A map of the distribution of galaxies in a thin wedge on the sky,
from the Sloan Digital Sky Survey (SDSS-II). The earth is at the
vertex of the wedge, and the most distant objects shown are
1.3 billion light years away. Red points mark galaxies whose light
is dominated by old stars, while blue points show galaxies with
younger populations of stars. Galaxies are arrayed in clumps,
filaments, and sheets, which are interweaved with bubbles and
tunnels, the cosmic voids. The new study shows that these voids
are empty of massive dark matter halos as well as luminous galaxies,
and that the numbers and sizes of voids agree with theoretical
models in which they grow by gravity starting from a smooth
distribution of dark matter in the early universe.
Credit: M. Blanton and the SDSS.