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    Default Re: Is a black hole made of matter ?



    Quote Originally Posted by astroval View Post
    Or event horizon is just abstraction (not a "thing") it is a wall of fire. It can not be both.
    Hi Astroval (and All),

    The firewall is inside the horizon and is not a part of the horizon, if I understand correctly.

    The reason I put the word "thing" in quotes was an attempt to clarify a misconception that I feel some people have about the horizon. Namely that they think it is a physical object or a material surface. It is NOT. It is an area of spacetime inwhich certain conditions are met, escape velocity greater than or equal to SOL.

    Linguistically, the term "event horizon" is a noun. In that sense it is a thing. But it is an abstract thing, like an idea is a thing yet it has no material existence, it is an abstraction.

    Hope this helps clarify my position.
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    Default Re: Is a black hole made of matter ?

    Quote Originally Posted by Seeker725 View Post
    Hi Astroval (and All),

    The firewall is inside the horizon and is not a part of the horizon, if I understand correctly.

    The reason I put the word "thing" in quotes was an attempt to clarify a misconception that I feel some people have about the horizon. Namely that they think it is a physical object or a material surface. It is NOT. It is an area of spacetime inwhich certain conditions are met, escape velocity greater than or equal to SOL.

    Linguistically, the term "event horizon" is a noun. In that sense it is a thing. But it is an abstract thing, like an idea is a thing yet it has no material existence, it is an abstraction.

    Hope this helps clarify my position.
    My understanding of firewall paradox.

    Firewall, if it exist, located inside horizon. For preventing loss of information, when one of entangled particle cross the event horizon it should disentangle from other one. Mystery appears because total energy of entangled and unentangled particles is different. During disentangle process extra energy emitted which is creating firewall immediately after event horizon. So falling observer detecting firewall will be able to detect the event horizon too. But this contradict to the equivalence principle of GR. I tried explain my understanding of it here.

    To prevent firewall, area where we cannot use GR (singularity) should go to more close to the event horizon, in this case crossing particle after disentangled with outside particle should entangled with particle inside of black hole. In such situation energy for disentangle and entangle completely compensate each other - no firewall, no problem.

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    Default Re: Is a black hole made of matter ?

    I'm getting a lot of interesting and fascinating info here

    However I'm still struggling trying to put my ducks in a row. For ex.:

    Yes, "matter-less" black holes could have existed - theoretically. They could only have been created within the first second after the Big Bang.
    I have now re-watched that documentary over and over and it really doesn't sound like they are talking about a type of BHs that "could have existed theoretically" and that were created within the first second after the Big Bang. It really sounds like they - including Kip Thorne - are talking about the "usual" type of BHs, created in supernovae and mergers and whose existance is reasonably well established.

    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.
    The idea of a size smaller than an atom is actually easier for me to process than the idea of a something-sized sphere with the singularity buried in its center (BTW I'm also still not clear whether the stuff that falls into the BH is thought to stick to the BH's matter part, or to cut through it to reach the singularity and disappear). But anyway NASA's take about the size of the matter part of a BH is different; from that same page:

    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 - think of a star ten times more massive than the Sun squeezed into a sphere approximately the diameter of New York City.
    If it's the size of NYC I'm even more curious as to how the infalling matter reaches the singularity - if it does.

    Should we perhaps conclude that in the scientific community there is no reasonably common consensus on whether non-primordial BHs have a part made of matter and on how big this part is ?
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    Default Re: Is a black hole made of matter ?

    Quote Originally Posted by SantiBailors View Post
    I'm getting a lot of interesting and fascinating info here

    However I'm still struggling trying to put my ducks in a row. For ex.:

    I have now re-watched that documentary over and over and it really doesn't sound like they are talking about a type of BHs that "could have existed theoretically" and that were created within the first second after the Big Bang. It really sounds like they - including Kip Thorne - are talking about the "usual" type of BHs, created in supernovae and mergers and whose existance is reasonably well established.
    One has to be careful about documentaries. Editing by non scientists may distort the understanding. The scientists may acquiesce to that sort of thing once the product is "good enough".

    I think that Kip Thorne very likely understands the difference between a "vacuum solution" black hole (the mass energy content arises purely from space-time curvature) and a "collapsing matter" black hole. The "usual run of the mill" black holes are of the latter variety.

    The idea of a size smaller than an atom is actually easier for me to process than the idea of a something-sized sphere with the singularity buried in its center (BTW I'm also still not clear whether the stuff that falls into the BH is thought to stick to the BH's matter part, or to cut through it to reach the singularity and disappear). But anyway NASA's take about the size of the matter part of a BH is different; from that same page:



    If it's the size of NYC I'm even more curious as to how the infalling matter reaches the singularity - if it does.
    Who says that matter infalling matter reaches the singularity? A distant observer sees infalling matter as taking an infinite time just to reach the event horizon. A falling observer / falling matter does not "penetrate" the matter composing the black hole. All the matter (and observers) composing the black hole see themselves as crossing the event horizon in a finite time and inexorably falling to the central singularity in a finite time. Whether you see things reaching the central singularity depends on your POV.

