Star-forming galaxy is the most distant ever found
Such is often the case for galaxies, at least: the first
galaxies were small, then eventually merged together to form the behemoths we
see in the present universe.
Those smaller galaxies produced stars at a modest rate; only
later—when the universe was a couple of billion years old—did the vast majority
of larger galaxies begin to form and accumulate enough gas and dust to become
prolific star factories. Indeed, astronomers have observed that these star
factories—called starburst galaxies—became prevalent a couple of billion years
after the Big Bang.