Their orbits suggest they have been gobbled up.
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I think they must be the cores of galaxies left after the host galaxy has stripped the outer stars... they may have been spirals but have now lost their arms..
I dont know if this is right but I think spiral galaxies travel thru space oriented like a pie being thrown in ones face.
.. so their direction of travel sees them meeting other galaxies the same way..the smaller galaxy passes thru and starts to orbit loosing its outer stars..
the orbit continues but only the core is left ..
and maybe as time passes the globular moves more to the orbit of the galactic plan where the core of the smaller galaxy is finally consumed..or rather its old structure disappears as its stars get scattered in the galactic plan of the host galaxy...why do they stay in a bunch.. gravity is acting upon them... how ....I dare not say.
So if old galaxies could it be that each hide a black hole??? is this where the galaxy gets its extra mass.. who knows what does a globular weight?
alex