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Black holes are confusing!
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21 / M / Severn
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Posted 1/19/13
Read a definition of a black hole, which stated that a black hole is a incredibly massive object that doesn't take up space. :crazy:

Can someone help me understand this because how can it not have any volume??

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34 / M / The Void.
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Posted 1/19/13 , edited 1/19/13
It takes up space as far as I know. Where did you get this definition?
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44 / M / Memphis, TN
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Posted 1/19/13 , edited 1/19/13
Heck, I thought they warped and then devoured the surrounding space (and the stuff in it). . .
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19 / M
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Posted 1/19/13
Hole..
mipegg 
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22 / M / England
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Posted 1/19/13
The concept is really quite simple. In a star you have balancing forces, the radiation pressure acting in an outwards direction and the gravitational forces acting inwards (it is actually more complex than that involving some lovely entropy and electrodynamic forces, but thosea re really not needed for the basic understanding).

The radiation pressure comes from the centre of the core where fusion happens, in stars there is really 1 major cycle of fusion goes on

Proton+Proton bang into eachother from all the energy they have due to the heat/pressure of the core, the strong nuclear force takes over and binds them together

Whilst the P-P (proton proton) interaction is taking place one of those protons has to beta decay into a neutron, throwing out a positron (an electron with +e rather than -e charge basicaly) and a neutrino (just a weird partcile)

This forms a deuteron, a different type of hydrogen with 1 proton and 1 neutron

A proton and a deuteron then bang into eachother to make Helium 3 (2 protons and 1 neutron) kicking out a gamma ray

2 Helium 3's then bang into eachother to form Helium 4 (2 protons 2 neutrons) kicking out 2 protons.

The first step is the really hard one to do (theres ap retty low chance of the beta decay happening whilst 2 protons are near enough to fuse) but luckily there are lots of protons in the sun so it actually works out.

The net result of the whole thing is that we get a few particles carrying off 'spare' energy, this mostly goes off in the neutrino, positron and gamma ray(s). Since the actual burning core is quite small the net effect is these all emanate outwards.

Gravitational force is pretty simple, the entire mass of gas is trying to fall inwards, it cant do it since there is the radiation balancing it. Now, when the star comes to an end its fusion stops and all of a sudden you have no balance between radiation pressure and gravity, the net effect is it keeps getting smaller and just stops existing in typical space. (I skipped alot of steps here).

As for the mass of a blackhole, it has no more mass than the star which made it. It isnt some super duper rape machine in space, a 1 stellar mass blackhole has the exact same gravitational attraction as a 1 stellar mass star.

As for it taking up 'space' the it simply cant do that because of how distorted space is in its sphere of influence, there is the event horizon which has a radius but thats not actually the black hole, it would be like saying the edge of the solar system is part of the sun since you can measure solar winds out there.
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21 / M / Florida
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Posted 1/19/13
Black holes do take up space. They can be either big or small, can be the size of an atom or bigger than a sun.
mipegg 
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22 / M / England
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Posted 1/19/13

elementg12 wrote:

Black holes do take up space. They can be either big or small, can be the size of an atom or bigger than a sun.


No, the blackhole itself has no size. The event horizon will be different but thats not actually the blackhole
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21 / M / Florida
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Posted 1/19/13 , edited 1/19/13
How can a black hole have mass but no size? It isn't an actual hole.
mipegg 
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22 / M / England
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Posted 1/19/13 , edited 1/19/13

elementg12 wrote:

How can a black hole have mass but no size? It isn't an actual hole.


Thats the very definition of a blackhole. The single point at which the gravitation curvature tensor becomes infinite, this only happens at precisely 1 point therfor has no size, the real question should be why does everything have to occupy a space? In the same vane look at light, light has no size, occupies no space yet is clearly a physical thing. How can that possibly work? Its all to do with the slightly odd effects of relativity, mathematically it is all perfectly fine, just a bit odd when you hear it without seeing the derivations.

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21 / M / Florida
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Posted 1/19/13 , edited 1/19/13
Well we will just have to agree to disagree.
Any object with a physical radius smaller than its Schwarzschild Radius is considered a Black Hole. So it has to take up space if its a physical object so i don't get what you re saying.
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94 / M / Pennsylvania
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Posted 1/19/13
best science class ever
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23 / M / Hughesville, Penn...
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Posted 1/19/13
There is already a thread on black holes in extended discussion, so you should probably delete this.
mipegg 
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22 / M / England
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Posted 1/19/13

elementg12 wrote:

Well we will just have to agree to disagree.
Any object with a physical radius smaller than its Schwarzschild Radius is considered a Black Hole. So it has to take up space if its a physical object so i don't get what you re saying.


Then tell me, what is the size of light? Additionally the schwarzschild radius is simply the lower limit for blackhole compression, beyond the limit something will compress itself into a blackhole, not instantly be a blackhole...
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21 / M / Florida
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Posted 1/19/13
I never said anything about the size of light. The reason light cant escape a black hole is because when it goes into one and hits the other side of the event horizon light will follow space time and bend in on itself. So light isn't getting sucked in, its just traveling into it on its own. And im not gonna reply anymore because neither of us are gonna agree with each other.
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F / Urban South
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Posted 1/19/13 , edited 1/19/13
Mipegg is correct and gave a succinct, accurate explanation. A black hole having no volume despite being massive sounds like a non sequitur because most people are accustomed to thinking of space as static rather than warpable. In actually, space-time is warped by speed and gravity (which is really just a force that can create velocity).

Imagine a whirlpool created by draining a full bathtub. If you think of space-time like it is being drawn in towards a black hole like water is pulled toward the drain, then black holes seem a little less abstract. This visualization is not really accurate, but does give you an idea of how black holes warp space-time to the extent where they don't actually occupy it. Instead, space-time bends around a black hole similar to the way a whirlpool bends around the center of a drain.


Also, when you compare a black hole to a whirlpool, all of a sudden wormholes (tunnels through space-time) seem pretty reasonable.

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