Exploring the Phenomenon of Black Holes: Gravity and Temperature at the Center

[cragar]

if u were at the center of a black hole which way would the gravity pull u. if it pulled u at all.
what do u guys think.

Another question is temperature relative . like if i had something on Earth near absolute zero
but relative to the sun its kinetic energy would be different.
And how do scientist's know were absolute zero is if they can't get to it how do they know its not further than they think.

 

[HallsofIvy]

If you are at the center of a uniform sphere of any density, the net gravitational force on you would be 0. That is because the force due to the mass in any direction is canceled by equal force in exactly the opposite direction.

As far as absolute 0 is concerned, it is not to difficult to measure the volume of a fixed amount of gas at two different temperatures (at the same pressure), determine the linear function (PV= NRT) giving those two points and then solve for the T that makes V= 0.

 

[cragar]

so then would u be weightless.

 

[fluidistic]

so then would u be weightless.

Not really. If you could keep your body's proportions and that the black hole is larger than your body, the center of the black hole if it has a center is inside your body, then only one millimeter apart from the center of the black hole would be attracted toward the center of the black hole. It is of course a totally impossible scenario.

 

[cragar]

y is this an impossible scenario , what if a photon was at the center.

 

[Danger]

Since no matter can actually exist at the singularity, the question is irrelevant. For any living organism, the tidal forces alone would rip it to shreds long before contact with the centre.

edit: Oops, Cragar... I just realized that this might have been taken as a response to your last post. Not so; it was aimed at the original.

 

[fluidistic]

y is this an impossible scenario , what if a photon was at the center.

I was talking about a human into a black hole. I don't know enough Physics to answer your question, but I know that a human wouldn't survive, wouldn't conserve its proportions and I believe a black hole is smaller than a human body, but I'm not sure of the later.

 

[cragar]

they have super massive black holes that are like 10^6 times bigger than our sun.

can a photon exist at the singularity?
And how would time behave at the singularity taking gravitational time dialtion into effect

 

[Archosaur]

they have super massive black holes that are like 10^6 times bigger than our sun.

Careful.

They are 10^6 times more massive than our sun.

 

[cragar]

but certainly large enough for a photon to be in the center.

 

[DaveC426913]

Simply put, the laws of physics as we know them break down at the singularity. We do not know what happens there. This is the only meaningful answer to your question.

 

[cragar]

ok thanks for your answer

 

[stevebd1]

cragar, you might want to take a look at rotating black holes.

 

[klite]

I believe a black hole is smaller than a human body, but I'm not sure of the later.

You mean a black hole or the singularity? A black hole: the more mass it has, the more space it takes up (I think you mean how much space it takes up). For example, a black hole with the mass of our sun would be about 2 miles in radius. A typical black hole has a ten solar mass, and therefore a radius of about 12.5 miles. A million solar mass black hole (like at the center of a galaxy) would have a radius of 2,000,000 miles.

A singularity: Technically, the size of a singularity is zero, according to classical physics. It is just a point, and the laws of physics end at the event horizon. Our physics stop working when you get down to a certain length (Planck length). There is no way of knowing.

 

[DaveC426913]

You mean a black hole or the singularity? A black hole: the more mass it has, the more space it takes up (I think you mean how much space it takes up). For example, a black hole with the mass of our sun would be about 2 miles in radius. A typical black hole has a ten solar mass, and therefore a radius of about 12.5 miles. A million solar mass black hole (like at the center of a galaxy) would have a radius of 2,000,000 miles.

For further clarification: This dimension refers to the event horizon, which is merely an abstract value representing the distance from the black hole - closer than which light cannot escape.

There is no physical object that delineates this boundary.

 

[MeJennifer]

if u were at the center of a black hole which way would the gravity pull u. if it pulled u at all.
what do u guys think.

Another question is temperature relative . like if i had something on Earth near absolute zero
but relative to the sun its kinetic energy would be different.
And how do scientist's know were absolute zero is if they can't get to it how do they know its not further than they think.

A black hole has no center.

 

[Ookke]

Just wondering: is the singularity black, when seen inside event horizon?

Does the "light cannot escape" apply only to event horizon (light from inside cannot cross the event horizon), but inside event horizon of a giant black hole we could actually see the singularity?

