On 26/02/2017 04:43, wrote:
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).

Entropy doesn't mean what you think it means.

When a galaxy is formed the original conditions determine how much total
angular momentum it inherits from the gas cloud that it formed from. The
ratio of mass to angular momentum influences what it looks like and at a
certain amount of angular momentum spontaneous symmetry breaking occurs
and the whole thing looks much more complicated.

Q Is it known at what ratio of mass to angular momentum a forming galaxy
necessarily becomes a spiral rather than elliptical?

Here is one paper I found which tries to address the problem
semianalytically. I found another but lost the link. Perhaps someone can
suggest a better review of the morphology and secular of galaxies in
relation to their instrinsic angular momentum.

https://arxiv.org/pdf/1605.00647.pdf

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.

ISTR that in the early days of large scale galactic simulations they had
to work very hard to prevent bars from falling. I suspect bars and
ellipticals represent a galactic manifestation of Ovenden's conjecture
that stellar systems evolve towards configurations where the stars keep
their distance from each other as far is possible.

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?

Certainly small angular momentum.

And slowly getting smaller by expelling the odd star to infinity and the
remainder becoming ever more tightly gravitationally bound.

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.

That is because angular momentum scales as Mr^2

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

But that is the only thing that will work (or a galaxy with same spin
whose orbit is retrograde to the first and with goldilocks conditions to
null out the total angular momentum). Angular momentum is a *vector*
quantity you have to add an equal and opposite amount to null it out.

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

Nonsense. If you added an orthogonal amount of angular momentum to
original galaxy one with W1 = (I, 0, 0) and add W2 = (0, I, 0)

You get a new merged galaxy with WTot = (I, I, 0)

In other words sqrt(2).I and at 45 degrees to the original spin axis.

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.

You really do not understand the basics of Newtonian dynamics.

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.

Angular moment is one of the key invariants that is conserved in an
isolated system - and that remains true even in the full GR treatment.

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)

It doesn't work like that.

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

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

But the angular momentum would remain the *same* the galaxy might spin
more slowly as it became more massive since the same angular momentum
would be shared by a larger total mass

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

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

Sorry but you do not have a clue.

--
Regards,
Martin Brown