"It's not quite time for theorists to panic, but we're getting there," said astronomer Roberto Abraham of the University of Toronto, Canada, after announcing his group's discovery of a startling number of mature galaxies in the young universe. But although the finding seemed to undermine the standard view of how matter assembled, theorists have respectfully declined to sound the alarm. Abraham and several colleagues described the newly finished Gemini Deep Deep Survey, an ambitious program with the 8-meter Gemini North telescope at Mauna Kea, Hawaii. The survey is among many efforts worldwide to examine large numbers of galaxies that existed when the cosmos was a fraction of its current age. Such galaxies, astronomers have assumed, trace the way that gravity segregated matter through space as the universe aged. And according to reigning theoretical models, clumps and webs of matter grew until galaxies arose inside massive halos of invisible dark matter. In that "hierarchical" picture, shards of protogalaxies took billions of years to merge and assemble the grand spirals and giant elliptical blobs we see today.
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