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Thread: Black Hole FAQ

  1. #451
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    Here is another concise reference that appears to be pretty accurate. As Usual though, one they get to worm holes, they immediately go SciFi!

    http://www.astronomical.org/portal/m...?articleid=141

  2. #452
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    Thumbs up I am new customer of bad forum !

    I hope I will be helpful for all you. I got here because i am interested in astronomy, physics and all close that. I hope our conferences will be friendly and use. Big Hello!

  3. #453
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    I'd like a good, clear explanation of the "negative energy" that's involved in Hawking radiation. I think I have a handle on it, but I feel like I'm on pretty shaky ground.

  4. #454
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    Title: Experimental Evidence of Black Holes
    Authors: Andreas Mueller

    Classical black holes are solutions of the field equations of General Relativity. Many astronomical observations suggest that black holes really exist in nature. However, an unambiguous proof for their existence is still lacking. Neither event horizon nor intrinsic curvature singularity have been observed by means of astronomical techniques. This paper introduces to particular features of black holes. Then, we give a synopsis on current astronomical techniques to detect black holes. Further methods are outlined that will become important in the near future. For the first time, the zoo of black hole detection techniques is completely presented and classified into kinematical, spectro-relativistic, accretive, eruptive, obscurative, aberrative, temporal, and gravitational-wave induced verification methods. Principal and technical obstacles avoid undoubtfully proving black hole existence. We critically discuss alternatives to the black hole. However, classical rotating Kerr black holes are still the best theoretical model to explain astronomical observations.

    Read more (2078kb, PDF)

  5. #455
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    What is the relationship between time and a black hole? Since gravity slows time down, it would stand to reason that the strongest gravitational force possible in the universe would stop time altogether. Could this be part of the reason behind the very strange behavior that we see in BHs - that time is frozen? Also, could a very, very massive black hole actually turn time backwards?

    How does a black hole become larger or "more massive" if the singularity is mostly composed of energy? Is this a case of energy displaying characteristics of gravity?

    Does a black hole ever explode? I've heard that they might "fizzle out" or evaporate. What would this look like...a gradual process, or a spectacular explosion?

    Could evaporated black holes be responsible for some of this "dark matter matrix" that holds the Universe together that we're seeing just recently?

    Can an artificial black hole be stabilized in the lab? If it could, could it be used to do anything useful? Should we try, or is this way too dangerous?

  6. #456
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    Quote Originally Posted by sechen View Post
    What is the relationship between time and a black hole? Since gravity slows time down, it would stand to reason that the strongest gravitational force possible in the universe would stop time altogether. Could this be part of the reason behind the very strange behavior that we see in BHs - that time is frozen?
    Yes, that is the normal view of an event horizon-- a place where time is frozen by gravity. Of course this only holds in the frame of reference arbitrarily far from the black hole. If you are flying across the event horizon, time flows normally. It's a part of relativity-- time flows differently in different reference frames, and in general relativity, being at a different place in a gravitational well can itself be viewed as a different reference frame.
    How does a black hole become larger or "more massive" if the singularity is mostly composed of energy? Is this a case of energy displaying characteristics of gravity?
    Energy always displays the characteristics of gravity-- gravity doesn't really distinguish those concepts.
    Does a black hole ever explode? I've heard that they might "fizzle out" or evaporate. What would this look like...a gradual process, or a spectacular explosion?
    This sounds like "Hawking radiation", a very esoteric speculation that if true, means very small black holes evaporate very quickly and very brightly, but "normal" sized black holes are not really affected in any significant way.

    Could evaporated black holes be responsible for some of this "dark matter matrix" that holds the Universe together that we're seeing just recently?
    No, we'd see the results of evaporated black holes. Dark matter is something different.
    Can an artificial black hole be stabilized in the lab? If it could, could it be used to do anything useful? Should we try, or is this way too dangerous?
    The only way we currently know of to make a black hole requires more than the mass of the Sun. Can you fit that in a lab? Note that if there were a way to make much smaller black holes, they would still have no different gravity if you were a few inches away from them than that amount of matter does now. You'd have to venture extremely close for the gravity to do anything important, and we can already make things that are very energetic when you get that close (like nuclear reactions). I really don't see black holes as a laboratory phenomenon, but some people are trying. No, there is no particular danger in this effort, futile though it probably is, because there is no evidence for any "chain reaction" of the type that makes nuclear material so dangerous.

  7. #457
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    Does Dark matter get captured by a black hole?

