The static speed of light assures that astronomers see faraway galaxies not as they are, but as they existed long ago. The same is true about the matter (regular or dark) that surrounds these ancient galaxies.
Astronomers recently used this knowledge — as well as a cosmic signal sent out shortly after the Big Bang — to map how dark matter was distributed around galaxies some 12 billion years ago. In short, they found the dark matter was less 'clumpy' than expected, which, if confirmed, would suggest that many accepted models of cosmology are due for revisal.
