2024ApJ...962...18L

We point out the dominant importance of plasma injection effects of relativistic winds from pulsars and black holes. We demonstrate that outside the light cylinder, the magnetically dominated outflows sliding along the helical magnetic field move nearly radially with very large Lorentz factors, γ₀ ≫ 1, imprinted into the flow during pair production within the gaps. Only at larger distances, r ≥ γ₀(c/Ω), does MHD acceleration Γ ∝ r take over. As a result, Blandford-Znajek (BZ)-driven outflows produce spine-brightened images. The best-resolved case of the jet in M87 shows both edge-brightened features, as well as weaker spine-brightened features. Only the spine-brightened component can be BZ driven/originate from the black hole's magnetosphere.