Another 23 % consists of mysterious dark matter that (so far) manifests itself only through its gravity. (sciencemag.org)
20 % of our universe is made up of your run - of - the - mill matter, while 80 % of mysterious dark matter, which we know very little about. (bigthink.com)
Unseen right - handed neutrinos may also account for mysterious dark matter. (newscientist.com)