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    Question Is a black hole made of matter ?



    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:

    Don't let the name fool you: a black hole is anything but empty space. Rather, it is a great amount of matter packed into a very small area
    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.
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    Default Re: Is a black hole made of matter ?

    Quote Originally Posted by SantiBailors View Post
    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.
    Actually both your alternatives, made of nothing or made of very dense matter, are correct. Both of your sources are guilty of oversimplifying and telling only part of the story.

    General Relativity (GR) is a nonlinear theory, unlike electromagnetism (EM) which is linear. In linear theories the fields are caused by sources which are distinct from the fields themselves. In nonlinear theories like GR the fields (curvature of space time) can also be caused by the fields. The standard "black hole solutions" of GR were all first obtained as vacuum or no source solutions to GR.

    In that sense Kip Thorne is right, but it is only half the story. Matterless black holes can only be created in the Big Bang.

    If you compress a lot of matter into a little space and compress it hard enough (in the right kind of supernova, or merger of the right kind of stars) you can also get a black hole. In that sense the NASA website is right but it only tells half the story.

    Kudos to you for spotting the contradiction!
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    Default Re: Is a black hole made of matter ?

    We have sufficient observations of gravitational lensing, motion of the stars in galaxies, X-rays, etc. to accept GR as the best mathematical model of a bh that we have. GR predicts an event horizon as a boundary, a point of no return.

    But GR allows for several solutions and doesn't tell us which one is correct for inside the event horizon. Since GR fits the observables, we like to stay with it outside the event horizon. But inside is unknown. People like Kip Thorne are looking at solutions for what goes on inside that might affect the observations on the outside.

    Since GR tells us that energy and mass are equated, it isn't clear to me that we need to distinguish them in some cases such as within the event horizon. But GR also predicts a troublesome singularity at the center of a bh. No one can answer your question yet.

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    Default Re: Is a black hole made of matter ?

    Quote Originally Posted by not_Fritz_Argelander View Post
    Actually both your alternatives, made of nothing or made of very dense matter, are correct. Both of your sources are guilty of oversimplifying and telling only part of the story.

    General Relativity (GR) is a nonlinear theory, unlike electromagnetism (EM) which is linear. In linear theories the fields are caused by sources which are distinct from the fields themselves. In nonlinear theories like GR the fields (curvature of space time) can also be caused by the fields. The standard "black hole solutions" of GR were all first obtained as vacuum or no source solutions to GR.

    In that sense Kip Thorne is right, but it is only half the story. Matterless black holes can only be created in the Big Bang.

    If you compress a lot of matter into a little space and compress it hard enough (in the right kind of supernova, or merger of the right kind of stars) you can also get a black hole. In that sense the NASA website is right but it only tells half the story.

    Kudos to you for spotting the contradiction!
    I was just about to say that anything with mass must contain matter, then I read your post...

    It had not occurred to me that primordial black holes were indeed a "matter-less" object because they could only have occurred before the first second after the Big Bang (prior to the Lepton Epoch) when temperatures and pressures were still sufficient to create black holes.

    Everything I have read about primordial black holes suggest they are very small in mass in comparison to their stellar cousins. They theorize that primordial black holes no longer exist, having evaporated due to Hawking Radiation. My question is why would all primordial black holes have to be low mass? Since they could have formed long (relatively speaking) after the Inflation of the universe when temperatures were still above a 100 billion degrees Kelvin, could it have been possible for stellar-size, or larger, mass primordial black holes to have formed? And if so, would they not still be around today?

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    Default Re: Is a black hole made of matter ?

    Quote Originally Posted by Glitch View Post
    It had not occurred to me that primordial black holes were indeed a "matter-less" object because they could only have occurred before the first second after the Big Bang (prior to the Lepton Epoch) when temperatures and pressures were still sufficient to create black holes.
    It is at least possible that matterless black holes could be made in the Big Bang. We don't have a theory that works that early yet.

