A string of ancient galaxies has thrown astronomers for a loop by defying standard predictions for the evolution of the universe. The colossal structure hints at possible misunderstandings of how the universe, or maybe mysterious dark matter, behaved shortly after the universe was born.The arc of galaxies is arranged in an easily defined, gravitationally bound superstructure. But it's so old -- forming just 2.8 billion years after the Big Bang -- that astronomers aren’t sure how it had enough time to develop.While the modern universe is full of galaxy clusters, it should not have been that way so long ago. "This is the earliest and largest structure of galaxies that we have ever seen," said Povilas Palunas, an astronomer with the University of Texas and lead author of a report on the study. "And we find it’s a discrepancy with what all models predict for the early universe."Astronomers have long held what they call a hierarchical view of the universe in which dark matter -- invisible stuff up that makes up 90 percent of the material in the universe -- collected in clumps, attracting the interstellar gas that formed the first stars about 200 million years after the Big Bang.

Those stars collected into galaxies, which themselves grouped into clusters and later giant galactic strings.

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