The shape of a black hole

Originally posted by Palynka
My whole knowledge of physics is basically pop-science, but I'm willing to learn! 🙂

To clear my mind:
1. Why would CERN's black holes collapse if not because of Hawking radiation?

2. So you're saying that the disks are matter and the jets are radiation, correct? But wouldn't the radiation (which the jets are made off) still be going away from the black hole?

1 - The existence of CERN's black holes isn't without controversy too. I personally think that they don't exist almost for certain.
From what I've read it was basically a few cranks and nuclear physicist that said that there was a real danger of black holes appearing, but I think that their main motivation was getting some publicity.
If you ask me the main factor for not fearing those hypothetical black is their really tiny event horizon.

2- The disk may possibly be a a mix of matter and radiation, but what causes the jets is the spiraling of matter into the black holes. Yes in principle the jets are moving away from the black hole, but I never said anything in contrary to that.

Originally posted by adam warlock
1 - The existence of CERN's black holes isn't without controversy too. I personally think that they don't exist almost for certain.
From what I've read it was basically a few cranks and nuclear physicist that said that there was a real danger of black holes appearing, but I think that their main motivation was getting some publicity.
If you ask me th ...[text shortened]... the jets are moving away from the black hole, but I never said anything in contrary to that.

Right, so it's likely that they won't even appear. check.

If they do but the on't collapse, why would a tiny event horizon matter? The gravitational pull of the black hole is not restricted to the event horizon, right? I thought that IF black holes appear, they MUST almost immediately collapse or else we're...you know.

Originally posted by Palynka
Right, so it's likely that they won't even appear. check.

If they do but the on't collapse, why would a tiny event horizon matter? The gravitational pull of the black hole is not restricted to the event horizon, right? I thought that IF black holes appear, they MUST almost immediately collapse or else we're...you know.

The gravitational pull of the black hole is not restricted to the event horizon, right?
The gravitational pull extends through all space but the no turning back points are at the region given by the event horizon.

Originally posted by adam warlock
The gravitational pull of the black hole is not restricted to the event horizon, right?
The gravitational pull extends through all space but the no turning back points are at the region given by the event horizon.

So wouldn't then the gravitational pull be a problem if the BH doesn't collapse almost instantly?

Originally posted by Palynka
So wouldn't then the gravitational pull be a problem if the BH doesn't collapse almost instantly?

No, because the mass of the nano BH is way too small to have any real effect in macroscopic bodies.

As an example just picture this: you're standing 1 cm for an orange. Do you feel any gravitational pull towards the orange? No, you don't. The nano BHs have masses way smaller than an orange so you won't feel a thing for sure.


I'm too lazy to look it up but if you provide me with the masses of the hypothetical nano BHs I can do some calculations for you.

Originally posted by adam warlock
No, because the mass of the nano BH is way too small to have any real effect in macroscopic bodies.

As an example just picture this: you're standing 1 cm for an orange. Do you feel any gravitational pull towards the orange? No, you don't. The nano BHs have masses way smaller than an orange so you won't feel a thing for sure.


I'm too lazy to loo ...[text shortened]... provide me with the masses of the hypothetical nano BHs I can do some calculations for you.

Don't sweat it, that's a fine answer to what I was looking for.

Originally posted by Palynka
Don't sweat it, that's a fine answer to what I was looking for.

In that case give your mass and I'll look up the BHs mass and do some nifty calculations.

Originally posted by adam warlock
In that case give your mass and I'll look up the BHs mass and do some nifty calculations.

For my mass you'll have to wait until Sunday.

Originally posted by Palynka
For my mass you'll have to wait until Sunday.

Why, are you eating an especially large meal?

It seems to me we will know nothing about black holes till a quantum theory of gravity, or some kind of string theory breakthrough. Ordinary physics breaks down inside a black hole. They talk about infinite density which is just plain silly. There are new theories, not verified as of yet that propose 'space atoms', the fundamental 'particle' of this brand of physics. If you want I can get a link. The author and I emailed a couple of times so you could too.

