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Thread: learning black hole theory

  1. #1 learning black hole theory 
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    This thread is for everything and anything related to black hole theory. Tests pertaining to black hole theory whether failed or not. Ideas people had etc and discussion.


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    Sup fiveworlds

    Maybe post a few links to info. Then we can the thread going.


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    By "black hole theory" I assume you mean General Relativity?

    There is a lot of observational evidence. For example, the orbits of stars around Sagittarius A* at the center of our galaxy: Max Planck Institut für extraterrestrische Physik | Science | Infrared Astronomy | Research | Galactic Center
    Or orbital speeds and therefore mass in other galaxies: Evidence for Black Holes
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    I wanted to ask about the theory of pulsars collapsing into black holes is it true that we can only see a pular when the beam of light is pointed directly at the planet and if so why?
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    Quote Originally Posted by fiveworlds View Post
    I wanted to ask about the theory of pulsars collapsing into black holes is it true that we can only see a pular when the beam of light is pointed directly at the planet and if so why?
    As I understand it, a pulsar is the remnants of a supernova and hence very small (a neutron star maybe?) and spinning very fast. This means they have very powerful magnetic fields. Any gas and dust that falls towards them gets accelerated and heated and then ejected along the line of the axis. This forms a tightly focused beam like flashlight. If this points in our direction we see a flash.
    220px-Pulsar_schematic.svg.png
    Pulsar - Wikipedia, the free encyclopedia
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    i was wondering about something hawking surmised that black holes emit thermal radiation the temperature increasing as the black hole decreases in size. If a black hole was a quazar moving fast enough to reduce the speed of photonic particles below the quantum boom barrier then the 'light' particles would not have enough energy to be seen as light
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    Quote Originally Posted by fiveworlds View Post
    i was wondering about something hawking surmised that black holes emit thermal radiation the temperature increasing as the black hole decreases in size.
    This also means that small black holes (small enough to emit significant energy) do not last very long - they radiate away.

    If a black hole was a quazar moving
    My understanding is that quasars are the supermassive black holes at the center of galaxies.

    fast enough to reduce the speed of photonic particles below the quantum boom barrier
    Photons always travel at the speed of light. What is the "quantum boom barrier"?
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    easy to understand so.quantum boom is wrong context here. what i mean is that the quazar causes a reduction in the wavelength of the emitted light below the range of the visible spectrum.what about the kerr black hole?
    Last edited by fiveworlds; February 4th, 2013 at 05:42 PM.
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    [astro-ph/9801252] Black Holes : A General Introduction

    Our understanding of space and time is probed to its depths by black holes. These objects, which appear as a natural consequence of general relativity, provide a powerful analytical tool able to examine macroscopic and microscopic properties of the universe. This introductory article presents in a pictorial way the basic concepts of black hole's theory, as well as a description of the astronomical sites where black holes are suspected to lie, namely binary X-ray sources and galactic nuclei.
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    if im honest i stopped reading this at page sixteen im seeing flaws
    1 particles cannot move faster than the speed of light.
    2 a black hole can never split into two parts
    3 if a black hole is connected to a white hole then where is a white hole?
    Last edited by fiveworlds; February 4th, 2013 at 08:05 PM.
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    Current theory says a black hole is matter that has collapsed into a singularity. I do not believe singularity's exist in nature, it's nothing more than a mathematical representation. No one knows where the matter surface of a black hole is on the other side of the event horizon. It could be just one inch or miles below the EH, and we wouldn't ever know.

