I'm reading Wikipedia on Messier 87's jet
The relativistic jet of matter emerging from the core [...] consists of matter ejected from a supermassive black hole.
but later in the paragraph:
Its base [...] is probably powered by a prograde accretion disk around the spinning supermassive black hole.
Is the matter that is getting jetted away coming from inside of the black hole itself, or is it from matter that's just outside of the black hole?
All black holes have limits on the amount of angular momentum that they have and because they are very small compared with age size of any other objects of a similar mass the collapse to that size requires a lot of angular momentum that is in the cloud because of its turbulence to be shed.
The accretion disk is material orbiting the black hole is losing potential energy as it gets closer to the hole;e but gaining kinetic energy and interacting with the particles and getting hot in a process similar to star formation.
Consider now a reasonably dense accretion disk around any object with interacting particles. How can it loose this energy and angular momentum?
it can radiate electromagnetic radiation if it is a plasma but this does not cause much loss of angular momentum because photons are emitted in all directions and do not carry much momentum. the main way it can lose angular momentum is by particles colliding and getting thrown out.
They cannot be thrown out in the direction of the accretion disk because of the density of material causing rapid collisions there the only way out is perpendicular to the accretion disc and the closer to the photon sphere the particles get the more tightly focus the beam is to the axis of rotation also ether higher energy the particles and radiation has because they are orbiting at speeds close to the velocity of light. Hence the very high energy highly focussed jets coming from the station poles.
This process happens with any gravitational accretion process and can also be seen in areas of star formation although of course the violence and focus of the bipolar ejections of material is less than from a black hole. these bipolar mass ejections are indications of stars forming inside dense interstellar clouds even when the stars themselves are hidden by the dust clouds.
