Could neutrinos be at least a part of Dark Matter? What we know about neutrinos - its are almost invisible the same as Dark Matter, right?
Why Dark Matter could not consist of neutrinos?
Ethan Siegel has a good discussion of this question here.  Read that for more detail, but briefly, the main issue is that neutrinos move too fast - they are a form of what cosmologists call &quot;hot dark matter&quot;.  The high speeds mean that they wouldn't settle into dense areas (e.g. galaxies, and clusters of galaxies) as dark matter is observed to do.   Evidence from structures we see in the universe tell us that most dark matter must be cold.
There certainly can be some hot dark matter in the form of neutrinos, but if there were a lot of it, it would leave an imprint on the cosmic microwave background that is not observed, constraining this component to be about 1% of the mass in the universe.