Originally posted by adam warlock
It has been proven for some time that under gravitational collapse a black hole is always spheric in shape.

Just checked some notes. This happens in time for rotating black holes. It isn't immediate but it always happen after a period of time.

Are we talking about the shape of the event horizon? Do you have any references as I cant seem to find any.

Originally posted by adam warlock
I think that it was Roger Penrose who proved that under gravitational collapse a black hole always achive a spherical form.

I try again:

If the black hole is rotating it's perhaps flattened a little, I don't think you can see the flattening though.

Under perfect condition it is spherical, those conditions doesn't involve rotational black holes.

Originally posted by twhitehead
Are we talking about the shape of the event horizon? Do you have any references as I cant seem to find any.

Yes, I'm referring to the event horizon topology. I had to go really deep and after all it appears that the theorem is due to Hawking (but I ay be confusing with this http://en.wikipedia.org/wiki/Penrose_process). It proves that all stationary BH in 4D space-time have a 2-sphere topology. Rotating black holes are oblate, but since the rotating black hole emits energy we know that in time it will just turn into a 4d stationary BH which has a spherical event horizon.

http://en.wikipedia.org/wiki/Rotating_black_hole#Conversion_to_a_Schwarzschild_black_hole

Ps: And here is a nice introduction to GR to people who want to get a feel of it: http://preposterousuniverse.com/grnotes/grtinypdf.pdf

Originally posted by adam warlock
Rotating black holes are oblate, but since the rotating black hole emits energy we know that in time it will just turn into a 4d stationary BH which has a spherical event horizon.

Surely the earth too is slowing down and will eventually stop rotating, but is that a reason to declare that all planets do not rotate?
It was my understanding that all black holes would have some rotation and that to a large extent that angular momentum would be conserved for a very very long time.
I also see no reason why two singularities cannot orbit one another (as binary stars do) and thus have a more exotic shaped event horizon.

Originally posted by twhitehead
Surely the earth too is slowing down and will eventually stop rotating, but is that a reason to declare that all planets do not rotate?
It was my understanding that all black holes would have some rotation and that to a large extent that angular momentum would be conserved for a very very long time.
I also see no reason why two singularities cannot orbit one another (as binary stars do) and thus have a more exotic shaped event horizon.

"Surely the earth too is slowing down and will eventually stop rotating, but is that a reason to declare that all planets do not rotate?"
No it isn't. But the fact that all BHs radiate energy is a reason to say that eventually they will stop rotating.

"It was my understanding that all black holes would have some rotation and that to a large extent that angular momentum would be conserved for a very very long time."
I'm not saying that the eventual stop will happen tomorrow I'm just saying it'll happen.

"I also see no reason why two singularities cannot orbit one another (as binary stars do) and thus have a more exotic shaped event horizon."
From what I know of GR a BH can only have a single singularity. If you look at the equations you can easily see why. Maybe with some stranger mathematics things can get a little weirder, but I think that present day knowledge your scenario is impossible.

Originally posted by adam warlock
No it isn't.

Actually it is due to the tidal effects of the moon. Obviously though it can only slow down to the period of the moons orbit.

But the fact that all BHs radiate energy is a reason to say that eventually they will stop rotating.
But who cares if that is billions of years in the future?

I'm not saying that the eventual stop will happen tomorrow I'm just saying it'll happen.
So how is it relevant to the shape of those black holes today?

From what I know of GR a BH can only have a single singularity. If you look at the equations you can easily see why. Maybe with some stranger mathematics things can get a little weirder, but I think that present day knowledge your scenario is impossible.
I am afraid I am not familiar with the equations, but it seems pretty obvious that your conclusion is not valid. Surely the laws of physics hold just as much inside the event horizon as they do outside it? I thought it was only at the singularity that they had issues. Even if I am wrong, if two black holes are orbiting each other, event horizons and all (that certainly is possible), and the event horizons touch, they surely won't instantaneously combine into one singularity - therefore the equations cant possibly rule out my scenario.