? Observing the black hole at the center of our galaxy if we detect some radiation with no obvious normal matter to explain it, it could give us (yet another) test for that "dark" matter, unless it emits "dark" photons :-) jacob |
#29
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On Thursday, June 20, 2013 2:36:31 AM UTC-4, Steve Willner wrote:
In article , This is a question of terminology. Isolated black holes are "dark matter" (but within the baryonic mass budget), but accreting black holes are not dark. However, they contribute a trivial fraction of -------------------------------------------------------- An important correction here is that primordial black holes, i.e., black holes that are not formed in supernovae, are non-baryonic and do not come "within the baryonic mass budget". |
#30
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Le 31/05/13 08:03, Richard D. Saam a écrit :
There are no (within 95% CL) WIMP annihilation cross sections and decay lifetimes as measured by FERMI LAT that could contribute to dark matter. http://arxiv.org/abs/1305.5597 Frustrated by dark matter? Can't figure it out? Do not worry. YOU ARE NOT ALONE. Read this article written by the famous scientist "Lord Kelvin" (Sir William Thomson ) in Macmillan's Magazine, vol. 5 (March 5, 1862), pp. 388-393. In this article Lord Kelvin tries to figure out how old the sun is. His only conceptual framework to explain the heat of the sun was that this heat was "generated by the falling in of meteors" But that provokes OTHER problems since in their way to the sun those meteors should pass through the earth orbit... The url for that document is: http://zapatopi.net/kelvin/papers/on...suns_heat.html It makes for a fascinating reading, hopefully the same kind of fascination that astronomers in year 2163 will have when reading the discussions here or the papers about that mysterious dark matter. |
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