    Everything I have read about primordial black holes suggest they are very small in mass in comparison to their stellar cousins. They theorize that primordial black holes no longer exist, having evaporated due to Hawking Radiation. My question is why would all primordial black holes have to be low mass? Since they could have formed long (relatively speaking) after the Inflation of the universe when temperatures were still above a 100 billion degrees Kelvin, could it have been possible for stellar-size, or larger, mass primordial black holes to have formed? And if so, would they not still be around today?
    I don't think it is necessary that all primordial black holes be tiny. However one expects a distribution of masses ranging from Planck mass on up. The tiny one's are the easiest to detect though.

    Speculation.... An initial distribution of vacuum black holes is formed in the Big Bang ranging from Planck masses to larger. As time goes on some of them can merge to form larger black holes. In addition they all start accreting some matter so that their "vacuum" isn't so pure any longer. So the scenario can get complicated quickly. I see no reason to rule out stellar mass black holes that could survive to the present day. It looks like dark matter and black holes formed at an early time are necessary to seed galaxy formation.

    Any early black holes that became seeds for galaxies would likely accumulate enough matter so that they are no longer pure vacuum solutions.
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    Thumbs up Re: Is a black hole made of matter ?

    Thanks for the clarifications. So if I understood correctly matterless BHs exist, they were created in the Big Bang and they are the ones the two scientists are talking about, while NASA was talking about BHs made of matter, which exist as well and are created in supernovas and mergers.

    It's totally disappointing that neither of those so authoritative sources bothered to specify that they were only talking about one type of BH and that for the other type the opposite is true. Especially if one of the two types is thought to no longer exist. As an outsider science enthusiast I can assure that many would-be science enthusiasts get pushed away by this type of things while many science-bashers just live and prosper by these things.
    At least in the case of that documentary I will go with the idea that the scientists had specified that difference and the editors left it out.

    So I realized that I will have to read about primordial BHs.
    Thinking of BHs with a body made of matter, I imagine that the singularity is in the very center of the body. If so, does the matter that falls into a BH cut through the matter of the BH body and reaches the singularity and so disappears from our universe, or does it never reach the singularity and just sticks to the BH body ?
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    Default Re: Is a black hole made of matter ?

    Quote Originally Posted by SantiBailors View Post
    Thanks for the clarifications. So if I understood correctly matterless BHs exist, they were created in the Big Bang and they are the ones the two scientists are talking about, while NASA was talking about BHs made of matter, which exist as well and are created in supernovas and mergers.

    It's totally disappointing that neither of those so authoritative sources bothered to specify that they were only talking about one type of BH and that for the other type the opposite is true. Especially if one of the two types is thought to no longer exist. As an outsider science enthusiast I can assure that many would-be science enthusiasts get pushed away by this type of things while many science-bashers just live and prosper by these things.
    At least in the case of that documentary I will go with the idea that the scientists had specified that difference and the editors left it out.

    So I realized that I will have to read about primordial BHs.
    Thinking of BHs with a body made of matter, I imagine that the singularity is in the very center of the body. If so, does the matter that falls into a BH cut through the matter of the BH body and reaches the singularity and so disappears from our universe, or does it never reach the singularity and just sticks to the BH body ?
    Yes, "matter-less" black holes could have existed - theoretically. They could only have been created within the first second after the Big Bang. Matter, on the other hand, did not come into existence until around 70,000 years after the Big Bang. Personally, I place the existence of matter during Nucleosynthesis which occurred during the Photon Epoch, between 3 minutes and 20 minutes after the Big Bang. During that 17 minute window every element in the universe was created.

    I think NASA was simply referring to the stellar-type black hole, which are by far more common. "Matter-less" black holes, or primordial black holes, which could only have been created within the first second of the Big Bang, before baryonic matter existed, is getting pretty esoteric. When I first read about them it took a while to wrap my head around the concept.

    In regard to black holes that contain matter, yes, the singularity is the very center of the black hole. Think neutron star (about 10 miles in diameter), now add more mass, and then crush it down to the size smaller than an atom. Depending upon the mass of the black hole, an event horizon forms. Anything, including light, that passes this event horizon cannot escape and is added to the mass of the black hole.
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    Default Re: Is a black hole made of matter ?