 

[cragar]

A black hole has no center.

So a black hole has no center of mass.

 

[Archosaur]

It does. All you need to have a center of mass is mass.

If you are a singularity, your center of mass (a point) is "co-pointal" with you.

 

[George Jones]

Just wondering: is the singularity black, when seen inside event horizon?

Images that we see are from the past. For example, we the Sun as it was 8 minutes ago. The singularity of a spherical black hole is in the future, so we don't an image of it.

 

[qraal]

Images that we see are from the past. For example, we the Sun as it was 8 minutes ago. The singularity of a spherical black hole is in the future, so we don't an image of it.

All the current work on black-hole singularities makes that idea of space being rotated into a time direction seem dubious. According to work by Igor Novikov the inner singularity, after it has formed and settled down, should be traversable with a finite impulse from the tidal forces. Even though the strength of the tide goes to infinity, the total energy a body experiences from it is probably finite. A big enough black-hole's singularity might even be survivable by a human.

 

[Chronos]

The center of a black hole is a singularity, your body is not a singularity. The spagetti left from your transit throught the event horizon would be crushed out of existence.

 

[qraal]

The center of a black hole is a singularity, your body is not a singularity. The spagetti left from your transit throught the event horizon would be crushed out of existence.

As I've noted, depends on the singularity and just how its tidal forces change with radial distance.

 

[MeJennifer]

All the current work on black-hole singularities makes that idea of space being rotated into a time direction seem dubious. According to work by Igor Novikov the inner singularity, after it has formed and settled down, should be traversable with a finite impulse from the tidal forces. Even though the strength of the tide goes to infinity, the total energy a body experiences from it is probably finite. A big enough black-hole's singularity might even be survivable by a human.

It must be me, but this sounds like complete hogwash to me.

 

[Division]

All the current work on black-hole singularities makes that idea of space being rotated into a time direction seem dubious. According to work by Igor Novikov the inner singularity, after it has formed and settled down, should be traversable with a finite impulse from the tidal forces. Even though the strength of the tide goes to infinity, the total energy a body experiences from it is probably finite. A big enough black-hole's singularity might even be survivable by a human.

Anything that gets close to the singularity of a black hole is instantly torn appart beyond recognition.

 

[DaveC426913]

Anything that gets close to the singularity of a black hole is instantly torn appart beyond recognition.

That is the prevailing hypothesis, yes. qraal is pointing out that Novikov is suggesting there may be more to it than that.

 

[Wallace]

What MeJennifer is saying is that in technical terms, r=0 is 'not part of the manifold' in the space-time solution for a black hole. Put more simply (and less correctly) this means that you can't, as suggested by others, talk sensibly about what happens 'at the singularity' since nothing can be at the singularity, since it has zero volume.

The really important point is, again as other have stated, that this is the property of the black hole solution in GR and this theory is almost certainly inadequate, and a better theory would not go singular. It is really important to stress that a singularity is not a physics thing it is just a mathematical property of a particular solution to general relativity, which probably suggests that the theory is incomplete.

Everytime someone talks about something happeing 'at the central singularity of a black hole' a logic fairy dies It's equivalent to asking what happens to your bedroom if you divide it by zero...

 

[George Jones]

All the current work on black-hole singularities makes that idea of space being rotated into a time direction seem dubious.

Inside the event horizon, space doesn't get rotated into a time direction, it's just that human-chosen labels (coordinates) have names (chosen by humans, not by nature) that are very misleading. See

https://www.physicsforums.com/showthread.php?p=1146536&highlight=bridge#post1146536.

According to work by Igor Novikov the inner singularity, after it has formed and settled down, should be traversable with a finite impulse from the tidal forces. Even though the strength of the tide goes to infinity, the total energy a body experiences from it is probably finite. A big enough black-hole's singularity might even be survivable by a human.

It must be me, but this sounds like complete hogwash to me.

Nope.

Anything that gets close to the singularity of a black hole is instantly torn appart beyond recognition.

graal is not referring to the "central" crushing singularity, graal is referring to the weak singularity at the inner (Cauchy) horizon of roating and electrically charged black holes. Seminal work on this was done by Poisson and Israel, and this work was continued by Ori. See

http://physics.technion.ac.il/~school/Amos_Ori.pdf ,

particularly pages 15, starting at "Consequence to the curvature singularity at the IH: (IH = Inner Horizon), 16, and 24.

