[Geminidog]

Would it be possible for all the missing matter to be just unseen baryonic matter? How are we sure that most of this is exotic dark matter?

[rossdavidh]

In the article, it specifically says that the matter she found is, in fact, unseen baryonic matter, and not dark matter. She found a method for detecting it even though it's cold and not emitting any EM waves.

[Geminidog]

It's also clear meaning light passes through this baryonic matter.

My question is, how do we know that the "dark matter" we assume to be littered all over the universe isn't just clear baryonic matter?

I know that we infer the existence of dark matter through gravity so how do we know that this dark matter isn't just "clear" baryonic matter?

Any astronomers care to share their expertise?