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Black holes

  1. Aug 28, 2003 #1

    wolram

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    it seems that the existence of black holes is taken for granted
    thees days, but there are people who question there existence,
    under the heading "binary star", in this forum, john shoemaker
    proposed a theory that would disprove black holes.
    this has me thinking "what is the evidence for black holes"?
    is the evidence for there existence irifutable, or is there
    still room for debate?
    best wishes..
     
  2. jcsd
  3. Aug 28, 2003 #2
    I am not an expert, but I believe black holes are an expected consequence of the star gravitational collapse when a certain Mass/Radius (Oppenheimer?) limit is surpassed.

    I think this conclusion is demonstrated at the Hawking-Penrose theorems, assuming certain reasonable points.

    But, experimentally, I believe exist strong traces but not definitive data. Probably some other user could inform us about the state of the experimental search.
     
  4. Aug 28, 2003 #3

    marcus

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    this is a good question, and Curro Jimenez comments

    "But, experimentally, I believe exist strong traces but not definitive data. Probably some other user could inform us about the state of the experimental search."

    there is a bunch of observational evidence, and several people here (Phobos, Labguy, chroot, J-man, .....others) could summarize it for us

    I was very impressed this year by an ESO observation of what seems to be a several million solar mass BH at the center of our galaxy

    they watched a star do a highly elliptical orbit that came very close to the focal point----within light-hours!!!!

    they could tell the mass of the object, from the star's orbit and they could tell it was very small (because of how close the star came)
    so they calculated and considered all the possible explanations they could think of and excluded them one by one (it was some Frenchmen in Paris analyzing the data) with extreme care and they found no other physical explanation except that there was a BH of that mass and that size at the center of MilkyWay

    nothing is irrefutable

    but every year people find more and more evidence, keep observing more and more things that are most conveniently explained by there being a black hole.

    also some galaxy was observed to have two black holes as i recall.

    the concept is used to explain so many things----formation of galaxies, power of quasars, cause of gammaray bursts, X-ray sources. certain kinds of jets and radio sources.

    maybe we can get someone to weigh in who has the information
    together and even some links

    woah! I seem to remember that an accretion disk has actually been observed. is this possible

    but nothing is irrefutable, all conclusions are at best "beyond reasonable doubt" and ultimately rest on the subjective judgement of the herd---how else can it be?
     
  5. Aug 28, 2003 #4

    wolram

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    hi marcus,
    do you give any weight to the gravstar theory?
    also may i reffer to john shoemakers theory under the
    binary star thread.
    the entropy of a BH has been discused in this forum
    before, the thing that puzzles me is why the loss
    of information is so important?
    in my oppinion BHs are a wart on cosmology, something one
    wants to get rid of but always comes back.
    best wishes..
     
  6. Aug 28, 2003 #5

    wolram

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  7. Aug 28, 2003 #6

    marcus

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    Hi wolram,

    I had a brief look at the page you linked to and it seemed to me the author was quarreling with the "singularity" (and in particular the infinite density) notion

    I counted 20 or so occurrences of the word "singularity" until I gave up counting------sort of once every two sentences or 5-10 times a paragraph.

    He seems to think it would be alright if the mass of the sun were packed into a 3 kilometer radius ball

    (observationally that is what I would call a black hole, any mass contained within its schw. radius-----I dont care what happens inside the event horizon that is the holes own private business)

    he seems to think that would be OK because there is no claim of "singularity" or "infinite density", you just have a certain mass confined within its schw. radius

    formula 2GM/c2, which in sun's case is 3 km.

    What about this?

    Let's chuck the idea of "singularity" since it refers to a breakdown of a particular theory----a limit to applicability of GR inside the event horizon

    Let's all agree that these objects exist---that they are being observed by the hundreds---that interesting stuff goes on around them which agrees with the GR model

    the GR model works fine OUTSIDE the event horizon and all kinds of interesting fireworks happens right outside (because of stuff falling in and getting very hot as it falls in) which is exactly as predicted.

    these things power quasars that we have been observing since what the Nineteen Fifties?

    a lot of these things are big-----100 million solar masses---and they act just as GR says a black hole ought to act---and a lot of astronomy depends on quasars since they are among the most distant stuff we can see. So Black Holes is the apple pie and motherhood of astronomy. It wont do to doubt them.

