Theorists calculated in the 1960s that galaxies must have been seeded in places where matter had slightly gathered together immediately after the Big Bang, which is thought to have created the Universe several billion years ago.
These fluctuations were seen as ripples in the cosmic background microwave radiation by NASA's Cosmic Background Explorer in 1992, and NASA's Wilkinson Microwave Anisotropy Probe in 2003. But this radiation, which is often described as the afterglow of the Big Bang, originated a mere 400,000 years after the event, long before galaxies formed.
Two sky surveys have now seen evidence of the fluctuations in the separations of galaxies that existed 10 billion years after the Big Bang. This establishes a firm link between primordial instabilities in the Universe and the graininess we see in the cosmos today.
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