    Should we perhaps conclude that in the scientific community there is no reasonably common consensus on whether non-primordial BHs have a part made of matter and on how big this part is ?
    No. One should conclude that the documentary and the NASA website have each told partial truths about the situation and have created the appearance of contradiction where there is none. My understanding of the consensus is based on:

    Gravitation (book) - Wikipedia, the free encyclopedia

    While it is about 40 years old the consensus has not been significantly disturbed in that time. My confidence that Thorne's views are not well served by the documentary you've seen is based on that book (co authored by Thorne) and talks by Thorne that I attended. The NASA website insistence that all black holes must be made of matter is contradicted by the fact that the black hole metrics are derived from the vacuum (no matter) solutions of GR's field equations. Odds are most black holes have matter content, but primordial matter less black holes have not been ruled out.
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    Default Re: Is a black hole made of matter ?

    Quote Originally Posted by SantiBailors View Post
    I'm getting a lot of interesting and fascinating info here

    However I'm still struggling trying to put my ducks in a row. For ex.:



    I have now re-watched that documentary over and over and it really doesn't sound like they are talking about a type of BHs that "could have existed theoretically" and that were created within the first second after the Big Bang. It really sounds like they - including Kip Thorne - are talking about the "usual" type of BHs, created in supernovae and mergers and whose existance is reasonably well established.



    The idea of a size smaller than an atom is actually easier for me to process than the idea of a something-sized sphere with the singularity buried in its center (BTW I'm also still not clear whether the stuff that falls into the BH is thought to stick to the BH's matter part, or to cut through it to reach the singularity and disappear). But anyway NASA's take about the size of the matter part of a BH is different; from that same page:



    If it's the size of NYC I'm even more curious as to how the infalling matter reaches the singularity - if it does.

    Should we perhaps conclude that in the scientific community there is no reasonably common consensus on whether non-primordial BHs have a part made of matter and on how big this part is ?
    I agree, the NASA video was referring to black holes comprised of matter, not the matter-less primordial black holes which are only theoretically possible.

    The event horizon is merely an effect created by the mass of the black hole. The bigger the mass, the larger the event horizon. The event horizon is not a physical object, but merely a border (of sorts) that if crossed there is no escape, not even for light. Matter that crosses this event horizon border gets added to the mass of the black hole, which in return increases the size of the event horizon.

    All black holes, that are not primordial, are made of matter. They can only form when temperatures exceed 100 billion degrees Kelvin and there is sufficient pressure. After the first second of the Big Bang the temperature of the universe was not hot enough to produce black holes. However, Population I stars (the very first hydrogen/helium stars) were large enough, and hot enough when they collapsed, to produce black holes. With Population II and III stars (the only ones left in our universe) it requires a star at least 10 M☉, or a stellar core of at least 3 M☉, to become a black hole.

    I think it is a safe assumption to say that black holes are made of matter, with a little footnote exempting the theoretical primordial black holes.
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    Default Re: Is a black hole made of matter ?

    Documentaries try to be entertaining and informative. They are seldom a source for learning. My wife in an anthropologist and even though I think National Geographic makes some of the best documentaries in that field, you should hear the quips from the PhD's.

    Learning can be fun, but it is often tedious. A wise student chooses the source of his/her education.

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    Default Re: Is a black hole made of matter ?

    Although I'm not a student but just an amateur, I agree that a wise student chooses the source of his/her education, and that's what I did. I don't think I should consider unwise choosing Kip Thorne's words and NASA website as sources.

    I agree that documentaries for the general public cannot be relied on much. But this doesn't apply to the part where a top scientist speaks, unless doubts that he was misquoted can be cast.
    In regard to the specific question of whether he was talking about primordial BHs or BHs created from matter, his sentences cannot leave doubts.

    I see no way that anyone who listens to those words can suspect that they were taken out of context or twisted in any way that made it look like he was talking about non-primordial BHs while he was actually talking about primordial BHs.
    Such a claim wouldn't stand after listening to those words; he was clearly talking about non-primordial BHs. The level of reliability of the rest of the documentary is irrelevant to this.

    This is what the says:

    The common idea that a BH is just made of very compacted matter is wrong, it's just simply wrong. They may have been created from very compacted metter, but that matter is gone, it's been completely destroyed, it no longer exists.
    So I can't have any doubts that he was talking about BHs created from matter; I wouldn't know on what to base such doubts.

    Those words - and the words of Paul Davies (Arizona State University) speaking just before Thorne, and the words of other scientists talking about the singularity in other documentaries - are also the reason why it was my understanding that matter falling into a BH is thought to reach the singularity and disappear from our universe. However I might easily have misunderstood this and have it wrong. Thanks for pointing this out.

