On Thursday, February 23, 2017 at 7:47:09 AM UTC-8, Martin Brown
The general theory is that as galaxies age they mature towards having a
barred spiral structure through perturbations of the stellar orbits in
the galactic gravitational potential. See for example:

https://www.nasa.gov/mission_pages/h..._galaxies.html
http://hubblesite.org/hubble_discove..._evolution.pdf

The same happens in numerical simulations of stars in galaxies.

Nice images, some of my favorite galaxies.

The sequence for bar evolution seems backwards to me (counter to
entropy which wants to randomize things....globular clusters and
ellipticals seem to me to be the end stage of evolution).

The formation of a bar also seems counter to Rubin observation that
the circular velocity is constant with radius.......the larger
circular orbit would inevitably sweep the arms into a spiral.

This is more the sequence that I'm studying / seeking evidence for:



1) Mice https://en.wikipedia.org/wiki/Mice_G...Telescope).jpg

2) Fornax https://en.wikipedia.org/wiki/Barred...a-99-hires.jpg


3) ngc1097 https://en.wikipedia.org/wiki/NGC_1097

4) ngc1232 https://en.wikipedia.org/wiki/NGC_12...e:NGC1232B.jpg

This is about opposite the sequence at the Hubblesite link you sent.

Basics:

The net angular momentum of a globular cluster of stars is zero,
right?

Same for an elliptical (generally and ignoring the possible small
rotation component some have).

In contrast, spirals have large angular momentum in their outer
disk stars, vs (much? near zero) smaller angular momentum in their
central bulges of stars.

As suggested, To merge a counter rotating galaxy is a way to zero
out the angular momentum. That's not what I'm suggesting.

If you instead add angular momentum that is orthogonal, then you
randomize the stellar orbits. This is what we see in ellipticals
and globulars.

The angular momentum of matter raining down along an approximately
axial line (ie, in a highly elliptical orbital geometry, with the
long axis of the ellipse being the rotation axis of the galaxy.
Then, the axis of rotation for the galaxy is orthogonal to the axis
of rotation for the ellipse of in falling material.

As this "rain" component becomes "thermalized" by interacting with
the mass of the galaxy, some of the disk stars orbits are transformed
into elliptical orbits. In this way, a spiral galaxy could evolve
to become an elliptical galaxy.

And it all began from the BH that ejected matter along the axis of
too much angular momentum. Each episode of activity, increasing
the size of the bulge, until eventually the galaxy is an elliptical
and the stars can age from there............(ellipticals have older
stars)

I'm not talking (primarily) about BH angular momentum here, I'm
talking about galactic angular momentum.

BUT, over time, whatever angular momentum the galaxy has winds up
being communicated throughout the system and right into the center
where it then tells the BH what angular momentum it must adopt
because it's angular momentum results from the stuff falling into
it, and not the other way round..............

In this model, an active BH happens when an excess of angular
momentum is communicated into the BH environment. It ejects material,
the material rains down, interacts and randomizes angular momentum
of the galaxy, the BH goes dormant and the spiral nature evolves
toward elliptical.



You would have to drop serious amounts of matter in a retrograde
orbit

Serious amounts of matter............yes

retrograde orbit.............no.

It needs to cancel out or randomize, the existing angular momentum.
See above.


rt