For Novikov's take on this, see

http://arxiv.org/abs/gr-qc/0304052.

Roughly, if components of g (the metric) are continuous but "pointy" (like the absolute value function), then first derivatives of g have step diiscontinuities (like the Heaviside step function), and second derivatives of g (used in the curvature tensor) are like Dirac delta functions. If a curvature singularity blows up like a Dirac delta function, then integration produces only a finite contribution to the tidal deformation of an object, which, if the object is robust enough, it can withstand.

 

[Ultrastar 1]

''if u were at the center of a black hole which way would the gravity pull u. if it pulled u at all.
what do u guys think.''

Inside a black hole, there is a circular structure. This structure is the collapessed core of a star. So, gravity will most likely pull toward the core, then it would circulate around the core and then back out of the singularty.

 

[Ultrastar 1]

Images that we see are from the past. For example, we the Sun as it was 8 minutes ago. The singularity of a spherical black hole is in the future, so we don't an image of it.

Wow. That never occurred to me. Thanks for the info.

 

[qraal]

graal is not referring to the "central" crushing singularity, graal is referring to the weak singularity at the inner (Cauchy) horizon of roating and electrically charged black holes. Seminal work on this was done by Poisson and Israel, and this work was continued by Ori. See

http://physics.technion.ac.il/~school/Amos_Ori.pdf ,

particularly pages 15, starting at "Consequence to the curvature singularity at the IH: (IH = Inner Horizon), 16, and 24.

For Novikov's take on this, see

http://arxiv.org/abs/gr-qc/0304052.

Roughly, if components of g (the metric) are continuous but "pointy" (like the absolute value function), then first derivatives of g have step diiscontinuities (like the Heaviside step function), and second derivatives of g (used in the curvature tensor) are like Dirac delta functions. If a curvature singularity blows up like a Dirac delta function, then integration produces only a finite contribution to the tidal deformation of an object, which, if the object is robust enough, it can withstand.

Thanks George. That's what I meant. Though he has interesting things to say about non-spinning BHs too.

 

[Chronos]

Wallace is correct. Game over when you reach the event horizon of a black hole.

 

[MeJennifer]

The really important point is, again as other have stated, that this is the property of the black hole solution in GR and this theory is almost certainly inadequate, and a better theory would not go singular. It is really important to stress that a singularity is not a physics thing it is just a mathematical property of a particular solution to general relativity, which probably suggests that the theory is incomplete.

Well, to rock the boat just a little bit, is that definably true?

For instance many solutions that have a singularity have an asymptotic flatness assumption. If a spacetime is almost flat far away from the possible black hole or even negligibly curved then the singularity may never form. And then there is the assumption of a point mass. To my thinking general relativity might imply a non-local notion of energy-momentum, so yes if we force the thing to be a point then perhaps we should not be surprised we get a singularity.

 

[Wallace]

We don't 'force' the centre of a black hole to be a point, physics does. Once the Schwarzschild radius of a body is greater than the radius of that body then all null future null paths of all points within the body end up at r=0, hence collapse to a 'singularity' is inevitable, given GR. We can also, noting other known physics, work out the stages of collapse of a dense object before it gets to this run-away collapse. For instance at certain critical densities various forces are overcome, turning the star into different states (e.g. white dwarf -> Neutron star -> Quark star...). Given the physics we know, stars of certain masses will inevitably collapse to blacks holes, so we don't need to construct the BH solution from scratch, we can actually see that real objects will evolve to that state given reasonable initial conditions.

The only way out is unknown physics, which is possible given the present problems with the theories.

Asymptotic flatness is merely a requirement enforced if you are looking at a vacuum solution. There is no reason that in a non-vaccum solution BH's can't form (i.e. a collapsing sphere in an FRW background) it just makes the maths a little more complicated, so textbook derivations often simplify things to a vacuum solution. The process of singularity formation has nothing to do with the conditions at infinity though, as you would expect since GR is a purely local theory.