Brainstorming: Incorporate Dark Matter in a campaign

[Anders]

So I learned on Twitter that they've found a galaxy made up almost entirely of dark matter. That made me think about dark matter and how to incorporate it into a gaming world. Presumably IN SPACE, although I could easily see it in a horror campaign as well.

So what would you do with Dark Matter in a campaign setting? I'm thinking of having it as a kind of "dimensional shadow" of a parallel universe. We can see the gravity here, but no other forms of radiation. And somewhere there is a portal... and something wants to open it.