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[Mgoblue201]

Two things I don't get:

1- How cam radiation can leave the blackhole? Wouldn't it be attracted back into it too?

2- Why is it that the giant mega star (I forget the name, but it's so huge it makes our sun look microscopic) can be so massive and yet not collapsed into a blackhole? You need even more mass than that?

I can (hopefully) answer that first question. The idea is that when a virtual particle appears close to the "event horizon" (or whatever replaces it in Hawking's model), that particle will become a real one. This will appear as a particle/antiparticle pair: one particle may escape to the outside world (because it's beyond the event horizon) and one particle may fall in. However, according to Sean Carroll, the total energy of a virtual particle/antiparticle pair is exactly zero. For the real particle, the energy can never be negative. So "if the real particle that escapes the black hole has positive energy, and the total energy of the original virtual particle pair was zero, that means the partner that fell into the black hole must have a negative energy. When it falls in, the total mass of the black hole goes down. Eventually, unless extra energy is added from other sources, a black hole will evaporate away entirely." So if you wait a sufficient length of time, particles can escape the black hole as it radiates away.

 

[Ether_Snake]

I learned today about radiation pressure. Basically as long as there is fusion, gravity is opposed to this pressure and the star is kept stable. Once fusion can't be done anymore because of lack of hydrogen to use, the star collapses and make other objects, potentially a black hole. So supposedly you don't need that much mass, but it needs to be inert.

I see. So it points back to this idea I spoke of in a thread before (for which I got bashed as always).

I said that no motion = no existence, and that if anything in the universe was to stop moving, it would "break" whatever is in contact with it since that would be interacting with something that has no force. For a force to exist, it can only exist in relation to another force exercized against it. Without interaction, nothing can be defined.

So when you have massive amount of mass, inertia is reduced, unless for example another force is contributing to inertia (such as fusion as you said, or something else). So without such a force, the more mass you have the less the particles are able to move, the equivalent of freezing them or adding pressure, to the point where eventually they become so stable they stop moving completely, and as such they lose their definition. Basically, the more mass and the less inertia, the closer you get to a point where particles stop moving, and when that happens the universe pretty much divides by 0 (0 being no energy, no motion; no information), so it just goes pop and things fall out of the universe.

I can (hopefully) answer that first question. The idea is that when a virtual particle appears close to the "event horizon" (or whatever replaces it in Hawking's model), that particle will become a real one. This will appear as a particle/antiparticle pair: one particle may escape to the outside world (because it's beyond the event horizon) and one particle may fall in. However, according to Sean Carroll, the total energy of a virtual particle/antiparticle pair is exactly zero. For the real particle, the energy can never be negative. So "if the real particle that escapes the black hole has positive energy, and the total energy of the original virtual particle pair was zero, that means the partner that fell into the black hole must have a negative energy. When it falls in, the total mass of the black hole goes down. Eventually, unless extra energy is added from other sources, a black hole will evaporate away entirely." So if you wait a sufficient length of time, particles can escape the black hole as it radiates away.

/headscratch

I have to reread this a few times

 

[Wray]

All those informations up there about what would happen if we fell in a black hole's event horizon are interesting, but not satisfying.

If I understand correctly, after we cross an event horizon all directions point to the singularity. But logic tells me that if it's the case, all movements beyond that point are impossible, should it be brain activity or blood flow.

So basically everything passing through an event horizon would just be frozen until spaghettification happens, and thus not compatible with any form of life. It would also mean that the insane gravity would probably kill us long before we even reach the event horizon, even in the case of a super massive black hole, as our blood flow would have stopped since it would be too weak to defy gravity.

So if I understand things correctly, event horizon or not, it doesn't really matter. No one would make it near a black hole alive.

Spaghettification would happen long before you got close to the Event Horizon.

 

[Wray]

2- Why is it that the giant mega star (I forget the name, but it's so huge it makes our sun look microscopic) can be so massive and yet not collapsed into a blackhole? You need even more mass than that?

The Star you are thinking of is Canis Majoris.

http://en.wikipedia.org/wiki/VY_Canis_Majoris

The reason why it hasn't turned into a Black Hole yet is because it hasn't collapsed yet. It's a pretty young star (All stars that size are). Once it exhausts its energy, it'll likely Hypernova and make a new black hole.

 

[Jinroh]

Spaghettification would happen long before you got close to the Event Horizon.

Apparently that's not the case with a supermassive blackhole.

 

[Mengy]

This is a fascinating thread. I saw episode 3 of the new Cosmos last night, the one where Neil goes into the event horizon of a black hole, but now after reading of Hawking's new theory he might just make that episode outdated already, lol.

Black holes are fascinating. But then most of the universe is.