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Blandford-Znajek process without plasma

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In 1977, Blandford and Znajek  discovered a process by which a spinning 

black hole can transfer rotational energy to a force-free plasma, offering a possible mechanism for energy and jet emissions from quasars and other astrophysical sources.  This Blandford-Znajek (BZ) mechanism is a Penrose process, which exploits the presence of an ergosphere supporting negative energy states, and it involves currents of electrical charge sourcing the toroidal  magnetic field component of the emitted Poynting flux.  

In this talk, I will discuss a version of the BZ process requiring only vacuum electromagnetic fields outside the black hole.  The setting is somewhat artificial, since it assumes the black hole is cylindrical rather than spheroidal, or that the black hole lives in 2 spatial dimensions, but it is nevertheless of theoretical interest.  The radiation power and horizon regularity relations are identical to those of the BZ mechanism with plasma, and the solution can be given in simple, closed form for a wide class of metrics, so it helps to illuminate the nature of the original mechanism.  For asymptotically Anti-de Sitter black holes it presumably has an interesting dual CFT description, but we haven't quite yet figured out  what that is.