Quote:
Originally Posted by Jerry
The difference is, in the Bullet cluster, the Dark Matter appeared to avoid the collision: and in this case, Dark Matter appears to reside in the middle. You really cannot have it both ways; so something is not understood.
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You might be able to have it both ways. The Bullet cluster represents a recent collision, and Abell 520 represents two or more clusters that collided long ago. The luminous matter in the Bullet cluster is still bound to one or the other of the dark matter clouds, and will in the long run redistribute itself as galaxies with too much orbital energy to ever approach the center again.