How Do Gravitons Leave Black Holes?

[Rev. Green]

How does a black hole attract matter if nothing, except a small amount of Hawking radiation, can escape?

[Old_Geezer]

But your whirlpool is using the Earth's gravity !

https://media.ao.com/en-GB/Productimages/Images/rvLarge/fwg71484w_wh_whirlpool_washer_1a_l.jpg

[beso]

Anything to do with Black Holes can only be described by Physics outside of the Event Horizon because the laws of physics do not apply "inside" a Black Hole. If gravitons do exist then they would only be describable from the Horizon outwards.

Same as Hawking Radiation which occurs at the Horizon where one of a pair of virtual particles is created inside and the other outside. We can't describe what goes on inside.

If Gravitons exist they would probably not have a mass. They mediate the gravitational field rather then being affected by it. As such they wouldn't have a problem leaving a Black Hole anyway.

By analogy, photons mediate electromagnetic fields rather than being affected by them.

[Rev. Green]

Yes, I agree with Old Geezer, they come from just outside the event horizon. In our time frame, black holes don't exist, yet! - because our time is infinitely dilated near them. But it appears to me that the gravitons (if any) from the matter which is forming the black hole will become more and more red-shifted (and weaker?) as the matter nears the event horizon.

[Rev. Green]

Beso, photons and gravitons have no mass, but they do have energy, so they are affected by gravity.

[ToraToraTora]

crikey, I think we'd better leave spath to handle this one!

[jim360]

OG's answer was what I had in mind myself, although even that's still not necessarily right.

Gravitons (if they exist) are excitations of the gravitational field, so in fact they needn't be emitted from the black hole at all. Instead, it would be a local interaction at the point of spacetime where the matter is, and *that* is where the graviton would be "emitted".

I don't know how clear that answer is, but in any case, whether it's OG's answer or mine, the net effect is the same: gravitons never need to escape from the black hole.

A couple of side points:

1. Beso says that "If Gravitons exist they would probably not have a mass. They mediate the gravitational field rather then being affected by it... By analogy, photons mediate electromagnetic fields rather than being affected by them."

This analogy, however, doesn't quite work. Photons aren't affected by EM fields, it is true; gravitons are also analogous to photons. But there is a difference. Photons cannot interact with other photons (at least, not directly), whereas gravitons *can* interact directly with other gravitons.

The more correct analogy would therefore be with a "gluon", which is the equivalent of a photon for the Strong Force. These can interact with each other, in the sense that gluons also feel the strong force, rather than just carrying it.

2. As Rev. Green points out, gravitons have energy and are therefore affected by gravity -- this is why photons can't escape from black holes either. Both gravitons and photons would, in pure form, follow the shortest possible path between any two points. That path changes depending on the strength of gravity in the area. The difference between gravity acting on massive objects (eg other stars) is the shape of this line, but in either case, as long as there is gravity present, then the line is certainly not "straight".

[ToraToraTora]

3. we know that bosons can have mass, eg the mass boson, the higgs, is around 126 gev.

[Rev. Green]

I've found the answer on the web: photons and gravitons escape freely from a black hole as virtual particles which, as they can travel at any speed between zero and infinity, can travel faster than light. The information about the charge or the mass of the black hole is, of course, limited to travelling at the speed of light.

[douglas9401]

I had hoped the answer would be something as simple as 'they use the gravi train'.

[jim360]

I had also found that answer, Rev. Green, but one needs to be careful! Virtual particles are not real (hence the name), so any explanation in terms of "virtual particles" *always* has a more physical explanation instead.

This is why, instead, I gave the following answer:

// Gravitons (if they exist) are excitations of the gravitational field, so in fact they needn't be emitted from the black hole at all. //

This is essentially the same idea as the answer you found, but is more physically reasonable.