Question about black holes

[Celli]

If the black holes, by definition don't emit radiation, where does the emitted radiation to explain the luminosity of quasars? Can anyone explain me, please? I really don't understand it.

Thanks already.

PS: I'm sorry if I made any mistake in grammar. I'm still learning English. [?]

 

[nimbus]

That's right: so if you continue this line of thought, the emissions must come from outside of the event horizon. What could happen outside the event horizon, but still near the black holes, that would cause emissions? Matter is falling into the black hole, going from mundane speeds, to event horizon speeds and densities.

 

[CalliArcale]

To extend that a little further, this means that the only black holes we can detect by their radiation are ones which are actively "feeding". A quiescent black hole is undetectable except by its gravitational influence on other objects -- which means there are probably quite a lot more of them than we've identified.

 

[nimbus]

Which the ESO managed recently:
Official ESO press release webpage with a number of pics & videos,
including this one.
Youtube clip on the study:
[youtube]http://www.youtube.com/watch?v=0Hmv-6qLM8Y[/youtube]
arxiv.org paper
Observatory page for the study