What is an accretion jet in black holes?
An accretion jet is an emission of high energy particles.
Black holes often acquire an accretion disk which is a disk of material falling into the black hole.
The supermassive black holes at the centres of galaxies often have enough material around them to form an accretion disk.
It is a common misconception that black holes eat everything which comes near them. In fact it takes a very long time for material to enter the black hole because time slows down the nearer something gets to it.
As more and more material falls into the accretion disk it gets heated by friction and gravitational effects. It can get so hot that it glows very brightly.
It is thought that the rotation of the accretion disk can cause magnetic fields which eject the particles from the disk at near light speed. These are the accretion jets.