[at_a_remove]

I have been, rather annoyingly, been downvoted quite often in the past for being really clear on "dark matter," which is to say that astronomers study --broadly-- stars and their assemblages, things that emit light. Dark matter can encompass anything that doesn't shine like a star, be it exotic particles or just cold interstellar gas, little black holes, whatever. It isn't necessarily some Star Trek shit. It is just stuff we can tell exists by its gravitational signature on things that do shine -- light matter, aka stars.

[nisegami]

It's not just that it doesn't emit light, it doesn't appear to reflect or absorb light either. If it did, we should be able to pick it up through spectral analysis.