Far-flung: glimpse of fledgling galaxy (Image: CLASH team/The Space Telescope Science Institute)

Using a cosmic magnifying glass, astronomers have uncovered the best contender yet for the most distant known galaxy – an object from which light began travelling towards us 13.2 billion years ago. The find adds a precious piece to the largely unsolved puzzle of what the universe looked like just a few hundred million years after the big bang.

Observations show that when the cosmos was 400,000 years old it was a sea of atoms. By the time it was a billion years old, it was teeming with galaxies. Figuring out what happened in the intervening years is difficult because objects from so long ago are very faint when viewed from Earth.

Dubbed MACS 1149-JD, the new galaxy was spotted using a technique called gravitational lensing. Wei Zheng of Johns Hopkins University in Baltimore, Maryland, and colleagues used the Hubble Space Telescope to scrutinise nearby galaxy clusters in the hope that the clusters’ gravity would bend and magnify the light of more distant background objects.


Behind the most massive of the 12 observed clusters, the team found a galaxy whose light appears to have left it when the universe was just 490 million years old. “Because the object was magnified by Mother Nature’s lens by a factor of more than 10, we detect this object much easier,” says Zheng.

Primitive colours

Only one other known galaxy, UDFj-39546284, appears to come from the same era, although its distance is more uncertain.

Astronomers estimate distances for very far-off objects by calculating their redshift, the degree to which their light has been stretched toward the red end of the spectrum as it travels across the expanding universe. UDFj-39546284 was seen at only one wavelength band, while MACS 1149-JD was detected at five, giving scientists more data for making a better redshift measurement.

Neither galaxy is bright enough to produce a spectrum – the gold standard for measuring distances, says Richard Ellis of the California Institute of Technology in Pasadena. Still, the colour-based estimate for the new find is “reasonably convincing”, he says, adding: “An object like this is very important because it gives us a glimpse of when the first galaxies switched on.”

Even though we see MACS 1149-JD as it was 490 million years after the big bang, its colour suggests that its stars formed up to 200 million years earlier.

“That means the object was there in a primitive form when the universe was only 300 million years old,” says Ellis.

Future observatories, such as the James Webb Space Telescope, could find and characterise many of these primordial galaxies, which might offer clues to whatever kick-started a process called reionisation.

This is when the opaque fog of neutral hydrogen that permeated the early universe was ionised by an unknown radiation source, making the gas transparent to light. Candidate sources include fledgling galaxies, massive black holes or perhaps the decay of exotic particles.

Journal reference: Nature, DOI: 10.1038/nature11446