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Thread: Where does all that matter go?

  1. #1
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    Where does all that matter go?

    I read the black hole faq sticky, but it doesn't seem to answer my questions about black holes.

    I'm curious to know where all the matter that gets sucked into a black hole goes. And also what exactly is a singularity? I've only heard of these things on star trek before I read the faq.

    Any insight would be helpful thanks!

  2. #2
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    A singularity is where God divides by zero.

    Seriously, the bottom line is that if you get enough matter scrunched up in one place, it will compact together under the force of gravity such that - according to our present understanding of physics - nothing will stop it from continuing to compact. So the assumption is that it contracts to a point of infinite density. But then all the equations break down, so there's no way of saying what really "happens" to the matter. We don't know. All we can say is that the gravitational force associated with the matter is still emanating from that point.

    Some of the physicists on here will probably come up with a more accurate or comprehensive explanation, but that's the way I understand it right now.
    Everything I need to know I learned through Googling.

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    Thanks again ToSeek!

    So you're saying that a singularity is pretty much just a name for the unknown?

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    Yeah. The matter just stays there, but very, very compacted.

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    Quote Originally Posted by dvb
    Thanks again ToSeek!

    So you're saying that a singularity is pretty much just a name for the unknown?
    A very, very massive unknown.

    Well, I hate saying just "unknown," because that's a little too open. It's a large mass concentrated at a point that can theoretically exist based on general relativity. But I think it's fair to say that we really don't know what happens there or if any truly exist - perhaps there is some physics we don't know about that stops the compaction before we get to the "divide by zero" stage.

    Again, I'm not a trained physicist, just an interested layperson, so take all this with a grain of salt.
    Everything I need to know I learned through Googling.

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    Quote Originally Posted by dvb
    So you're saying that a singularity is pretty much just a name for the unknown?
    A singularity is the name for something that has no volume. It's just a single point. Singular as in single.

    Consider this, if you had a quantity of hydrogen gas it would expand as gases tend to do and you'd lose it. If you kept it in a balloon, it'd expand and push against the sides of the balloon. If you had a lot more H2, you'd just need a bigger balloon. Right? But if you had a incredibly tremendously huge about of hydrogen, you'd have Jupiter. There isn't much else in jupiter than plain old H2. There's just so much of it that it's held together under it's own gravity.

    Jupiter is just Hydrogen, but it can't expand out into space because of it's own gravity. Gravity keeps the gas together, but what stops it from collapsing down to a much smaller volume? The answer is electromagnetism. The electromagnetic force in between individual atoms of hydrogen resists the crushing force of gravity. So the H atoms deep inside Jupiter are pressed together by gravity, but held apart by electromagnetism, and they support all the atoms above them - just like the columns of a building support the floors above.

    What happens in a black hole is that something transpires that allows gravity to overcome electromagnetism. When that happens, it's like cutting out the support columns in a building. To use a particularly morbid example, think of the WTC in New York. The planes hit a certain floor and the fuel that spilled out eventually melted the supporting structure for that floor. When that happened, the floors above fell a distance of *just one floor* Say about five meters. That's all that happened. It would have stopped right there, but when those floors fell that short distance, they picked up enough momentum to break the support structure of the next floor, and they fell another 5 meters, and broke the support of that floor, etc etc.

    So imagine something happened to the atoms at the center of Jupiter so that they could no longer support the atoms above them. They'd collapse together very tightly. All the atoms above would fall inward and repeat the process. Unlike the WTC, which collapsed into a pile of rubble, there's nothing to stop the collapse of a black hole. It just keeps falling in on itself forever, theoretically. The volume gets smaller and smaller and the density goes up.

    That's a singularity. Zero volume and infinite density.

    If you've managed to read this far, you probably wonder what happens to cause the support columns to fail in the first place. As far as I know, the only thing known to cause a black hole is the violent explosion of a very large star, an even known as a supernova.

    A couple of other things: I know Jupiter has some kind of metallic core. Otherwise it wouldn't have a magnetic field. Also, I don't mean to suggest that Jupiter could collapse into a black hole. It doesn't have enough mass.

    The question was asked, what happens to mass that falls into a black hole (please say falls in rather than sucked in). I've read that in most cases matter that falls in goes into orbit. It may be in orbit beneath the event horizon, so you'll never see it again, but it is still in orbit. But hey, I'm no expert so I'm sure someone will correct me if I'm wrong.

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    Thank you very much everyone!

    tofu, your explanation was excellent. It makes sense that all the matter could just be orbiting around inside the event horizon since the light of that matter will never escape, and we'd never know. So from what I understand now, a black hole really isn't a hole at all. It's just something we can't see unless matter is falling into it from outside the event horizon.

