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In the Blandford-Znajek Process (which is considered a potential mechanism to explain jets from AGN), the lorentz force is assumed to be vanishing (the force-free condition).

But we see that the lorentz factor for the outflow is quite high.

If there is no exchange of energy from the electromagnetic fields to the charged particles, how are these two facts reconciled?

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  • $\begingroup$ Can you provide a reference for your two facts? $\endgroup$
    – ProfRob
    Commented Jun 4, 2023 at 11:40
  • $\begingroup$ High Lorentz factor: "The fastest AGN jets are gamma-ray bright, with flow Lorentz factors that range up to at least 45" bu.edu/blazars/paperstodownload/marscher_michiganjets.pdf No exchange of energy: " Forcefree electrodynamics (FFE) describes the electromagnetic field interacting with a plasma in a regime in which the transfer of energy and momentum from the field to the plasma can be neglected" arxiv.org/pdf/1401.6159.pdf $\endgroup$
    – jay121
    Commented Jun 7, 2023 at 15:06
  • $\begingroup$ The term "force-free" in the Blandford-Znajek process refers to the Lorentz force's minimal impact on charged particles as a result of the strong coupling of the electric and magnetic fields surrounding the black hole. The high Lorentz factor, on the other hand, refers to the relativistic velocity of plasma particles. They are two different ideas. It is the intricate interaction between the revolving black hole, magnetic fields, and the accretion disk—not forces on particular particles—that drives the acceleration of plasma to relativistic speeds and the extraction of energy in the BZ process. $\endgroup$
    – Caetes
    Commented Jun 9, 2023 at 13:58

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