[pingou]

Is it a natural thought? I'm not an expert but I thought it would just bigger and bigger.

For the dumping matter part, they talk in the article of the hawking radiation, I think the astrophysical jet wouldn't reduce the mass of a black hole but only slow its rotation, as the matter haven't reached the event horizon it would not be considered part of it. Again, I'm no expert, so you shouldn't trust me.