    Matter density keeps advancing in stages of quantum degeneracy pressure. First we have white dwarfs where the electron shells of the atoms are greatly compressed close to the nucleus. Next we have neutron stars where the electrons combine with the protons and they become neutrons. After that it has been suggested there might be Quark stars before a BH is formed. I don't know what happens on the other side of an EH and neither does anybody else. But I would suggest that the stages of degeneracy don't quit just because they are on the other side of the EH and we don't yet have ways to probe to deeper levels of the atomic structure of atoms than quarks.
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    now that makes perfect sense to me arkane. I also think it could be possible to have different types of black hole other than a typical quazar. with different compositions etc. is there any other theories?
    Last edited by fiveworlds; February 4th, 2013 at 09:21 PM.
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    Quote Originally Posted by fiveworlds View Post
    now that makes perfect sense to me arkane. I also think it could be possible to have different types of black hole other than a typical quasar. with different compositions etc. is there any other theories?
    It sounds like you are using quasar and black hole as being the same thing? They are not the same thing. A quasar is an active supermassive black hole. Active means it has a great deal of mass falling into it continuously as the mass gets accelerated to near light speed, it heats up and gives off a great deal of energy. Enough so that the whole galaxy shines very bright. During the time when galaxies were forming, a big part of that process had to be very active SMBH's. That's why most of the quasars we can see are very far away in both distance and time. Once galaxies got past that start up phase the BH's were becoming less active to a point where they lose their quasar status. This is very good because life might have trouble developing in a galaxy that was still an active quasar.
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    Quote Originally Posted by fiveworlds View Post
    if im honest i stopped reading this at page sixteen im seeing flaws
    What flaws are you seeing?

    1 particles cannot move faster than the speed of light.
    Correct. Do you disagree with that?

    2 a black hole can never split into two parts
    Correct. Do you disagree with that?

    3 if a black hole is connected to a white hole then where is a white hole?
    As the article says, it is in a:
    “parallel” universe (whatever the physical meaning of such a statement may be)
    There is currently no evidence that white holes physically exist in our universe.
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    Quote Originally Posted by fiveworlds View Post
    what i mean is that the quazar causes a reduction in the wavelength of the emitted light below the range of the visible spectrum.
    Are you talking about the gravitational red shift of light near a black hole? Then yes, any light emitted from something approaching the event horizon will be increasingly red shifted. Out of the visible spectrum to infra-red and beyond. Until no more light is emitted.

    what about the kerr black hole?
    It is probable that pretty much all black holes are Kerr black holes. They will almost certainly be rotating and will have little or no charge.
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    with different compositions etc. is there any other theories?
    At this point in time anything that happens beyond the event horizon is mere speculation and conjecture. There are, however, a few interesting models - check out for example the "Fuzzball" hypothesis :

    Fuzzball (string theory) - Wikipedia, the free encyclopedia
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    why do ppl think, under classical bh theory, that information simply vanishes?

    after the sun turned into a bh it bends space more. if more matter/energy falls in, doesn't it simply continue bending space without the radius increasing?
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    Quote Originally Posted by curious mind View Post
    why do ppl think, under classical bh theory, that information simply vanishes?

    after the sun turned into a bh it bends space more. if more matter/energy falls in, doesn't it simply continue bending space without the radius increasing?
    No, the radius of the event horizon is a function of its total mass. If the mass increases, so does the BH's radius; and since the BH's entropy is in turn a function of the total event horizon area, so does its entropy too. Thus information is not ever lost, it just get's "garbled" and shows up in the form of entropy.
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    after a sun turned into a black hole, its density compared to its mass is much higher than what the sun had, right? so it will bend space more (and probably also spin faster).

    now imagine a table with a hole in it and a table cloth lying on the table. since the blackholes radius is much smaller than what the sun has been, with a high density; it would be = to place a ball on the table cloth over the hole.

    it would bend space more than the sun did.

    and due to this take space with it, or makes it look as if space vanishes into the black hole.

    now if you would throw, let's say, 10 marbles in that hole on the table, the mass in the hole would increase and bend space more; but the radius would still be the same.
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    Quote Originally Posted by curious mind View Post
    after a sun turned into a black hole, its density compared to its mass is much higher than what the sun had, right? so it will bend space more (and probably also spin faster).

    now imagine a table with a hole in it and a table cloth lying on the table. since the blackholes radius is much smaller than what the sun has been, with a high density; it would be = to place a ball on the table cloth over the hole.

    it would bend space more than the sun did.

    and due to this take space with it, or makes it look as if space vanishes into the black hole.

