In the short time it has been operating, NASA’s James Webb Space Telescope (JWST) has unlocked a new realm of astronomy. It can peer farther into the cosmos, detecting objects too faint to appear in less powerful telescopes. A pair of new studies explore two such objects, which are believed to be among the oldest galaxies in the universe. These objects could add greatly to our understanding of the early universe and could also force astronomers to reevaluate some of what we thought we knew.
The newly discovered galaxies are visible in a galaxy cluster called Abell 2744, which is about 3.5 billion light years away. However, they’re not inside Abell 2744. They’re actually several billion light years behind the cluster, but gravitational lensing magnified their signature, allowing the JWST to spot them. The Hubble Space Telescope imaged this same region several years ago, but its optics were not able to detect the faint light from these ancient objects.
The studies, led by Marco Castellano of the National Institute for Astrophysics in Rome and Rohan Naidu of the Harvard-Smithsonian Center for Astrophysics, report the galaxies existed just a few hundred million years after the Big Bang. Astronomers can tell these galaxies are old because they have extreme redshifts of 10.5 and 12.5 — the universe is expanding, which causes light from distant objects to stretch out. The larger the redshift, the older the source. At 10.5 and 12.5, these galaxies appear in the image as they did 450 million and 350 million years after the Big Bang, respectively.
The two ancient galaxies highlighted in Webb deep field images.
“These galaxies would have had to have started coming together maybe just 100 million years after the Big Bang. Nobody expected that the dark ages would have ended so early,” said Garth Illingworth, who worked on one of the studies. While these distant star clusters are too dim for Hubble to spot, they’re actually much brighter than they should be. The consensus has long been that few galaxies would have existed at this time, and those that did would have been small and dim.
There are two possible explanations for this; the galaxies could be much larger than expected with various low-mass stars like alter galaxies, or they could be small and filled with high-mass Population III stars that are each much brighter than most stars today. Before we rethink the early universe, more observations are required. The estimates of distance in the new studies are based on measuring infrared colors, but future work will make follow-up spectroscopy measurements that will either confirm or refute those numbers. However, there is a growing body of evidence that bright galaxies did exist at this time. A previous Webb discovery pointed to a similarly aged galaxy dubbed Maisie’s Galaxy, with a redshift of 11.8.
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