How Much Of The Dark Matter Could Neutrinos Be?
“If we restrict ourselves to the Standard Model alone, we simply cannot account for the dark matter that must be present in our Universe. None of the particles we know of have the right behavior to explain all of the observations. We can imagine a Universe where neutrinos have relatively large amounts of mass, and that would result in a Universe with significant quantities of dark matter. The only problem is that dark matter would be hot, and lead to an observably different Universe than the one we see today.
Still, the neutrinos we know of do behave like dark matter, although it only makes up about 1% of the total dark matter out there. That’s not totally insignificant; it equals the mass of all the stars in our Universe! And most excitingly, if there truly is a sterile neutrino species out there, a series of upcoming experiments ought to reveal it over the next few years. Dark matter might be one of the greatest mysteries out there, but thanks to neutrinos, we have a chance at understanding it at least a little bit.”
Dark matter is a form of matter that gravitates, but neither absorbs nor emits light, and has been frustratingly difficult to pin down and directly detect. There’s a known particle that has exactly those same properties: the neutrino! You might wonder, then, if perhaps neutrinos had the right value of mass and number, if they could make up the dark matter? And if not all of it, could they at least make up part of it? This is a question that astronomers and physicists have pondered for decades, and we might be closer than ever to the actual answer.