    now if you would throw, let's say, 10 marbles in that hole on the table, the mass in the hole would increase and bend space more; but the radius would still be the same.
    I think you are confusing pop-sci analogies of space-time with the real thing. The radius of the event horizon is a simple function of the BH mass :



    Herein M is the total mass of the BH, and G and c are constants.
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    i haven't start looking it up, but you say the function only accounts for the mass of the black hole. but 2 objects of the same mass but different sizes behave different.
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    Quote Originally Posted by curious mind View Post
    now if you would throw, let's say, 10 marbles in that hole on the table, the mass in the hole would increase and bend space more; but the radius would still be the same.
    The point is that the radius increases with the mass. Add 10% more mass and the radius incerases by 10%. Double the mass, the radius doubles.

    Quote Originally Posted by curious mind View Post
    but 2 objects of the same mass but different sizes behave different.
    I'm not sure what you mean by that. But at a given distance, the gravitational effect depends only on the mass. For example, if evil aliens suddenly replaced the sun with a black hole of the same mass, it would make no difference to the orbits of the planets. (But it would get even colder than it is at the moment.)
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    if that sun had a radius of 500 000 km, and the replaced black hole were only 50 km wide; it would be much denser than the sun was.
    on average the density would be the same, but not at the black hole itself.

    so we observed the increasing of a black holes radius?
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    Quote Originally Posted by curious mind View Post
    if that sun had a radius of 500 000 km, and the replaced black hole were only 50 km wide; it would be much denser than the sun was.
    on average the density would be the same, but not at the black hole itself.
    By "on average the density would be the same", you mean the density within the original volume of the sun? That would, clearly, be the same (same mass in the same volume). But the average density within the black hole's event horizon would be much, much higher (same mass in a smaller volume).

    Although, I'm not sure that it makes much sense to talk of the volume of a black hole, strictly speaking...
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    Quote Originally Posted by Strange View Post
    Quote Originally Posted by curious mind View Post
    if that sun had a radius of 500 000 km, and the replaced black hole were only 50 km wide; it would be much denser than the sun was.
    on average the density would be the same, but not at the black hole itself.
    By "on average the density would be the same", you mean the density within the original volume of the sun? That would, clearly, be the same (same mass in the same volume). But the average density within the black hole's event horizon would be much, much higher (same mass in a smaller volume).

    Although, I'm not sure that it makes much sense to talk of the volume of a black hole, strictly speaking...
    so the same mass distributed/spread over less space/surface would bend the space/surface more by the factor of change, or not?

    and did we observe the radius of a black hole increasing?
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    Quote Originally Posted by curious mind View Post
    so the same mass distributed/spread over less space/surface would bend the space/surface more by the factor of change, or not?
    I'm not quite sure what you are asking. But the key thing about a black hole is that the mass is squeezed into a small enough volume (within the Schwarzschild Radius).

    and did we observe the radius of a black hole increasing?
    No, because we have not yet directly observed a black hole. (And I'm not sure that you would be able to see the radius increase unless you happened to catch it swallowing an entire star, or something.)
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    so our sun would become a black hole when it's radius were 3km. having the same mass squeezed down to that would bend space more at that point, wouldn't it?
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    Quote Originally Posted by curious mind View Post
    so our sun would become a black hole when it's radius were 3km. having the same mass squeezed down to that would bend space more at that point, wouldn't it?
    Black holes that small don't exist, so why use it as an example? Our sun might be able to produce a white dwarf at the most. Needs much more mass to produce a black hole.
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    it's only an example to show how dense an object becomes for it to collapse under the force of its own gravity.
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    Quote Originally Posted by curious mind View Post
    so our sun would become a black hole when it's radius were 3km. having the same mass squeezed down to that would bend space more at that point, wouldn't it?
    A black hole the mass of our sun would have a radius of about 30km (I think - no, out by a factor of 10).

    Yes, the curvature of space-time would be greater at that point than at 30km from the center of the sun (because there is a lot more mass inside that radius in the black hole case.