    Back to whether non-primordial BHs are made of matter, when I try to collect the few facts that I consider certain and I process them logically (through my own logic of course) this is the scenario that comes out:

    - Paul Davies and Kip Thorne were talking about the same type of BHs as NASA was: non-primordial BHs.

    - Paul Davies and Kip Thorne said that those BHs are not made of any matter after their creation.

    - NASA on the contrary says that those BHs are made of a lot of matter, compressed into a sphere ~ the size of NY.

    - Others say that they are made of a lot of matter but compressed into a sphere smaller than an atom.

    - Hence, there is no common consensus on this specific point in the scientific community.

    - Since Thorne said that non-primordial BHs are not made of any matter, that's what I'm going with, at least for now.
    NASA, besides its many amazing achievements, also did things like letting a manned rocket blow up at launch for not wanting to listen to some of their own engineers so I don't see why they can't be cutting corners when writing an educational webpage.

    - I hate this scenario so even though logic and intellectual honesty oblige me to stick to it, I hope I will soon find reasons to change my mind, although currently I don't see how that could happen.
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    Default Re: Is a black hole made of matter ?

    If you read Kip Thorne's (coauthored) own book it is clear that a distant observer never sees infalling matter cross the event horizon in a finite amount of time. So the question of a black hole crushing matter out of existence seems to be more metaphysical than physical. Only an observer falling with the matter sees himself reaching the singularity and destruction.

    - Paul Davies and Kip Thorne were talking about the same type of BHs as NASA was: non-primordial BHs.

    - Paul Davies and Kip Thorne said that those BHs are not made of any matter after their creation.
    It is clear to me, since that there are black holes that are not made of matter (these are solutions of the Einstein field equations I worked through as homework in graduate school) and those that are made by a concentration of matter (as in supernovae). There may be differences in accounting for the formation details among competing detailed scenarios.

    - NASA on the contrary says that those BHs are made of a lot of matter, compressed into a sphere ~ the size of NY.

    - Others say that they are made of a lot of matter but compressed into a sphere smaller than an atom.
    The size of a black hole depends on its mass. The radius is given by R = 2GM / c^2 where G is the gravitational constant, M is the mass and c is the speed of light. A black hole smaller than an atom might be primordial but it can't arise from a supernova. A black hole the size of NY is most likely due to a supernova, less likely a primordial one. So on the size issue you are definitely making a mountain out of a molehill, a contradiction where there is none.

    - Hence, there is no common consensus on this specific point in the scientific community.
    A falsely exaggerated conclusion. The small disagreements due to modeling scenarios are of little significance.

    - Since Thorne said that non-primordial BHs are not made of any matter, that's what I'm going with, at least for now.
    If actually Thorne said that, he made an error according to his own book. The statement would only be true for an infalling observer. It is not true for a distant observer.

    NASA, besides its many amazing achievements, also did things like letting a manned rocket blow up at launch for not wanting to listen to some of their own engineers so I don't see why they can't be cutting corners when writing an educational webpage.
    This is an completely invalid form of argument ad hominem of the sort typically used by "trolls" on internet boards.

    Ad hominem - Wikipedia, the free encyclopedia
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    Default Re: Is a black hole made of matter ?

    Quote Originally Posted by SantiBailors View Post
    Although I'm not a student but just an amateur, I agree that a wise student chooses the source of his/her education, and that's what I did. I don't think I should consider unwise choosing Kip Thorne's words and NASA website as sources.

    I agree that documentaries for the general public cannot be relied on much. But this doesn't apply to the part where a top scientist speaks, unless doubts that he was misquoted can be cast.
    I'm sorry if I offended you with the adage. In fact IMO you became a wise student when you posted your question and continue to discuss it.

    In my experience people like Thorne and Davies need at least an hour to establish context for statements like the ones you quote. If edited, I must allow for the possibility that the editor didn't provide the intended context.

    Quotes from NASA, on the other hand, are always suspicious. Those are often meant to get public support for funding.

    Thanks for the thread and the discussion.
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    Default Re: Is a black hole made of matter ?

    Quote Originally Posted by not_Fritz_Argelander View Post
    The size of a black hole depends on its mass. The radius is given by R = 2GM / c^2 where G is the gravitational constant, M is the mass and c is the speed of light. A black hole smaller than an atom might be primordial but it can't arise from a supernova. A black hole the size of NY is most likely due to a supernova, less likely a primordial one. So on the size issue you are definitely making a mountain out of a molehill, a contradiction where there is none.
    Is 2GM / c2 the radius of the Event Horizon or the radius of the singularity?

    I ran the equation using Sol as an example, and came up with 2,954 meters

    G = 6.6738 × 10-11
    M = 1.9891 × 1030 kg
    c = 299,792,458 m/s
    Last edited by Glitch; 06-15-2013 at 06:37 PM.

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