Slurping up cold streams of star fuel, some of the Universe's first galaxies got fat quickly, new observations suggest. The findings could overturn existing models for the formation and evolution of galaxies that predict their slow and steady growth through mergers.
Researchers using the Subaru telescope in Hawaii have identified five distant galaxy clusters that formed five billion years after the Big Bang. They calculated the mass of the biggest galaxy in each of the clusters and found, to their surprise, that the ancient galaxies were roughly as big as the biggest galaxies in equivalent clusters in today's Universe. The ancient galaxies should have been much smaller, at only a fifth of today's mass, based on galaxy-formation models that predict slow, protracted growth. “That was the reason for the surprise — that it disagrees so radically with what the predictions told us we should be seeing,” says Chris Collins of Liverpool John Moores University in Birkenhead, UK. Collins and his colleagues publish the work today in Nature.