    This makes me wonder now. You say that a black hole, which is a singularity has no volume to it. How can we measure that there's no volume to it when nothing can escape from it and we can't see past the event horizon? Maybe it just appears to have no volume because of the way it warps space-time in all directions, or maybe I'm wrong. lol

    Any help would be appreciated.

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    Quote Originally Posted by dvb
    How can we measure that there's no volume to it when nothing can escape from it and we can't see past the event horizon?
    We don't measure the volume.

    Here's the thing. Well established and experimentally observed physics tells us that electromagnetism keeps things, pretty much anything including the Earth, Jupiter, the Sun, everything, from collapsing indefinitely under its own gravity. Ok?

    So then someone asked what would happen if gravity was so strong that it overcame electromagnetism. The answer they came up with was that the object would then collapse into... nothing. If electromagnetism was overcome, there was no longer anything to stop the collapse. So logically, it collapses into zero volume.

    The original name for such an object was “a gravitationally completely collapsed object.” And it was just a theory. Nothing more. Astronomers and physicists thought a lot about the theory and eventually realized that if such an object existed, there were ways they could detect it. So, using only the theory to guide them, they went looking. Low and behold they started finding them.

    Nobody has ever measured the volume. They started with a theory that said “if it's possible for gravity to overcome electromagnetism, I predict the following” one of those predictions is that a singularity has no volume. The other predictions have been observed, so that's strong evidence that the theory is correct and therefore the other predictions are true as well. We can get to this conclusion without ever measuring the volume.

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    Quote Originally Posted by tofu
    So then someone asked what would happen if gravity was so strong that it overcame electromagnetism. The answer they came up with was that the object would then collapse into... nothing. If electromagnetism was overcome, there was no longer anything to stop the collapse. So logically, it collapses into zero volume.
    I'm going to picky and make a small correction (hopefully, tofu won't mind ). Electromagnetic repulsion keeps the atoms of normal matter spaced as we see them. For a large amount of matter (say, a white dwarf star), this electric repulsion is already no longer sufficient. What keeps it from collapsing further is "electron degeneracy pressure" (essentially, the Pauli exclusion principle that no two electrons can be in the same energy state, so they can only get so close together). For a slightly larger amount of mass (above about 1.4 solar masses) the pressure is high enough that the electrons combine with the protons, forming neutrons, and it's now neutron degeneracy pressure that halts the collapse (this is a neutron star). If there's more mass than neutron degeneracy can support, then it collapses to a black hole as far as we know, because as far as we can tell there isn't anything else that could prevent further collapse.

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    Wow, very deep. Thank you both!

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    Layman speaking: am I mistaken in saying that given enough time - a long, loooong time - the matter that falls into a black hole eventually gets out, in the form of Hawking radiation?

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    Quote Originally Posted by informant
    Layman speaking: am I mistaken in saying that given enough time - a long, loooong time - the matter that falls into a black hole eventually gets out, in the form of Hawking radiation?
    No. That is, you are not mistaken, at least according to our current models. Got to be careful with those questions phrased in the negative.

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    Quote Originally Posted by tofu
    ...Nobody has ever measured the volume. They started with a theory that said “if it's possible for gravity to overcome electromagnetism, I predict the following” one of those predictions is that a singularity has no volume. The other predictions have been observed, so that's strong evidence that the theory is correct and therefore the other predictions are true as well. We can get to this conclusion without ever measuring the volume.
    The singularity may also have no location in space. The black hole and its event horizon certainly have a coordinate and location, but once we are at the singularity, where time and space end, perhaps there is a transformation.

    The black hole's singularity could also be thought of as a mathematical precept within our physics and math. An "understudy" for what is actually there. Perhaps the singularity is analogous to a Mandelbrot set. A compression into a dual identity, at one and the same with a larger space that is the same location. Akin to the fractal images that shrink to reveal themselves to be part of the same image at it's largest, while shrinking to become again the same image. #-o

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    Quote Originally Posted by tofu
    The original name for such an object was “a gravitationally completely collapsed object.” And it was just a theory. Nothing more. Astronomers and physicists thought a lot about the theory and eventually realized that if such an object existed, there were ways they could detect it. So, using only the theory to guide them, they went looking. Low and behold they started finding them.
    To nitpick a little, what astronomers have found are highly massive objects (i.e., sources of significant gravitational force) with what appears to be an event horizon. We have no way of knowing what goes on inside the event horizon: all we can say for sure is that there is x amount of mass inside there (where x is a big fat number). Theory tells us that most of the x is in a singularity (for the reasons that Grey explains), but there's no way of proving that observationally right now.
    Everything I need to know I learned through Googling.

