Clusters at center and periphery

[nomadreid]

An acquaintance has told me that the Sloan Digital Sky Survey found clusters of galaxies in which most of the galaxies were divided between the center and the periphery, with a smaller density of galaxies in between. Is this case, and if so, why?

 

[berkeman]

the center and the periphery

The center and periphery of what?

 

[nomadreid]

The center and periphery of what?

of the cluster