    The curvature of space-time at the radius of the sun (and beyond) would be the same in both cases (because there is the same amount of mass inside that radius in both cases).
    Last edited by Strange; February 7th, 2013 at 10:29 AM. Reason: got the numbers wrong...
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    yes, now a bh the size of 10 sun masses must have so much power, shouldn't you actually see e=mc^2 live at work when something crosses the event horizon?

    on average the curvature is still the same, but with an area (radius of black hole) that has a much higher curvature in it.
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    Quote Originally Posted by curious mind View Post
    yes, now a bh the size of 10 sun masses must have so much power, shouldn't you actually see e=mc^2 live at work when something crosses the event horizon?

    on average the curvature is still the same, but with an area (radius of black hole) that has a much higher curvature in it.
    I'm not sure what you mean by a black hole having "power". Nothing special happens when something crosses the event horizon (except that it is no longer able to communicate with the rest of the universe).

    [I just checked and I was wrong, a black hole with the mass of the sun would have a radius of about 3km]

    A 10 solar mass black hole would have a radius 10 times as large, i.e. about 30km. My understanding is that the curvature at the event horizon of a larger black hole is less than for a smaller one. But I may well be wrong about that. I am not sufficiently familiar with the math.
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    but wouldn't that be what happens? matter at c converting into energy?
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    Quote Originally Posted by curious mind View Post
    but wouldn't that be what happens? matter at c converting into energy?
    I don't think so. As far as I know, nothing significant happens as an object falls through the event horizon. You can even find videos online with simulations of what it would look like. We don't know what the ultimate fate of matter in the black hole is, but there is nothing special about the event horizon.

    p.s. just checked: seems like my intuition was right. The larger a black hole, the less curved space-time is at the event horizon.
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    is that comparing 2 black holes curvature of different sizes, or comparing the change in curvature of say, a 10 sun mass black hole to what the suns curvature was to a 50 sun mass black hole to what that suns curvature was?
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    Quote Originally Posted by curious mind View Post
    is that comparing 2 black holes curvature of different sizes, or comparing the change in curvature of say, a 10 sun mass black hole to what the suns curvature was to a 50 sun mass black hole to what that suns curvature was?
    This is comparing two black holes of different mass: the curvature at the event horizon of the larger black hole will be less than the curvature at the event horizon of the smaller black hole.

    In both cases, the curvature will be hugely greater than the curvature at the surface of the original star. (But the curvature at the distance corresponding to the radius of the original star will be what it always was.)
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    curious mind, you appear to be under the impression that a BH is a spherical mass distribution like a planet or a star, with the event horizon being a real, tangible surface. That is not the case. The event horizon is an abstract concept, it is the boundary which separates the area from which light can escape from the one which "traps" everything forever. The actual mass of the BH is ( at least according to classical GR ) all concentrated in one point, the singularity at the center of the BH. It therefore does not make sense to talk about the "density" of a BH.

    Also bear in mind that all of this discussion is valid only for stationary black holes without electric charge and angular momentum ( called Schwarzschild Black Holes ). BHs with charge and/or momentum are much more complicated than this.
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    no, actually i think it's anything but a planet. i think it's matter converted to pure energy.
    i don't really know anything about singularity, if the BH has a radius of 500 km, what size would it be? maybe density is the wrong word, but it still has a larger curvature than what the sun had.
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    Quote Originally Posted by curious mind View Post
    no, actually i think it's anything but a planet. i think it's matter converted to pure energy.
    We don't know what happens to matter inside the black hole.

    i don't really know anything about singularity, if the BH has a radius of 500 km, what size would it be?
    What size would what be? The black hole? 500km radius. The singularity? Zero sized. That is what singularity means. (It isn't really, but until it is clearer what is being asked ...)

