According to the WMAP, 23 percent of the universe is made of a strange, undetermined substance called dark matter, which has weight, surrounds the galaxies in a gigantic halo, but is totally invisible. Dark matter is so pervasive and abundant that, in our own Milky Way galaxy, it outweighs all the stars by a factor of 10. Although invisible, this strange dark matter can be observed indirectly by scientists because it bends starlight, just like glass, and hence can be located by the amount of optical distortion it creates.
