By See Noevo (not verified) on 30 Aug 2016 #permalink
“The most exciting part, from a cosmology point of view, is that the first true galaxy clusters will only form at this particular juncture in the game — between two and three billion years of age — if the Universe is dominated by dark matter… If we hadn’t discovered clusters forming this early, it would’ve posed some big trouble for dark matter; similarly, if we find them when the Universe is only 1 billion years old…that will spell trouble for dark matter, too. Instead, we’re seeing these cosmic behemoths forming exactly where and when they should.”