    maybe density is the wrong word, but it still has a larger curvature than what the sun had.
    Yes.
    Last edited by Strange; February 8th, 2013 at 04:21 AM. Reason: clarification re singularity
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    Quote Originally Posted by curious mind View Post
    no, actually i think it's anything but a planet. i think it's matter converted to pure energy.
    i don't really know anything about singularity, if the BH has a radius of 500 km, what size would it be? maybe density is the wrong word, but it still has a larger curvature than what the sun had.
    It is convention that we speak of the radius of the event horizon being the "size" of a BH, simply because nothing crossing the event horizon can ever leave again. The mass itself however is concentrated in just one point, the singularity at the center.
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    the mass? does energy have mass?
    i know that mass can be changed into energy and vise versa, but energy itself has mass?
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    I wouldn't say it has mass but it has the same gravitational effect as the equivalent mass.
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    Quote Originally Posted by Strange View Post
    I wouldn't say it has mass but it has the same gravitational effect as the equivalent mass.
    yes ok, that's how i also see it. so a black hole wouldn't need/doesn't have to have a singularity. isn't it somehow the same thing as the BB, but reversed?

    the possibility of energy to change into matter = the possibility of matter changing into energy. where we, in both cases, aren't able (yet or ever) to find the last piece of the puzzle.
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    so a black hole wouldn't need/doesn't have to have a singularity.
    Yes it does, so long as you disregard quantum effects. There is no known force in nature which can counteract the gravitational collapse beyond the event horizon, so all of the mass will collapse into a singularity.
    It's a different story once one takes into account quantum effects, though, but that's outside the remit of General Relativity.
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    Quote Originally Posted by curious mind View Post
    yes ok, that's how i also see it. so a black hole wouldn't need/doesn't have to have a singularity.
    Well the only theory we have says it has. (I don't see what the mass/energy thing has to do with that.)

    the possibility of energy to change into matter = the possibility of matter changing into energy.
    And both of these happen.

    where we, in both cases, aren't able (yet or ever) to find the last piece of the puzzle.
    Which "last piece of the puzzle"? There are probably an infinite number of "pieces" we haven't found yet (that is what makes science such fun.)
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    but you could leave the singularity out of the theory, and still have the same answer. and if both happens i.e. BB = energy to mass convertion, why you add mass (singularity) to a black hole where it is mass to energy convertion?

    last piece of the puzzle for BB/BH, we don't know how/where/why the energy came from to start all of it, and we don't know what's past the event horizon after matter turned into energy.
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    Quote Originally Posted by curious mind View Post
    but you could leave the singularity out of the theory, and still have the same answer. and if both happens i.e. BB = energy to mass convertion, why you add mass (singularity) to a black hole where it is mass to energy convertion?
    The theory predicts the singularity. It makes no difference whether matter that falls in is turned to energy or not. They have the same gravitational effect. But as far as anything outside the black hole is concerned, it doesn't make any difference if there is a singularity or the black hole is full of chocolate.

    last piece of the puzzle for BB/BH, we don't know how/where/why the energy came from to start all of it, and we don't know what's past the event horizon after matter turned into energy.
    We need a theory of quantum gravity. (But that will probably just raise more questions ...)
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    why does it predict a singularity? or how.
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    Quote Originally Posted by curious mind View Post
    why does it predict a singularity? or how.
    The maths is beyond me... Non-technically, everything falls to the center and nothing can stop it. Or, there is infinite curvature at the center.

    Anything more than that needs someone like Markus to explain!
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    you could have a continous curvature without it being nfinite, same as having space expanding without it being infinite.

    yeah, let's wait for Marcus.
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    Quote Originally Posted by curious mind View Post
    why does it predict a singularity? or how.
    You could try this.
    As I understand it (in simple terms) it's where the gravity is sufficiently strong to overcome the "strength of the materials" that make up the star, i.e. the matter itself can no longer withstand the pull inwards.
    Gravity compresses matter but, usually, it's negligible. With a BH it becomes rather less negligible - and the "compressive force" is not only greater than the mechanical strength of the material but also the internal "nuclear strength".
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    Quote Originally Posted by Dywyddyr View Post
    Quote Originally Posted by curious mind View Post
    why does it predict a singularity? or how.
    You could try this.
    As I understand it (in simple terms) it's where the gravity is sufficiently strong to overcome the "strength of the materials" that make up the star, i.e. the matter itself can no longer withstand the pull inwards.
    Gravity compresses matter but, usually, it's negligible. With a BH it becomes rather less negligible - and the "compressive force" is not only greater than the mechanical strength of the material but also the internal "nuclear strength".
    i can't help it, but reading this sounds like e=mc^2 to me. i don't see why this leads/predicts a singularity. i'll just read it again and again and again til my head either clears up or forms another question.
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    Well, if you really want to know: Schwarzschild metric - Wikipedia, the free encyclopedia

