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Thread: Is a black hole made of matter ?

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    Default Re: Is a black hole made of matter ?



    I think that you may intend the numbers in your question as figurative. The falling observer sees the distant observer age more rapidly. How fast depends on details such as the mass of the black hole. the falling observer see himself as colliding with the central singularity in a finite amount of time. Whether he sees "millions" of years aging in a few minutes of falling depends on details.
    Thanks Fritz! As if imagining the distant observer age rapidly wasn't a problem already, now I'm struggling to imagine what a singularity would look like.

    There is other legend, which said A crossing horizon will be able see "video" from this moment up to the end of the Universe. This legend is not true.
    Yes, that sounds more like the legend I was referring to.

    You mentioned the event horizon and how it would mess up the order of the photons, etc. Do you think the same would apply to naked singularities?

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    Default Re: Is a black hole made of matter ?

    Quote Originally Posted by Celestica View Post
    You mentioned the event horizon and how it would mess up the order of the photons, etc. Do you think the same would apply to naked singularities?
    It's not so much that the event horizon would "mess up the order" of photons. They would arrive in proper sequence to an interior observer. But remember the falling interior observer has only a limited time before hitting the singularity (or being tidally destroyed). So there just may not be enough time for the falling observer to see the whole history of the universe.

    Your naked singularity question gives me a headache.
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    Default Re: Is a black hole made of matter ?

    Quote Originally Posted by SantiBailors View Post
    This is my first question on these forums... Please keep in mind that I'm just an amateur with no relevant education at all and my knowledge is extremely limited.

    Whenever I tried to "visualize" a black hole I always wondered whether I should think of a concrete "object", meaning something somehow made of matter, or instead I should think of an empty region of space.

    In this documentary (more or less between 08:00 and 09:00) two scientists who in my understanding are rightly well respected worldwide (one is Kip Thorne) say that black holes are not made of matter at all.

    However NASA website in my understanding is saying exactly the opposite:



    I hope someone can help me figure out whether I'm misunderstanding the wording of one of the two sources (or both) or I'm missing something that those sources are taking for granted.
    Welcome to the forum.

    I'm revisiting your question and instead of saying whether a BH is made of matter or not, rather, explaining what a BH is made of.

    The Event Horizon (EH) is the radial spherical distance from the center of mass of the BH where an object would need to be traveling at the speed of light to escape it's gravitational influence. It is not a solid surface. It is not a gaseous or liquid surface either. The EH is made of spacetime. Its made of "nothing". Spacetime is not nothing. Spacetime has properties. Nothing doesn't have properties. Some of the properties of spacetime are...length, width, height; the speed of light is fixed by the permittivity and permeability of spacetime; virtual particle pairs pop into and out of existence on the stage of spacetime as evidenced by the Casimir Effect. Spacetime can be distorted, lengths widths and heights as well as time are malleable. Gravity distorts spacetime. This is what the EH is made of, immensely distorted spacetime curvature.

    What causes the powerful distortion? Mass. Mass is usually thought of as a property of matter and not usually as a property of energy but energy in confinement does behave as though it has mass. The mass of the BH is all the stuff that has ever fallen into the BH. It is the core of the massive sun that collapsed to form it plus anything else that ever was drawn to it and crossed the EH, including any light that crossed the horizon as well.

    The mass of the BH's contents determines how far out the EH is from the center. The more massive the BH the larger is the distance across the EH. Since mass is a property of matter and energy you cannot tell from the outside what proportions contributed to the hole's formation, or how those proportions may have changed over time.

    There is an additional question that arises when you consider what might happen to matter as it is subjected to the extreme tidal forces of the center of the BH. The tidal forces pull hard on the side of a particle of mass that is closest to the center and less hard on the most distant part of the matter particle. The difference in the strength of the pull may be strong enough and chaotic enough to shred the matter and convert the matter to energy before it hits the center. In that sense it may be more appropriate to say a BH is made of energy not matter, if the matter is destroyed before it is truly incorporated into the center.

    All the mass of the BH is concentrated in the center, the singularity. Not all the energy of a BH is in the center. A BH has angular momentum, spin. The spin causes the center to assume a ring like shape. It also distorts the EH by making it bulge out of perfect roundness perpendicularly to the axis of rotation of the BH.

