Nobody really knows the exact mechanism that forms the beams, but the beams definitely do not shoot out of the black hole. Of course that’s usually what you see

Nobody really knows the exact mechanism that forms the beams, but the beams definitely do not shoot out of the black hole. Of course that’s usually what you see in an artist’s depiction of them, but that’s a whole different problem. The beams come from the accretion disk. There are two opposing beams because the disk has two opposing faces. The profile of the disk is narrow, so it stands to reason that very little radiation would leak out around the edge. On the other hand, there is a black hole in the middle of the disk and that should be smearing the beam out quite a lot. Somehow the magnetic fields and currents within the disk must conspire to keep the beam fairly narrow.