    But "singularity" you can chuck if you want. I dont care what is inside the event horizon----as long as the thing acts just like a black hole should act on the outside, it can be whatever it wants on the inside

    Maybe inside it is constructed according to a spinfoam quantum zongis theory of an as-yet-unimagined jello-like consistency. I mean it. Why not? Eventually a theory of quantum general relativity will get built and the hope has been (since at least the Sixties) that this would get rid of the "singularities"
    That is a QGR theory will, it has long been suspected, FIX the places where the older Unquantum General Relativity breaks down.
     
  8. Aug 28, 2003 #7

    wolram

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    LOL, marcus you have the gift of the gab your eloquent
    put downs are unmatched, maybe one day i will find
    a theory that confounds you and mainstream science
    but i dout it.
    best wishes
     
  9. Aug 29, 2003 #8
    if there is a giant BH at the center of our galaxy... do you think that a BH is one of the characteristics of any spiral galaxy? hence its flat like, spiraling rotation around its center?
     
  10. Aug 29, 2003 #9

    marcus

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    I have read something about that somewhere. Labguy or chroot would know. I think some people do conjecture that it is commonplace or normal in some sense to have a BH at the center of a spiral galaxy.

    as if black holes are part of what helps spiral galaxies to form

    but I dont remember where I saw that discussed and I dont know how widely the idea is accepted. Maybe Phobos does and will reply here
     
  11. Aug 29, 2003 #10

    Phobos

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    Not irrefutable, but it's the best explanation at the moment.

    Good link on this question...
    http://itss.raytheon.com/cafe/qadir/q78.html
    which says "The answer is that they are the least exotic explanation we can offer for some of the energetic things we are seeing in the universe. "
     
  12. Aug 29, 2003 #11

    Phobos

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  13. Aug 29, 2003 #12

    wolram

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    thankyou for the links PHOBOS
    Messier 106 36M solar masses incredible
    just think of the awe inspiring discoveries yet to come
    i can only say well done hubble
    :smile:
     
  14. Aug 29, 2003 #13

    Labguy

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    Actually, black holes are thought to be at the centers of any type galaxy, especially the giant ellipticals. The BH at the core of M87 is guaged at over one billion solar masses.

    See:
    http://www.mpa-garching.mpg.de/HIGHLIGHT/2002/highlight0207_e.html
     
  15. Aug 29, 2003 #14

    marcus

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    Ahah! so a BH with a radius of two billion miles or more. Roughly the size of the solar system, but spherical. A biggie.

    When do you actually get to move out to dark-skyed Arizona?

    Nice link---with more than usually precise measurements. I've gotten the notion from somewhere that a BH helps a spiral form around it and then those giant ellipticals are formed by the collision and merger of two or more spirals
    so that one actually expects an elliptical to have, or at least have had earlier, more than one large BH in it.
    Cant say where I read this. Have you seen that discussed?
     
  16. Aug 29, 2003 #15

    Phobos

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    If I think of a good link, I'll post it here. But yes, there is a growing body of evidence that every large galaxy has a massive black hole in its center.

    There is also an ongoing debate as to whether those black holes were the cause of, or were caused by, those galaxies. (i.e., did black holes from the infant universe pull in matter to form the galaxies or did galaxies form first and then the supermassive black holes formed in the center of each due to the high concentration of matter in the middle of each galaxy?)
     
  17. Aug 30, 2003 #16
    but there are also black holes not at the center of galaxies correct? I wonder what effect these have on the rotation of galaxies themselves when they contain many black holes not in the center
     
  18. Aug 31, 2003 #17
    Would I miss something but when an agglomeration of energy, an enormous energy droplet, mostly contained inside a definite volume, collapse by its own accretion, its energy density tend to increase to a limit, expressed by Schwarzschild, and, consequently, some UNcontainable energy inside the definite volume, like EM energy, shall propagate out of the "volume" to, progressively, stay within that limit?
    Could I express that limit as space property in term of "kg/m"?
     
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