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    Quote Originally Posted by Grey
    If there's more mass than neutron degeneracy can support, then it collapses to a black hole as far as we know, because as far as we can tell there isn't anything else that could prevent further collapse.
    Grey's right. Of course, just because we don't know of any mechanism that could prevent further collapse doesn't mean there might not be such a mechanism. In fact, realistically this singularity idea presents us with a major breakdown of our ability to make sense of our surroundings. As Harvard GR prof. Rothman says,

    ...a singularity.... is a much more serious breakdown than a flat tire or a cracked engine block. It is, in fact, a physical impossibility -- a region where the laws of physics break down altogether and even spacetime comes to an end.
    Problem is, we can't just look inside and see what the heck is going on!

    But obviously the mass is still there because its gravity still affects its surroundings. So this idea of a black hole as a wormhole "transport" to another universe or another location within our universe would seem little more than science fiction.
    Everyone is entitled to his own opinion, but not his own facts.

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    I've always had the problem with the singularity being a mass with zero volume... is this just a simplification for the equations? Because I can't imagine the mass reaching zero volume in anything less than infinite time. :-?

    Hell, it's meant to be confusing, it's a black hole, it messes with relativity in crazy ways.

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    Quote Originally Posted by Cougar
    Problem is, we can't just look inside and see what the heck is going on!

    But obviously the mass is still there because its gravity still affects its surroundings. So this idea of a black hole as a wormhole "transport" to another universe or another location within our universe would seem little more than science fiction.
    Maybe it leads into fluidic space where everything is matter.

    Seriously though, it all seems hopeless to ever be able to explore a black hole. If we could perfect teleportation, we might be able to beam our bodies into the black hole, but we'd need to find some way to rematerialize on the other end.

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    Or how about a wormhole that has one end inside a black hole's event horizon? I bet that would cause a few mathematical headaches.

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    Quote Originally Posted by informant
    Layman speaking: am I mistaken in saying that given enough time - a long, loooong time - the matter that falls into a black hole eventually gets out, in the form of Hawking radiation?
    Yes and no! As Hawking said; "A black hole has no hair", meaning that all we know about a black hole is its mass, charge and spin. Anything that enters a black hole loses all individual identifuing characteristics. The particles of Hawking radiation are created at the event horizon from the gravitational energy of the black hole. So, while a black hole loses mass by Hawking radiation, technically, it is not the same matter that went in.

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    If there's more mass than neutron degeneracy can support, then it collapses to a black hole as far as we know, because as far as we can tell there isn't anything else that could prevent further collapse.
    Well, there is also the possibility of quark degeneracy.

    http://www.nature.com/nsu/020408/020408-8.html

    Astronomers think they might have spotted a quark star, a mass of fundamental particles only a few kilometres across but weighing more than our Sun. If the star's nature is confirmed, it would be the first example of this state of matter.
    I would like to note that that neutron and quark degeneracy relate to the quantum mechanical explanation for black holes. There is also a relativistic explanation for black holes that says, in essence, that when you move past the Schwartzchild radius, time and distance effectively flip so that movement forward in time effectively becomes movement inwards towards the singularity. So regardless of any other possible degeneracy forces that might exist, once matter (or energy) passes the event horizon, it moves inevitably towards the singularity.

    For a better explanation of this than I can give, check the link from JREF and look towards the bottom for a post by Ziggurat.

    http://www.randi.org/vbulletin/showt...p;pagenumber=2

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    Quote Originally Posted by Kaptain K
    Quote Originally Posted by informant
    Layman speaking: am I mistaken in saying that given enough time - a long, loooong time - the matter that falls into a black hole eventually gets out, in the form of Hawking radiation?
    Yes and no! As Hawking said; "A black hole has no hair", meaning that all we know about a black hole is its mass, charge and spin. Anything that enters a black hole loses all individual identifuing characteristics. The particles of Hawking radiation are created at the event horizon from the gravitational energy of the black hole. So, while a black hole loses mass by Hawking radiation, technically, it is not the same matter that went in.
    Black holes also have a temperature, which was puzzling to physicists until Hawking figured out his eponymous radiation.
    Everything I need to know I learned through Googling.

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    Quote Originally Posted by Cougar
    !