    A BH can have charge as well, and the charge can be measured from outside the EH. Most BH's if not all, are not expected to have much charge since charge readily attracts the oppositely charged particles which would quickly neutralize any net charge.

    You can't see the center, you can't see the warped spacetime extending from the center to the EH. You can't see the warped spacetime extending from the EH outward either, but you can see the effect that the warped spacetime has on the material that moves through it. And in this way the overall size and shape encompassed by the EH is revealed as a nearly perfect spherical volume.

    So, a BH is made of mass, charge and spin energies. There is a miniscule yet extremely massive dot in the center, and powerfully warped spacetime all the way out to the EH and beyond. Remember the EH is just a region where the SOL escape velocity transition is relevant, the warped spacetime extends beyond the EH with the warpage diminishing as distance from the center increases.

    Warped spacetime.
    Last edited by Seeker725; 06-19-2013 at 12:08 AM.
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  7. #34
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    Default Re: Is a black hole made of matter ?

    Quote Originally Posted by Celestica View Post

    Yes, that sounds more like the legend I was referring to.

    You mentioned the event horizon and how it would mess up the order of the photons, etc. Do you think the same would apply to naked singularities?
    Some strange stuff happens when Alice jumped and crossed event horizon of black hole and after that later Bob decided to do the same. Alice will see that Bob will reach singularity before her. Never understand it.

    As far as naked singularity, only the Big Bang naked singularity can exist in the universe (see cosmic censorship hypothesis). Our universe is result of Big Bang naked singularity - this is looks like what we see now.

    I think it is very difficult to explain what happen inside black hole because our intuition not working for this case. Also some results depends from different kind of black hole - stationary, rotating, charged. It is real Zoo! Some even stationary orbits can be inside event horizon of rotating charged black hole! (Planets Could Orbit Singularities Inside Black Holes)

    There is interesting website of professor at University of Colorado - Andrew Hamilton. He tried to show animated videos of the interiors of black holes:

    Journey into a Schwarzschild black hole

    Journey into and through a Reissner-Nordström black hole

    He has very nice Warning on the web site

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  9. #35
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    Default Re: Is a black hole made of matter ?

    Quote Originally Posted by astroval View Post
    Some strange stuff happens when Alice jumped and crossed event horizon of black hole and after that later Bob decided to do the same. Alice will see that Bob will reach singularity before her. Never understand it.
    I don't think that can be a correct result. Would you care to elaborate? I think that if one is not careful about how one matches interior and exterior metrics and make a mistake it could look like that. But there is a need to be careful about matching metrics at the event horizon. Certainly in the local Lorentz frame of Alice, Bob has no "leapfrogging" ability with both in free fall.

    One old solution (1939) by Oppenheimer and Snyder does a good job on free falling dust ball. (Mass but no pressure.) The external metric is Schwarzchild but the interior metric is FLRW.

    Oppenheimer-Snyder Collapse - GRwiki

    http://arxiv.org/pdf/1109.0546v1.pdf

    So black holes made of stuff are active topics of research. The interest is to see whether the singularity of the vacuum solution can be avoided. Of course a lot depends on the equation of state of matter and at the relevant densities we have no data, only guesses.
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    Default Re: Is a black hole made of matter ?

    Quote Originally Posted by not_Fritz_Argelander View Post
    I don't think that can be a correct result. Would you care to elaborate? I think that if one is not careful about how one matches interior and exterior metrics and make a mistake it could look like that. But there is a need to be careful about matching metrics at the event horizon. Certainly in the local Lorentz frame of Alice, Bob has no "leapfrogging" ability with both in free fall.
    I was wrong, solar eclipse during 2 minutes It was just misinterpretation of different world lines in the Kruskal diagram. Situation inside black hole don’t have this strange stuff. Thanks for correction.


    Just founded one more Hamilton video on YouTube



    As I understand he used static picture outside the black hole, pretty much assuming that Alice for limited time see only limited number of photons from limited area. Next time instead of buying new telescope just need to buy small supercomputer which able to draw non-static picture for falling frame of reference

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    Default Re: Is a black hole made of matter ?

