On 22/02/2017 20:03, wrote:
It's been a while since I've explored this topic. Years ago no one
had posited this model and I was told it was wrong. I thought I'd
check if anything has changed since.

No. It's still wrong. The BH influence is confined to the small region
nearest the centre of the galaxy where they are in mutual orbit out to a
modest multiple of their separation. Fireworks will ensue when/if they
spiral into each other but apart from that once you are some distance
from their barycentre the total mass of everything else is the main
influence on the forces that a distant star encounters.

I suppose there is an outside chance that at certain distances from the
galactic centre resonance effects might cause stars to avoid certain
regions or orbital periods but it would be very difficult to spot.

Has anyone posited the following model for creating a galactic bar?

Two galaxies merge. A pair of massive black holes (and stars)
become trapped in orbit at some kpc separation (the ends of the
bar).

A bar of stars forms between them, probably having orbits that
are co rotating and longitudinal. In a frame rotating with the
forming bar, it would appear the stars are moving essentially
along a line within the bar.

At some point enough stars are within the bar that the gravity of
the stars between the BH's causes the massive black holes to slide
down the bar to the center, where they orbit and merge.

We see the bar and we see a line of dust down each bar, that curves
into what appears to be a circular trajectory near the center.

See: https://en.wikipedia.org/wiki/Barred_spiral_galaxy

to see the dust lanes.

Any aspects matching (or refuting) this model been observed?

None that I can think of.

Moreover numerical simulations of the evolution spirals into barred
spiral galaxies tends to suggest that they are an inevitable consequence
of small pertubations of the whole ensemble as it tries to find a lowest
energy state after being shaken up by an interaction. eg.

https://arxiv.org/abs/1211.6754

[[Mod. note -- One big problem with this model is that massive black
holes aren't massive enough to dominate the stellar dynamics at kiloparsec
(= galactic-bar-size) distances. That is, on the size scale of a galactic
bar, even a "supermassive" black hole is still only a tiny fraction of
the mass in stars, interstellar gas/dust, and maybe dark matter.
-- jt]]

Indeed.

--
Regards,
Martin Brown