Quote:
Originally Posted by strongmanmike
Well it looks to me Robbo like something was doing burnouts and doughnuts around this galaxy and has whipped the arms into threads...perhaps the little companion galaxy is the culprit? 
Mike |
Sounds like the revhead theory of spiral arm formation!
This is a
very strange galaxy, in its way, as the question can be asked "why aren't there
bright spiral arms in its outer regions, like there are in other spiral galaxies?" Why no bright arms? Perhaps there will be some bright arms, sometime in the future?
Take a look at the following image, which overlays the gas distribution in the outer region of this galaxy with the thin & knotty spiral arms that are seen both in your image and in the GALEX image.
(the cold gas, invisible to the eye, is displayed as green, and the Galex ultraviolet image is displayed as blue)
As you can see, the HI gas (the cold atomic hydrogen gas) forms a sort of "super-sized" spiral that
surrounds the visually bright part of this galaxy (the
bright part of this galaxy is composed of the ring that surrounds the bar, plus the bar that is inside the ring.).
The interstellar gas in this galaxy extends to many times the radius of the prominent and bright ring structure, which shows that this galaxy extends a long way further out than we think it does.
However, the distribution of
stars (as traced by visible light) seems to be very concentrated and bright only till we reach the outside edge of the bright ring structure..... and then the
surface brightness suddenly drops drastically outside of this ring structure.
So we have here a galaxy which has
formed plenty of stars in its inner part, up to the radius of the bright ring,
but which has formed hardly any stars outside of this ring.
(well, there do exist the thin arms outside of the bright ring, but this is hardly a grand and bright spiral structure)
Given that the gas in this galaxy is distributed in a spiral, and that the thin and knotty outer spiral arms seem to be forming in the places where this spiralling gas is the most dense, it would seem that the cause of the thin knotty arms in the outermost regions
must be connected with the spiral-like structure that is seen in the underlying gas
( you can't form the stars in spiral arms without having dense gas existing there in the first place, as a raw material for the star formation process.)
There is definitely "plenty of this galaxy existing outside of the bright optical part that is defined by the ring", but most of it is just interstellar gas that is distributed in this very extended spiral pattern.
Perhaps one day, the big gaseous spiral that is outside of the obvious part of this galaxy will form enough stars to make some really bright spiral arms!
My personal view is that this galaxy just
needs some more time to evolve, and that the outer gas spiral may one day turn into the bright spiral structure that we are used to seeing in other galaxies.......
Youd be getting close to Imaging time being less than processing time eh Mike 
