3 Answers

There is also black matter besides black energy, but they have not been found yet, it's still only a theory. Perhaps it's time for those galaxies to end. All things come to an end some time or other.

The dark matter could be carbon. Such material would be black and reflect nothing. Since it is light weight it would be fast in responding to gravitational and electrostatic variations over vast expanses. Carbon readily bonds with many chemical gasses this would explain the observed variations reported in differing regions of space. The analysis of space gases and particle  are open to analysis  by several techniques that are reliable and have been used for years. Radio frequency analysis in combination whit optical data has provided inside into these issues. 

The second part of your question deals with Galaxy collisions . http://cas.sdss.org/dr3/en/proj/basic/galaxies/collisions.asp   

this site can help in the question.

Thanks to robergrist, for the sight on galaxies.  Interesting.  The TV broadcast stated the dark matter was necessary for development of those subjects we see in space.  The lack of dark matter was said to be the lack of a force (gravity) to form galaxies, etc.  Without dark matter, we would not be here (as reported).  I can only presume that these are recent findings since I have heard of them until now.