    Quote Originally Posted by curious mind View Post
    i can't help it, but reading this sounds like e=mc^2 to me.
    I'm still not sure what you are thinking of there. After all, if all the mass turned to energy (say, photons) then why wouldn't it dissipate instead of collapsing. Or, if the gravity is going to make it collapse to a point, why would chaning to energy make any difference: we know it has the same gravitational effect.
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    E=mc2?

    Okay I'll try to simplify it a bit more.
    Gravity compresses everything. The only thing that stops a planet (or other object) "collapsing" is that the material it's made of is strong enough to resist that pull, right? Think of a long thick steel beam compared to a long thin one. The thin one will collapse under its own weight, the thick one won't.
    Likewise gravity will pull material together to form a planet and the collapse/ crushing/ whatever you want to call it will stop when the compacted material has sufficient strength to resist the pull.
    If the size reduces significantly faster than the mass then, because of the equations governing gravity, mass and radius, the gravity will become so strong that each "sequential collapse" takes the new radius down to a level where the "new value" for gravity dictates that a larger radius is required to resist it - but the radius has decreased.
    It becomes a self-sustaining "reaction" - and ends when the pull of gravity is so strong that it crushes matter completely, overcoming not just the mecahnical (structural) strength, but also the internal nuclear forces.
    Then you end up with zero radius and a positive mass.
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    And, if it is crushed that far (zero size?) then the distinction between matter and energy probably becomes irrelevant.
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    Quote Originally Posted by curious mind View Post
    you could have a continous curvature without it being nfinite, same as having space expanding without it being infinite.
    yeah, let's wait for Marcus.
    Ok, I had mentioned the basic reason before already - there is a certain mass limit ( called the Tolman-Oppenheimer-Volkoff limit ) beyond which, if gravitational collapse occurs, there is no known force of nature which would be able to stop such a collapse ( for simplicity's sake I will ignore another class of stars, the quark star ). What that means is that the gravitational self interaction of the mass exceeds all other fundamental forces ( strong, weak, electromagnetic ), so that the gravitational collapse leads to only one possible outcome - a singularity. The mass of the star literally crushes itself. In almost all physical situations that will lead to a ring singularity rather than a point singularity, due to the conservation of angular momentum of the parent star. It is interesting to note that even good old Newtonian gravity already predicts black holes; they simply occur if the total mass is so great that its gravitational effects outweigh the other fundamental forces.
    It is really better not to think of a a gravitational singularity as a point of infinite curvature, but rather as a discontinuity ( a topological defect ) in space-time beyond which time-like geodesics cannot be extended further into the future - in other words, the world-lines of all infalling observers end at the singularity. The Big Bang singularity, on the other hand, is a singularity beyond which time-like geodesics cannot be extended further into the past. This answers another FAQ, namely whether the BB and a BH are the same - they are not.

    Once again, a note of caution though - this picture is valid only if one disregards quantum effects, and only under classical GR.
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    why is the only outcome a singularity, when a singularity is mass which collapsed under it's own weight? isn't it more that the gravitational collapse leaves no room for matter? yes, i haven't read anything yet and stuck at this point, but if the event horizon alone can rip apart every atom, how can there be a singularity in a black holes center?
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    Quote Originally Posted by curious mind View Post
    why is the only outcome a singularity, when a singularity is mass which collapsed under it's own weight? isn't it more that the gravitational collapse leaves no room for matter? yes, i haven't read anything yet and stuck at this point, but if the event horizon alone can rip apart every atom, how can there be a singularity in a black holes center?
    I'm sorry, but I have no idea what you are trying to say.
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    Quote Originally Posted by curious mind View Post
    why is the only outcome a singularity, when a singularity is mass which collapsed under it's own weight?
    Because there is nothing (we know of) to stop it and so it becomes infinitely compact.

