  We suggest that the dark matter model based on Bose Einstein condensate or
scalar field can resolve the apparently contradictory behaviors of dark matter
in the Abell 520 and the Bullet cluster. During a collision of two galaxies in
the cluster, if initial kinetic energy of the galaxies is large enough, two
dark matter halos pass each other in a soliton-like way as observed in the
Bullet cluster. If not, the halos merge due to the tiny repulsive interaction
among dark matter particles as observed in the Abell 520. This idea can also
explain the origin of the dark galaxy and the galaxy without dark matter.
