All throughout the Universe, there’s more than what we’re capable of seeing. When we look out at the stars moving around within galaxies, the galaxies moving withing groups and clusters, or the largest structures of all that make up the cosmic web, everything tells the same disconcerting story: we don’t see enough matter to explain the gravitational effects that occur. In addition to the stars, gas, plasma, dust, black holes and more, there must be something else in there causing an additional gravitational effect.
Traditionally, we’ve called this dark matter, and we absolutely require it to explain the full suite of observations throughout the Universe. While it cannot be made up of normal matter — things made of protons, neutrons, and electrons — we do have a known particle that could have the right behavior: neutrinos. Let’s find out how much of the dark matter neutrinos could possibly be.