    Quote Originally Posted by astroval View Post
    I was wrong, solar eclipse during 2 minutes It was just misinterpretation of different world lines in the Kruskal diagram. Situation inside black hole don’t have this strange stuff. Thanks for correction.
    No worries.

    Just founded one more Hamilton video on YouTube

    As I understand he used static picture outside the black hole, pretty much assuming that Alice for limited time see only limited number of photons from limited area. Next time instead of buying new telescope just need to buy small supercomputer which able to draw non-static picture for falling frame of reference
    It's a good video. I think it represents the case when there is very little matter "composing" the black hole very well. It is a good tour of a vacuum black hole.

    In truth it would be very hard to portray the interior of a black hole made of matter. The 1939 Oppenheimer-Snyder solution for a pressureless dust would be very different (no singularity). But pressureless dust is not a realistic equation of state. It might be interesting to see if there is a video for an ultrarelativistic equation of state: pressure = density * c^2. Anyone want to program that up on their home supercomputer?

    Hamilton has a complete textbook on General Relativity available as a pdf download here:
    http://jila.colorado.edu/~ajsh/phys5770_13/grbook.pdf

    It looks thorough and complete with, I think two reservations:
    1) a prejudice or taste preference for discussing vacuum black holes rather than considering black holes with stuff inside
    2) he uses the "illusion" language in discussing reconciling the different observations of a falling and a distant observer, which I think is a mistake as I've noted elsewhere. (In GR there is no need to harmonize those POVs. It's a human need. )

    Aside from those mild caveats its a fine treatment and recommendable.
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    Default Re: Is a black hole made of matter ?

    Hello All,

    not_Fritz,
    In the fervor of our last few conversations I forgot to thank you for the links you posted and referred me to. Thank You. You have the patience of Job pal. GR was built to account for the gravitational issues, I accept that. I thought I might have found a chink in the GR armor but realize the folly now. Every reference frame is its own reality. There are a nearly if not truly infinite number of valid frames. I don't like it but nature doesn't care what I like (to coin another frequent poster's phrasing). I would much prefer that nature singles out a concrete individual reality but all indications are that that would be the true "Grand Illusion". Even QM in many ways leads to this conclusion.

    Astroval, thank you for the multiple interesting BH videos, I enjoyed those also.

    I have a question for not_Fritz regarding the structure of black holes...

    What do you think the structure hierachy is for a real, moderately spinning, minimally charged, BH ?
    I think many posters would be interested to hear your thoughts. If there is a link to a particular model that closely correspond to your ideas that would be fine and appreciated as well I'm sure. Thanks in advance and thanks again for every thing else.

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    Default Re: Is a black hole made of matter ?

    Quote Originally Posted by Seeker725 View Post
    Every reference frame is its own reality.... I would much prefer that nature singles out a concrete individual reality but all indications are that that would be the true "Grand Illusion". Even QM in many ways leads to this conclusion.
    I've had to struggle with this as well in refining my understanding. So I tend to be a nag about it. Thanks for your patience as well.

    What do you think the structure hierachy is for a real, moderately spinning, minimally charged, BH ?
    I think many posters would be interested to hear your thoughts. If there is a link to a particular model that closely correspond to your ideas that would be fine and appreciated as well I'm sure. Thanks in advance and thanks again for every thing else.
    Fortunately where I am sitting at the moment I can reach out and touch my copy of MTW which has a nice summary of Kerr-Newman geometry on pp. 878-883.

    The following is for a vacuum solution. There is both an outer and an inner horizon that bound a region called an ergosphere where a particle can escape the outer horizon by splitting in two, dumping a piece into the inner horizon, and the remaining piece escapes the hole at the expense of the rotational energy of the hole. The point singularity is replaced by a ring singularity around the hole center.

    Online there are pictures here:
    River model of a rotating (Kerr-Newman) black hole
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    Default Re: Is a black hole made of matter ?

    Quote Originally Posted by not_Fritz_Argelander View Post
    The point singularity is replaced by a ring singularity around the hole center.
    PS Sorry for the self follow but I forgot to add:

    I expect that with enough matter present, the ring singularity would disappear. I have no calculations to back that up. It is just an intuition that makes an analogy with the presence of matter in a Schwarzschild black hole interior. The Oppenheimer-Snyder (1939) solution shows the singularity disappears and is completely regularized.
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