    During the Hadron Epoch, less than a millionth of a second after the Big Bang, the temperature of the universe was still 10,000,000,000,000° K (10^13). Which is hot enough to form a black hole, given sufficient pressure. By the time the first second had elapsed the universe had cooled to 10,000,000,000° K (10^10), which is no longer hot enough to form black holes. This is why it requires a massive star to create black holes. Nothing else since the Big Bang can reach those kind of temperatures and pressures other than a supernovae.
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    Default Re: Is a black hole made of matter ?

    The event horizon is not a "thing". It is a location in space a certain radial distance from the center of the BH, where escape would require a speed that is equal to or faster than light. It is not a physical membrane in the classical sense but can be treated as such in abstract. As material falls in past that radius, whether it is matter or energy, all paths lead to the center of the BH, the singularity. The more massive the BH is, the farther the horizon is from the center. As material falls in the BH gets more massive and the horizon's radius gets larger.

    The space between the singularity and the horizon is relatively empty. It is occupied by the material that has just crossed the horizon and has not yet reached the singularity. Nothing stays in this zone for very long. We don't know exactly what happens as material is incorporated into the singularity. Relativity works very well until you get close to the singularity and Quantum Mechanics, so far, does not provide an answer either, yet.

    There are other horizons as well, an inner horizon, an apparent horizon and an absolute horizon. If the BH is spinning, and real BH's are pretty much all expected to have some spin no matter how minute the spin rate is, the singularity is expected to have a ring-like shape. The faster the spin rate the more the event horizon is distorted out of perfectly round into an oblate spheroid.

    Mass, spin, and charge, are the only properties of a BH that you can determine about the BH from the outside of the BH. You can't tell if the BH was made of matter or energy or ironing boards or spinning pink unicorns, from outside the BH. Leonard Susskind (and others) believe the information of the BH's formation is stored on the surface of the event horizon, and close examination of the Hawking Radiation as the BH evaporates will reveal its composition history. (This is one abstract way an event horizon can be treated as a physical membrane.)

    The singularity, like the "dark" term in dark energy and dark matter, is a cautionary label. It is like the old map maker's "There be dragons" on an old chart. It warns the thinker that all is not understood about this object. When the properties of singularities are understood they singularities will be renamed to reflect the new understanding. A singularity in a BH is infinitely small, infinitely dense and warps spacetime an infinite amount. Since the material that comprises any BH is finite and any BH formed a finite time in the past, no physical property of a BH can become infinite in finite time. The equations all point to infinities at the singularity and these infinities are unphysical, yet we have no clear way to resolve the infinities. Fortunately the equations hold until you get really close to the singularity, so you can disregard infinite weirdness as long as you remember to isolate your speculations to a safe Planckian(?) distance.

    Recent speculations by the really big brains in the field propose a "firewall" of hot energetic particles that will meet and incinerate any infalling observer well before they reach the singularity. The mechanism for the generation of the firewall, if i understand it correctly, and I probably don't have the concepts firmly in grasp is thus...When a BH forms it immediately begins to Hawking Radiate. The radiation that escapes is entangled with the radiation that fell in, and as the BH ages the amount of entangled material builds up over time. The firewall moves out from the center and moves closer and closer, but never quite reaches, the event horizon. A young BH's firewall is close to the singularity and an old BH's firewall is near the event horizon.

    Cool stuff !!!!
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    Default Re: Is a black hole made of matter ?

    Quote Originally Posted by Seeker725 View Post
    The event horizon is not a "thing". It is a location in space a certain radial distance from the center of the BH, where escape would require a speed that is equal to or faster than light. It is not a physical membrane in the classical sense but can be treated as such in abstract.

    Recent speculations by the really big brains in the field propose a "firewall"
    Or event horizon is just abstraction (not a "thing") it is a wall of fire. It can not be both.
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