Like a whirlpool, the center of a spiral galaxy rotates faster than the outside. If the galaxy were made up only of visible matter, its outer reaches would rotate at a predictably slower rate. But the visibly outer edge of the galaxy rotates much faster than it should, indicating the presence of enormous quantities of phantom matter. Encountering the Invisible As Earth revolves around the sun, it theoretically passes through a wind of dark matter. Because the planet moves in different directions at different times of the year, the collisions with dark matter should vary with the seasons.
None can constitute more than a fraction of dark matter.
There are about 2,000 in every cubic inch of the cosmos. But they move so fast that galaxies probably wouldn't have formed with appreciable mass in a torrent of neutrinos. There should be about 100,000 per cubic inch in the galactic halo, if they actually existed and could be detected. Predicted by a popular theory that says all the particles now known once had matching counterparts at the stupendous energy densities that prevailed just after the Big Bang. As the cosmos cooled, all the particles disappeared except the lightest ones.