  8. 2007-Jan-19, 10:15 PM

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  9. #458
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    black holes

    my 1st submission. since string theory became popular, i've seen more talk about membranes. when 2 membranes composed of dark energy or matter came into contact, what if they caused creation of a vortex. i'm using creation of tornados in weather on earth as a parallel. ie a cold front and a warm front. the creation of these vortexs in a universe of dark energy and or dark matter, would be the beginning of a black hole. as its spinning increases, perhaps this would serve as a factory from which matter, as we know it, would be created from the high speed and intense heat stemming from the dark matter points interacting and colliding with each other. from this interaction would come the creation of the galaxy around the black hole. this is the 1st time i've typed anything about this subject. but, one of the things i'm getting at is this might be a, "what came 1st, the chicken or the egg?" perhaps there's a process where the black hole was 1st causing creation of the galaxy afterwards. most of the universe is thought to be made of dark energy or matter, but i don't think its influence has been considered in proportion to its seeming prominence.

  10. #459
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    Quote Originally Posted by transreality View Post
    Does Dark matter get captured by a black hole?
    Yes, dark matter is subject to large-scale gravitational instability (though not the small-scale instabilities that make stars, that requires radiating light), and so should contract into supermassive black holes the same way normal matter does. Unfortunately, it's not even perfectly understood how normal matter gets into supermassive black holes!

  11. #460
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    Quote Originally Posted by traintaz View Post
    i'm using creation of tornados in weather on earth as a parallel. ie a cold front and a warm front. the creation of these vortexs in a universe of dark energy and or dark matter, would be the beginning of a black hole. as its spinning increases, perhaps this would serve as a factory from which matter, as we know it, would be created from the high speed and intense heat stemming from the dark matter points interacting and colliding with each other.
    I've never heard the idea that normal matter might spring from dark matter interactions, because the Big Bang theory has a pretty natural way to generate the normal matter we see. But until we know more about dark matter, I suppose anything is possible, and all ideas should be on the table.

    perhaps there's a process where the black hole was 1st causing creation of the galaxy afterwards.
    Evidence is growing that supermassive black holes and galaxies form together in a kind of dance with unknown steps, but it would be hard to get the matter from the black hole because most of the normal matter in the universe is not in galaxies but rather between galaxies in clusters, yet the matter seems pretty similar (so far as I know) in those two places. If evidence could be found that the normal matter between galaxies was much different than the matter in galaxies, this would be quite an interesting way to consider that. I suppose you could also have galaxies "evaporating", but the physics of that might not work out. It is certainly an interesting idea to consider, especially if the current view cannot succeed in explaining the newest data coming in.
    most of the universe is thought to be made of dark energy or matter, but i don't think its influence has been considered in proportion to its seeming prominence.
    That may be true. It could just be a bias that dark matter is felt only via its gravity. Current expectations are that it won't be possible to turn dark matter into normal matter, they are just different families of stuff, but I'm not a particle physicist, and even if I were, I could be wrong anyway.

  12. #461
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    i'm afraid i'm not 100 percent behind the big bang. i've seen the images of black holes exhausting xrays at super hi speeds and temperatures as high as 5 million degrees c. i'm just supposing this exhaust would have a significant influence in the universe. hi speed and hi temps are the catalysts for the creation in stars, of different elements and semi conductors, muons and other as yet undiscovered particles. i just feel that black holes are not just destroyers, but creators as well. creation from destruction just may be conversion. i enjoy getting perspective on my ideas, but this is my 1st time doing this discussing on a forum, but i don't mind finding out that i'm wrong!

  13. #462
    ^^ thats how i envision black holes, the x - rays & temps being exhausted like solar flares on a much larger scale must have some effect on the creation or catalysts the process of new entities in space, much like a flower pod being blown in the wind.

    Just to clarify some quarrels i have about black holes.
    So, they form when the density of the planet becomes so great that it collapses, when it collapses gravity becomes more and more and the electrons are compressed to such a tight space that they are bouncing so fast off each other that it approaches the speed of or close to the speed of light thus tearing a hole in space as we know it.

    now tidal waves are some thing that intrigues me aswell, now I understand that space is 3 dimensional , but the fact that they bend the space around them seems quite amazing to me, being contorted like their graphical representations.
    Is it possible for black holes to spin? like what would happen there? would the black hole suck in the bend in tidal waves like wrapping something up?

    cheerz.

  14. #463
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    Black holes have nothing to do with planets. They are formed when very massive stars (more than 8 times the mass of the Sun) run out of fuel. The core collapses to a black hole and the rest explodes as a supernova.

    Yes black holes can (and probally do) spin. The (only) three attributes of a BH are mass, charge and spin. What you are describing is "frame dragging". There is a satellite in orbit now (Gravity Probe B) that is designed to measure the frame dragging of the Earth.

  15. #464
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    Quote Originally Posted by traintaz View Post
    i just feel that black holes are not just destroyers, but creators as well. creation from destruction just may be conversion. i enjoy getting perspective on my ideas, but this is my 1st time doing this discussing on a forum, but i don't mind finding out that i'm wrong!
    You're not wrong that black holes affect their environment, as do the supernovae that created them. But all of this is being accounted for in modern astronomy. The effects of the pictures you are talking about are measured and included in the ecology of a galaxy. It's not going to replace the Big Bang, unless we have a lot of things pretty majorly wrong. Wouldn't be the first time, but the evidence that you need the Big Bang to accomodate all the data is pretty overwhelming.

