Galaxy distribution. Two theoretical models of how the large-scale distribution of galaxies evolved compared with the real distribution. The circle at bottom (gold) shows observed galaxies within 150 million light years of Earth. The two computer- generated models assume that most of the matter in the Universe consists of dark matter. In the cold dark matter scenario (blue) galaxies form from the collisions of small proto-galaxies. In the hot dark matter scenario (green) the first objects to form are superclusters of matter which then fragment to form galaxies. The cold dark matter model is clearly closer to the real distribution of galaxies we observe in the sky.