Tom,
"the formation of gravitational black holes...involves no force." Do we know that? Is not the intrinsic rotation of matter in space to some virial radius a 'force'?
A Lagrangian point is a 'centre of mass' position where toroidal gravitational field potential cancels to zero (we have 5 in the Earth/Sun/Moon system). The centre of Earth is another. The main difference with an active galactic nucleus (AGN, or SMBH in old money) seems to be that the latter is in fluid motion. But vortices are 3D not the 2D modelled here. The tools do exist in 'Lagrangian Coherent Structures'
http://chaos.aip.org/resource/1/chaoeh/v20/i1/p017501_s1?bypassSSO=1">(LHC's Intro.)](https://
http://chaos.aip.org/resource/1/chaoeh/v20/i1/p017501_s1?bypassSSO=1) but are a bit complex.
I read this paper on arXiv and was concerned at some major bodies of research it had missed. In Eddies as in EM toroid acceleration (see Nuclear Tokamak experiments) the apparently chaotic flow 'self-organinses' into helical flow, with strong similarities to the patterns found in AGN accretion and jets. Also the 'stable boundary' ring assumed (including by Poe) is not so at all, it's highly dynamic. To explain;
If you watched the Americas Cup races you'll have noticed the 'tide lines', which are 'foam' propagated at the frame (flow direction) transition. Look closer and you'll have seen the larger of the small vortices along this line. At each vortex (eddy) there may well be a maintained ring of foam. However the assumption that this signifies some 'barrier' is wrong.;;
The foam is being continuously propagated by the shear 'plane' as the surface water rotates, accelerates and 'enters' the vortex (dye tests confirm this), whereon it's dragged around and down and eventually exits at the bottom (applause to John!). There's a vertical contra flow outside (common in Kansas). Did you never wonder where the air came from to 'lift' the cows? So the 'form' of the ring is maintained but it's constantly replenished. Watch the time line for a while and you can see it translate laterally across the bay.
The point then is not that the mathematical model for black holes is different, but that it's assumptions may be incorrect, so slightly different one may apply to both. Interestingly, the outflows from AGN's have been shown to actually contain more mass that accreted! (for which there are a number of possible explanations). In that case it may be said that black holes often appear to "eject more than they swallow." But that's astronomy not theoretical physics, which often seem to differ.
I hope that made a bit more sense than the paper. If anyone's interested in any particular aspect I have some links.
Best wishes
Peter