# Center of a black hole.

#### 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.

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#### HallsofIvy

Homework Helper
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 cancelled 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

Gold Member
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

Gold Member
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

Gold Member
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

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#### 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

Gold Member
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.

#### stevebd1

Gold Member
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

Gold Member
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

Staff Emeritus
Gold Member
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

Gold Member
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.

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