Peering through a thinning fog of hydrogen, the Hubble Space Telescope has taken the first census of the earliest known galaxies in the universe. One is the most distant galaxy yet spotted â€“ so far away that its light has taken 13.4 billion years to reach us.
Hubble’s survey of fledgling galaxies can help us figure out what drove a phenomenon called reionisation. It ended a mysterious time called the cosmic dark ages, when a shroud of opaque hydrogen gas dominated the universe. Then radiation, probably from the first stars and galaxies, ionised the hydrogen and made it transparent, but details of precisely how this happened are scarce.
The galaxies date from the middle of the reionisation era, when the universe was about 500 million years old. “This study represents the deepest archaeological dig of the universe so far,” says Avi Loeb of Harvard University, who was not involved in the survey.