posted on Jan, 24 2004 @ 05:30 AM
There are several candidates for the dark matter in the universe. You can split them in two groups: those from normal matter and those from exotic
The normal matter candidates are made from normal matter, don't send out light. Among these candidates are planets, the remain of died stars (brown
dwarfs, white dwarfs, black holes) and just your normal stone floating around. These structures can't explain all the dark matter, because there
wasn't enough matter formed if our theories on the big bang are right.
Therefore scientists started looking into exotic matter. The first candidate are neutrino's. These particles are very difficult to detect, but have
been proven. We know that if they have mass, they have very little mass. This is not really problem, since there so much neutrino's. A mass of 1/5000
of the electron mass would mean enough dark matter.
Some scientists have also offered stranger kinds of matter as a possibility for dark matter. They are called WIMPs (Weakly Interacting Massive
Particles). These are all not proven to exist. Examples include neutralino's, axions and magnetic monopoles.
So, yes, there can be dark matter galaxies. These will be made up from planets and the remains of died stars though. Those galaxies would probably
fall apart over time, because stars eject a lot of their mass when they die. Neutrino's and WIMPs don't interact a lot. They can't form structures
(with other particles) as protons or neutrons. Therefore they can't form stars and galaxies.