    But obviously the mass is still there because its gravity still affects its surroundings. So this idea of a black hole as a wormhole "transport" to another universe or another location within our universe would seem little more than science fiction.
    Cougar, I think you have this part wrong. It is my understanding that the a "white hole" is not prohibited. The huge gravitational energy generated (outside the event horizon) as the black hole forms, is able keeps the hole intact without the mass. In other words, once the event horizon is formed, the hole no longer need the mass (which makes sense if you think about it as nothing inside the hole can get out). If anyone (Grey, Tim, Kilopi, ) out there has more info, I would appreciate a correction.


    edited for spelling

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    Quote Originally Posted by Tensor
    The huge gravitational energy generated (outside the event horizon) as the black hole forms, is able keeps the hole intact without the mass. In other words, once the event horizon is formed, the hole no longer need the mass (which makes sense if you think about it as nothing inside the hole can get out).
    I thought the event horizon was just a perimeter around the black hole where the point of no return is. I didn't realize it was something that was formed in some way or another.

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    Quote Originally Posted by dvb
    Quote Originally Posted by Tensor
    The huge gravitational energy generated (outside the event horizon) as the black hole forms, is able keeps the hole intact without the mass. In other words, once the event horizon is formed, the hole no longer need the mass (which makes sense if you think about it as nothing inside the hole can get out).
    I thought the event horizon was just a perimeter around the black hole where the point of no return is. I didn't realize it was something that was formed in some way or another.
    dvb, very simplified, there was no event horizon around the star before and there is an event horizon around a black hole. Think of it this way, as the mass shrinks, space curves more and more until there is an event horizon. The growing curvature of spacetime is how the event horizon forms.

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    Tensor

    Thank you for clarifying. My feable mind is still learning.

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    Quote Originally Posted by dvb
    Tensor

    Thank you for clarifying. My feable mind is still learning.
    Hardly feeble, you are asking good questions on things you don't understand and seem to grasp the answers, which puts you way ahead of some others that have posted here.

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    Quote Originally Posted by dvb
    Tensor

    Thank you for clarifying. My feable mind is still learning.
    Stick with it dvb - learning is all us feeble minds can do! Besides, your questions have been interesting.

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    Thank you both!

    I like to RTFM before asking questions so I don't annoy people. I know how it can be helping people with computers all the time. Learning is something I enjoy very much.

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    Quote Originally Posted by Kaptain K
    Quote Originally Posted by informant
    Layman speaking: am I mistaken in saying that given enough time - a long, loooong time - the matter that falls into a black hole eventually gets out, in the form of Hawking radiation?
    Yes and no! As Hawking said; "A black hole has no hair", meaning that all we know about a black hole is its mass, charge and spin. Anything that enters a black hole loses all individual identifuing characteristics. The particles of Hawking radiation are created at the event horizon from the gravitational energy of the black hole. So, while a black hole loses mass by Hawking radiation, technically, it is not the same matter that went in.
    I read over all the posts again and seemed a little puzzled at this. If hawking radiation doesn't come from matter that fell into the black hole, then where could it have come from? Another dimension perhaps? And how can we prove that the matter isn't transformed into energy in the form of hawking radiation and expelled from the event horizon? Is there an imbalence of matter to energy that could prove why it's not?

    Edit: sorry, I didn't read all of that correctly. The hawking radiation comes from gravitational energy. But you need matter to have gravity. So it would seem to me that the matter falling into the black hole creates a bigger gravitational field, which is then expelled in the form of hawking radiation. In an indirect way, it still seems that the matter going in still has is expelled in some way in the form of hawking radiation.

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    Quote Originally Posted by dvb
    I read over all the posts again and seemed a little puzzled at this. If hawking radiation doesn't come from matter that fell into the black hole, then where could it have come from? Another dimension perhaps?
    The radiation is created outside the black hole during virtual particle creation.


    Quote Originally Posted by dvb
    Edit: sorry, I didn't read all of that correctly. The hawking radiation comes from gravitational energy. But you need matter to have gravity.
    You need energy to have gravity (remember mass-energy equivilance or E=Mcc). Normally, pairs (particles and antiparticles) of virtual particles borrow energy from space, become real particles, and almost immediately anihilate each other, returning the energy back. This is allowed by the Uncertainty Priciple of Quantum Mechanics. Near the black hole, when the particles are created, one can fall into the black hole and the other 'escapes' from the black hole. Since they can't anihilate each other as they normally would, they have to stay as real particles. But the escape of the real particle reduces the mass of the black hole (because the particle "borrowed" the energy from the black holes gravitational field).

    Quote Originally Posted by dvb
    So it would seem to me that the matter falling into the black hole creates a bigger gravitational field, which is then expelled in the form of hawking radiation. In an indirect way, it still seems that the matter going in still has is expelled in some way in the form of hawking radiation.
    Well, in an inderect way, yes it is expelled. But it is no longer the same matter that fell into the black hole.

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