    isn't it more that the gravitational collapse leaves no room for matter?
    Not sure what that means. It is the matter and energy that collapses. (Yes, it becomes zero-sized which you could say means there is "no room" for it; but we don't really know what occurs at these extreme conditions.)

    but if the event horizon alone can rip apart every atom
    That would only be true for very small black holes. The tidal forces at the event horizon of a large black would not be very strong and you could fall through the event horizon without even noticing anything special. There will be some point within the black hole where the tidal forces will become strong enough to rip things apart. But by then the temperature may be more significant. Certainly by the time it gets close to the singularity there won't still be atoms. There may not even be any particles we know. We just don't know.
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    Quote Originally Posted by Markus Hanke View Post
    so a black hole wouldn't need/doesn't have to have a singularity.
    There is no known force in nature which can counteract the gravitational collapse beyond the event horizon
    Push gravity doesn't have that problem.
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    Quote Originally Posted by bill alsept View Post
    Push gravity doesn't have that problem.
    A pretty nonsensical statement, given that you don't have a working PG model.

    By the way, there is no "problem" here at all, because, due to GR being a classical theory, the singularity happens only because we disregard quantum effects during the gravitational collapse. GR gives us a good, valid picture of space-time up to a certain point within the BH, but it does not make valid predictions for the area of the singularity itself. For that we would need a full theory of quantum gravity, which we don't have yet.

    May I remind you also that this thread is in the mainstream sections of the forum, this is not really the place for your personal theories, like PG.
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    i don't know if i got that right, in quantum theory; gr would = -?
    like over-clocking a pc and then watch it crash?
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    Quote Originally Posted by curious mind View Post
    i don't know if i got that right, in quantum theory; gr would = -?
    like over-clocking a pc and then watch it crash?
    I don't understand this post...?
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    What we can discuss here, at least big scientist or organizations do not know about this very tough psychics even I have heard them on the TV that in black hole the psychic rules doesn’t work. Few days back I read a column on news site the NASA measure the speed of wind in the center of black hole is 20 million mph.
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    Quote Originally Posted by oliverclay View Post
    Few days back I read a column on news site the NASA measure the speed of wind in the center of black hole is 20 million mph.
    Sounds thoroughly bogus to me.
    Maybe you mean this: NASA clocks 20 million mph winds near black hole.
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    Quote Originally Posted by Dywyddyr View Post
    That's marginally faster than Hurricane Sandy!
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    do we know what ratio of matter other planets in different galaxies are made of?
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    Quote Originally Posted by curious mind View Post
    do we know what ratio of matter other planets in different galaxies are made of?
    I doubt that. Since we don't have a piece of the exoplanet, we can't say for sure what it's base elements are. However, I believe it to be possible to know the ratio of exoplanet to star. Have a look at this - Planets Around Other Stars - NASA Science

    It tells of how exoplanets are found. Maybe using the wobble the star experiences, we could possibly work out the matter ratio. Anyone got a suggestion?
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    maybe the bh itself is a perfect vacuum?
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    Quote Originally Posted by curious mind View Post
    maybe the bh itself is a perfect vacuum?
    How can it be when it has mass. And probably angular momentum. And maybe even electric charge. And an event horizon. Does that sound like a vacuum (i.e. nothing)?
    Last edited by Strange; July 26th, 2013 at 01:05 PM. Reason: clarity
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    Quote Originally Posted by lerry5 View Post
    Our understanding of black hole behavior is not very complete. We know that they can be found in the center of many, if not all, large galaxies, feeding off what are called "accretion discs," basically a bunch of material swirling around a center. That material is often the result of star formation--and yet over in the Sculptor galaxy, amid lots and lots of star formation, the black hole appears to be dormant. As material falls into a black hole, it emits X-rays. NuStar is now picking up minimal X-rays from the region, indicating the black hole has gone quiet. NASA isn't really sure what's going on.
    No, NASA is not baffled as to what's going on. NASA is also not an Observatory.

