Differential rotation of galaxies

what about the idea of a huge center object of a galaxie elliptical or not? Does a MM hold up on it?It sounds logical

The intuitive mind

The acceleration of the rotation near the center need a big mass in a small volume.
This suggest a big big black hole having the mass of millions suns. Other sugestions ?

Check I did and update on an earlier post. This link is a very interesting ***
[url] bustard.phys.nd.edu/PH308 [/url]

Back to rotation:
The gravity of the blackhole follow the Kepler inverse square because it is so small, so it will not have a big effect on the rotation off the arms. I saw some others models implying two elleptical each having a blackhole, collide and merge to give a spiral.
<img src=" www.polaris.net/~ksn/gal_evol.gif " border=0>
[url] www.polaris.net/~ksn/ [/url]
Good lecture!

We know that there are indeed some strange dense bodies towards the center of our galaxy producing tremendous energy. Conventional theory believes that the galaxy formed from a large rotating mass of gas. I have often wondered however if there was an original supermassive body that basically sputtered out stars in a series of disruptions. The galactic arms would then be like water spraying out from a lawn sprinkler. Where did this body come from? Perhaps as a seed from an even larger one that forms a whole galactic cluster.

Another explaination for the rotation velocity of galaxies is they are disks and have mass that is not at the gravity center. The disk structure cannot be modeled like you model a sphere with the assumption the mass is centered at the geometric center. Mass is not centered at the geometric center of a disk or a sphere, but in the case of a sphere it can be assumed for calculations that this is so-in a disk the assumption doesn't work. The mass is spread throughout the disk and alters the velocity.

I continue to explore sites that can give informations and theories about galaxies and the universe.

You can see nice glaxies photos and many more taken by the HST. One in particular of the region around a blackhole at the center off ???
[url] oposite.stsci.edu/pubinfo/SubjectT.html [/url]

You can also see edge on spirals and remark the dark dust lane. Is there an estimate of the mass of this dust?

Like you said Jim, the distribution of matter in a spiral galaxy is not spherical but more a disk distribution. If for a spherical symetric we need a density function of 1/r2 to get a constant velocity, then (I gess I am not mathematician) then to get a constant velocity in a disk symetric we need a density function of 1/r. Will this reduce the 'missing mass' ?

Like you see I have more question than aswers, but I am an astronomy passionnate and I try to understand the universe we live in. And I am happy to see that I am not the only one!

One one ever did the math right for a disk structure. I hope someone good at math will do this it would be a new way of exploring and may lead to better or improved models.