# Why a black hole sucks nearly everything, but emits gravitons?

What is so inherently different to the idea of gravitons from other particles, that a black hole draws everything possible including massless photons, but emits gravitons the more the stronger it grows?

If this is something obvious like "^%#^& magnets, how do they work?" please close the question but at least point me to the direction in which should I look.

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black holes can have electromagnetic charge, so you could say the same thing regarding photons. – lurscher Sep 7 '12 at 14:30
– ungerade Sep 7 '12 at 14:50
It may help to indicate where you came across that claim so we know better in what context to address your question. – Willie Wong Sep 7 '12 at 14:50
Didn't come acroos it anywhere, I was just wandering. After reading link by @ungerade I see I made a mistake assuming a force acting (gravity) must involve a particle (graviton). Looks like I have to explore the idea of fields, what a field means and how an excitation (particle) is different from the field itself. I thought field is like a potential to find a particle somewhere, and you actually need an observable particle to carry the force. – pafau k. Sep 7 '12 at 15:06

The photons and gravitons involved in static fields are not causal, they don't propagate along light cones. They are acausal things in a Feynman framework. Any gauge charge is visible outside the black hole, this is because gauge fields are determined by a Gauss law at infinity.

A good classical picture is that a charged black hole has a charge-per-unit-area on the horizon, which is considered as a GR version of an charged plate, the charge per unit area is the electric field density on the horizon, while the horizon always carries mass per unit area away from extremality, and this is by the surface gravity of the black hole.

These classical picture don't refer to particles, only to fields. The duality between particle and field description is subtle, and should not be used for casual arguments like this.

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