Can a Galaxy Collapse Inward Over Time?

[wonderingx]

Is it possible for a galaxy too fall back into its self?(even if they don't) What would happen?

 

[LURCH]

I suppose gallaxies can all be thought of as falling into themselves. Theoretically, matter in the early universe was spread out much more evenly than it is today. Bits of matter that used to be individual stocks of dust and clubs of gas have come together into stars and other large bodies. Gravitational attraction has pulled these bodies of matter together in groups such as super clusters, clusters, and individual galaxies. On local scales (certainly on the scale of galaxies), the influence of the Hubble expansion is pretty much negligible compared with the influence of gravitational attraction pulling things together. So, the same force that caused the galaxy to "clump together" into a galaxy in first place is still pulling that galaxy ever tighter together.

At the center of most (if not all) galaxies a supermassive black hole is thought to exist. Throughout the life of the galaxy, more and more matter falls into this black hole. If the whole galaxy were to fall into the center, it would become nothing but one gigantic black hole.

 

[hellfire]

So, the same force that caused the galaxy to "clump together" into a galaxy in first place is still pulling that galaxy ever tighter together.

Are you sure about that? In http://math.ucr.edu/home/baez/end.html I read:

And you can show in the really long run, any isolated system consisting of sufficiently many point particles interacting gravitationally - even an apparently "gravitationally bound" system - will "boil off" as individual particles randomly happen to acquire enough kinetic energy to reach escape velocity.

 

[SpaceTiger]

My impression is that the answer is still very much unknown for sizable galaxies. I don't think anyone has run their models far enough in time (nor do they have enough faith in them) to predict the final fate of, for example, the Milky Way. In globular clusters, it seems that both of these things happen; that is, stars "boil off" with time, but the core of the cluster also contracts. It may be that something similar will happen to galaxies in the long term, but I suspect our models are not yet sophisticated enough to say for sure.