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In a sky survey made in near-infrared light Hubble has spotted five galaxies clustered together. They are so distant that their light has taken 13.1 billion years to reach us. These galaxies are among the brightest galaxies at that early stage of the Universe’s history. They are also very young: we are seeing them just 600 million years after the Universe’s birth in the Big Bang.
Galaxy clusters are the largest structures in the Universe, comprising hundreds to thousands of galaxies bound together by gravity. This developing cluster, or protocluster, seen as it looked 13 billion years ago, presumably has grown into one of today’s massive cities of galaxies, comparable to the nearby Virgo cluster of more than 2000 galaxies.
“These galaxies formed during the earliest stages of galaxy assembly, when galaxies had just started to cluster together,” says the study’s leader, Michele Trenti (University of Cambridge, UK and University of Colorado at Boulder, USA). “The result confirms our theoretical understanding of the buildup of galaxy clusters. And, Hubble is just powerful enough to find the first examples of them at this distance.”