Dark matter is currently understood to simply be matter that doesn't emit light; we don't know its composition for sure, but some suspect it's "normal matter." Alternatively, one paper I read said that the Dark Matter we're predicting is actually only due to statistical error if we abandon the notion that matter is distributed evenly throughout the universe.-Part of the beauty of the plasma model is that it doesn't require even distribution of matter, so it does not require untestable, unfalsifiable hypothesis.