  16. #465
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    Quote Originally Posted by sechen View Post
    What is the relationship between time and a black hole? Since gravity slows time down, it would stand to reason that the strongest gravitational force possible in the universe would stop time altogether. Could this be part of the reason behind the very strange behavior that we see in BHs - that time is frozen?
    Here is another way to look at the event horizon:

    Matter in orbit around a massive body cannot fall in without losing energy/angular momentum. This is why the earth does not fall into the sun: it has no way to lose its potential energy with respect to the sun, nor its angular momentum.

    Hot gas around a BH, however, does have a way to lose energy: radiation. Thus, as matter nears the BH, it gets hotter and hotter, radiating away more and more energy, spiralling ever closer to the event horizon.

    Once it gets to the event horizon, however, it can no longer radiate away energy, because gravity will not let radiation escape. So we arrive at a paradox: matter must lose energy to cross the event horizon, but the event horizon will not allow such loss to occur.

    If we watched the BH forever, of course, the radiation would eventually escape, but without such patience, we will never see it. Since we do not see the radiation escape, neither do we see the matter fall in. It is not so much that "time is frozen" at the event horizon; rather, information about what is happening at the event horizon "gets stuck."

  17. #466
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    what do i know about a black hole for sure? it spins and pulls stuff into it. the stuff that gets pulled into it becomes compacted until it reaches a point called the singularity. i assume, at that point, it then begins projecting the jets of energy that are depicted in the illustrations i've seen. the "stuff" doesn't get erased then, its form is just changed. you've got speed, you've got heat, you've got a factory! as the black hole gets more and more massive do you then get a bigger or more denser singularity? does the singularity have a critical mass that when reached, then begins the ejection process.

  18. #467
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    Relativistic jets do not come out of the black hole. The jets are accretion disk material (outside of the Schwartzchild radius) that is accellerated to high speed speed (near c) and focussed by the magnetic field of the black hole.

    The singularity is just that - zrero radius, zero volume, infinite density. As the black hole gets more massive, the singularity does get larger - zero + x = zero, but event horizon does.

  19. #468
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    the high resolution radiao pictures of black hole jets belong surely to the most Amazing stuff of all astronomy ...

  20. #469
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    HOLY HALEAKALA!

    I totally forgot about this thread. My face is so red it's at a z of 10.

    We developed the Black Hole Fact Sheet some time ago, and we wound up having to base it on some assessments done at museums and such. The questions and answers asked here were of great help at the onset, so I thank everyone who helped!

    The Fact Sheet is actually online: Full color version or Greyscale version (for printing). We even have Spanish versions too (color, and greyscale).

  21. #470
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    Oh-- I'll unsticky this, too.

  22. #471
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    Maybe this was asked...

    If two identical super-massive black holes moved close enough to each other... would they be able to suck matter from each other? Or Would they simply coalesce?

  23. #472
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    Quote Originally Posted by EvilEye View Post
    Maybe this was asked...

    If two identical super-massive black holes moved close enough to each other... would they be able to suck matter from each other? Or Would they simply coalesce?
    They would merge. Here is an (older) but still good explanation as to what would actually happen, and probably will with this specific example.

    Link

  24. #473
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    Black Hole Questions

    Following up on this comment:

    Not just possible. There is evidence for some SMBHs being near 1010 solar masses. NGC 1459 has one that's 2.5 billion.
    How could such a large black hole form? Where is the matter source? Galactic collisions? How many are required in 14 billion years?

    When in the standard cosmological model, did black holes start to form?

    Black holes are a theoretical interpretation based on an extrapolation of GR. Is there observational evidence that supports that the massive objects are “black holes” in the GR sense or could they be some other neutron like massive object? Is charge conserved in a black hole? i.e. Does charge conversion occur in a black hole?

    Say for example Granolaeater’s comment:

    There is indeed a theory that there is a next degeneracy threshold beyond neutron matter called quark matter. But such a hypothetical quark star would be more like a superdense neutron star then a black hole. It would have a surface just like a neutron star. This means that infalling matter would create X-ray Bremsstrahlung. In Black holes there is no Bremsstrahlung because there is no surface. In black holes spacetime is so much distorted that matter looses all its properties expect mass, momentum and rotational momentum.
    Comment:
    I have the same questions as asked above concerning charged and uncharged, rapidly spinning black holes. Does a rapidly charged black hole radiate?

  25. #474
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    Quote Originally Posted by tngolfplayer View Post
    I am interested in knowing how far the gravity from a black hole extends, what the suppossed size of the one in the center of the Milky way is, and how different types of stars become black holes.
    Thanks.
    Wouldn't you say this varies with the size of any givin blackhole?

    EDIT: There are known characteristics of stars that are more likely to turn into blackholes. Like our sun, is not likely to turn into one, it simply isn't massful enough.

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