Abstract
There is a general consensus that magnetic fields, accretion disks, and rotating black holes are instrumental in the generation of the most powerful sources of energy in the known universe. Nonetheless, because magnetized accretion onto rotating black holes involves both the complications of nonlinear magnetohydrodynamics that currently cannot fully be treated numerically, and uncertainties about the origin of magnetic fields that at present are part of the input, the space of possible solutions remains less constrained. Consequently, the literature still bears witness to the proliferation of rather different black hole engine models. But the accumulated wealth of observational data is now sufficient to meaningfully distinguish between them. It is in this light that this critical paper compares the recent retrograde framework with standard “spin paradigm” prograde models.
Highlights
When Roy Kerr presented his solution at the Texas Symposium almost five decades ago, the astronomical community, ironically, was too busy with the recent discovery of quasars to pay attention
Despite a common foundation grounded in accretion and black hole spin, the gap paradigm and spin and hybrid spin paradigms (SHSPs) differ in substantial ways
(2) In the gap paradigm, FRII quasars evolve into FRII radio galaxies or FRI quasars and eventually either into FRI radio galaxies or radio-quiet quasars; while in SHSPs, FRII quasar evolution has no clear or model-constrained scaleinvariant progression
Summary
When Roy Kerr presented his solution at the Texas Symposium almost five decades ago, the astronomical community, ironically, was too busy with the recent discovery of quasars to pay attention. Hybrid spin paradigms explore the ramifications of high/low black hole spin surrounded by thin- disk or advection-dominated accretion in an attempt to enhance the jet efficiency These ideas have been in part a response to arguments against powerful jets in black hole systems due to diffusive effects [30,31,32], suggesting that the black hole-threading magnetic field would be too weak for the BZ mechanism to explain the observations. While the most radical departure from the spin paradigm, referred to as the “gap paradigm” [37], is constructed from the basic building blocks of the other models (including BZ, BP, and thin/thick disks), it and crucially, hinges on the ability of retrograde accretion to produce the most powerful jets This framework, argues that in addition to high/low black hole spin and thin-disk/advection dominated accretion, retrograde/prograde directions between disk and black hole matter. Because the track record on the discussion of compatibility between theory and observation has been poor, that is the focus of this paper
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