Galaxy with a "halo"

http://legacysurvey.org/viewer?ra=172.9769&dec=2.6405&zoom=15&layer=decals-dr5

Hi StarGazer, I noticed you posting a lot of these, and I think you should investigate the shapes of lenticular galaxies. This is a sort of intermediate area between spirals and ellipticals. In this case, the arms have seemingly wrapped around the galaxy, merged, and become a continuous ring. Oftentimes the bar is still evident, as with this one. Other times, only a disk is visible, as with the famous Sombrero Galaxy.

Thanks Geckzilla. I am a total novice with regard to galaxy morphology, but I thought it worth highlighting some of the less usual types I see in case they are of interest to someone who is actually studying these things. Is there an “idiot’s guide” somewhere explaining the evolution of galaxies? I’d like to know why some galaxies have just two simple spiral arms while others have lots, and why some are just amorphous blobs!

The best “idiot’s guide” I can think of is really just the standard Hubble sequence along with the tuning fork, which shows generally how spirals evolve toward ellipticals:

Taxonomy is always fraught by intermediates, and a lot of things do not fit neatly into the tuning fork diagram either because they are chaotic, interacting systems or small, irregular galaxies. Remember that galaxies do not exist alone, but are all connected by a kind of cosmic web of gas. I think of galaxies as being places where this gas has formed into denser eddies, shocks, and knots where stars are more readily formed, and heavier elements exist.

Another thing that I found very useful myself was to take some online introductory astronomy courses. They are free and often also avoid difficult physics equations, although if you are mathematically inclined there are also some more math heavy offerings.

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Hi Geckzilla

Thanks for the link. I’ve seen the Hubble sequence for classification before, but I am more interested in the process of evolution of these structures. Hubble was at pains to point out that his classification was NOT an evolutionary path, just a diagram of different types of galaxy he had observed. (I was hoping new computer simulations might have been done to possibly shed light on how these different structures form and develop).

Hi Geckzilla

I thought this galaxy was notable because the “halo” is not the same shape as the central portion of the galaxy.

This is what I regard as a more typical lenticular galaxy, where the outer ring is clearly formed within the plane of the galactic disk, so has the same perspective as the central portion: RA,Dec = 178.3150, 60.6644

It has been used for a while to discuss not just classification, but also evolution, despite whatever pains Hubble took. I haven’t personally encountered anyone specializing in this sort of morphology specifically, though it has been my experience that lenticular galaxies are every bit as diverse as the spirals they are thought to evolve from. Well, best of luck with your quest, anyway.