Astronomers peering far back in time through the eyes of the Hubble Space Telescope have detected a group of infant galaxies being thrust together by the power of mysterious dark matter when the universe was young.
That "protocluster" is the most distant galactic event astronomers have ever seen, they say.
An international team of stargazers spotted the five bright galaxies moving together during a routine sky survey, and determined that the clustering they were seeing occurred more than 13 billion years ago.
Most galaxies today lie within clusters that have long since formed, and our Milky Way itself is part of a group that includes the Andromeda galaxy plus another known as Messier 87 and more than 50 smaller ones. They are all part of the Virgo "supercluster" of more than 2,000 galaxies that lie in the distant night sky far beyond the constellation Virgo.