Active galactic nucleus - Wikipedia
https://en.wikipedia.org/wiki/Active_galactic_nucleusBlack hole plasma jets are shaped like bell-bottoms | Science News
https://www.sciencenews.org/article/black-hole-plasma-jets-are-shaped-like-bell-bottomsCollimation, Acceleration, and Recollimation Shock in the Jet of Gamma-Ray Emitting Radio-loud Narrow-line Seyfert 1 Galaxy 1H0323+342 - IOPscience
https://iopscience.iop.org/article/10.3847/1538-4357/aac49fTHE STRUCTURE OF THE M87 JET: A TRANSITION FROM PARABOLIC TO CONICAL STREAMLINES - IOPscience
https://iopscience.iop.org/article/10.1088/2041-8205/745/2/L28