    A black Hole will emit X-Rays when material falls into it. If matter does not fall into it, X-Rays won't be produced. In short, Black Holes are not Cosmic Hoovers running around sucking everything up- there is simply no matter near enough to the Black Hole in question to fall in for the time being.

    Calling it "Dormant" is misleading. Dormant implies that it's "Turned off" somehow. No, the Black Hole is exactly the same as before, it's just not currently being bombarded by dust and debris.
    That's like saying that the Earth is Dormant in between meteor showers.
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    I have a question. The mass of the primordial egg which was present before big bang would be in trillions of black holes put together. The gravity would be enormous. How then did the Big Bang occur?
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    Is it fair to say that there no actual evidence that the structure of matter still exists within a BH? And some evidence to suggest that the structure of matter can't exist within a black hole?
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    Quote Originally Posted by parag29081973 View Post
    I have a question. The mass of the primordial egg which was present before big bang would be in trillions of black holes put together. The gravity would be enormous. How then did the Big Bang occur?
    "God said, " let there be light.", its as good answer as any, for an event we can't explain and can't find any evidence concerning. NOt that we should stop trying, but at the moment this is an event of interest that science as yet has no tools to shed anylight on.
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    Quote Originally Posted by Sealeaf View Post
    "God said, " let there be light.", its as good answer as any
    Yeah.
    So is "The gruntfuttock was having a bad hair day".
    You're still left with the fact that neither answer provides an explanation that is of any use.
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    Mr duck, would you define the word "explanation". I think you are using it in special way.
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    Quote Originally Posted by parag29081973 View Post
    I have a question. The mass of the primordial egg which was present before big bang would be in trillions of black holes put together. The gravity would be enormous.
    The difference is that a black hole consists of a concentration of mass in space. The early universe was hot dense and pretty much homogeneous, therefore the gravitational potential was the same everywhere; not the conditions to create a black hole.

    How then did the Big Bang occur?
    Space expanded (as appears to be its natural tendency).
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    Quote Originally Posted by Sealeaf View Post
    Mr duck, would you define the word "explanation". I think you are using it in special way.
    Oh, absolutely I'm using it in a special way.
    Specifically this way:
    A statement or account that makes something clear.

    You may have come across that particular special meaning of the word at some point in your life.

    Your "explanation" - "God said, " let there be light.", its as good answer as any" not only doesn't make it clear (as to why/ how the BB occurred) it also adds another level of confusion: what is god, how did he do it (i.e. what process allowed a simple phrase to effect such a large result) etc.

    You'll also note (please) that I wrote "neither answer provides an explanation that is of any use".
    Ideally (and from a professional and personal point of view) an explanation should have some actual utility - i.e. it can be applied, used as a start point for further exploration (which leads to further explanation 1), checked...
    Goddidit is a dead end, and unverifiable, as far as "explanations" go. It's predicated on an unevidenced assumption.


    1 Still using my "special meaning" of the word.
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    Can someone explain please how can black holes swallow photons when they are massless ?
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    Quote Originally Posted by laza View Post
    Can someone explain please how can black holes swallow photons when they are massless ?
    Light is affected by gravity despite the fact that it has no mass. (This is even true in Newtonian gravity.)

    In general relativity, it comes down to the fact that what we perceive as "gravity" is actually the curvature of space-time. Photons always travel in "straight lines" but in the presence of mass, a "straight line" is actually a curve (called a geodesic - like the shortest distance on the surface of a sphere is a great circle). Near a black hole, even photons travelling at the speed of light have their paths curved towards the black hole and, once they get close enough they cannot avoid falling in. Once inside the black hole, all paths lead towards the singularity. There is no direction which is "out".
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    Photons are subject to gravitation. Photons always travel along the geodesic, and gravity warps space/time, and hence warps the geodesic. When the geodesic is bent sufficiently, as within the Event Horizon, then the photon can never exit the EH.
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    Quote Originally Posted by Strange View Post
    Light is affected by gravity despite the fact that it has no mass. (This is even true in Newtonian gravity.)
    But note that Newtonian gravity gives the wrong answer for the amount that light is affected by gravity.
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