In the heavyweight championship of the cosmos--to decide who gets to be 90 percent of everything--WIMPs have MACHOs on the ropes.
Astronomers can see to the edge of creation and probe the hearts of galaxies, but they can’t account for 90 percent of the mass in the universe. They discovered this somewhat embarrassing state of affairs while observing the rotation of spiral galaxies like our own. If the mass of a galaxy is concentrated where its light is, in the bright core, then just as the sun’s gravity pulls distant Pluto around much more slowly than it pulls Mercury, stars in the outer reaches of a galaxy should orbit much more slowly than stars in the center. But they don’t. The inescapable conclusion is that a galaxy’s mass is not concentrated in its center: there must be some form of matter surrounding the galaxy, in a spheroidal halo, that doesn’t ...
