Astronomers confirmed that four ancient galaxies detected by the James Webb Space Telescope in the early months of its operations are the oldest scientists have ever seen and nearly as old as the universe itself.
The galaxies were among hundreds of promising stellar conglomerations found in images from the Near Infrared Camera (NIRCam) aboard the James Webb Space Telescope (Webb or JWST). But scientists were only able to confirm that these ancient objects really were as old as they appeared after they looked at them in detail with the Near Infrared Spectrograph, which revealed their chemical composition and determined how fast these galaxies are moving away from Webb.
The astronomers now know that light from the four galaxies took more than 13.4 billion years to reach Webb. More precisely, the telescope sees the galaxies as they looked only 350 million years after the Big Bang, when the universe was only 2% of its current age, although the galaxies must have started to form even earlier.
Observing such young stellar families is exactly what Webb was built for, and scientists are excited that it began delivering such fascinating results so early in its operations.
"These [galaxies] are well beyond what we could have imagined finding before JWST," Brant Robertson, an astrophysicist at the University California Santa Cruz and one of the researchers involved in the observations, said in a statement. "With JWST, for the first time we can now find such distant galaxies and then confirm spectroscopically that they really are that far away."
To confirm that the galaxies really were as old as they seemed, astronomers had to obtain precise estimates of the so-called redshift from NIRSpec's data. Redshift makes objects that are moving farther away from us appear redder as a result of the expansion of the universe, which stretches the light emitted by distant stars and galaxies into longer, redder wavelengths of the light spectrum.
The most distant of the galaxies detected by Webb displayed a redshift of 13.2, which corresponds to an age of about 13.5 billion years — the highest ever measured for any galaxy.
"At redshift 13, the universe is only about 325 million years old," Robertson said.
The observations were conducted as part of the JWST Advanced Deep Extragalactic Survey (JADES) project, which uses NIRCam and NIRSpec to study the early universe in ways that were impossible before.
An international collaboration of more than 80 astronomers, JADES is only at the beginning of its endeavor. Next, the astronomers want to look at individual stars in those galaxies, some of which may have been born up to 100 million years earlier than the age at which they are seen by Webb.
"With these measurements, we can know the intrinsic brightness of the galaxies and figure out how many stars they have," Robertson said. "Now we can start to really pick apart how galaxies are put together over time."
The observations match what astronomers expected based on existing galaxy formation models, Robertson added.
In the NIRCam observations, the team also identified galaxies that appear even older than those now confirmed, but the ages of those have not yet been verified by the more accurate spectroscopic measurements from NIRSpec.
The new findings will be presented on Monday (Dec. 12) at a Space Telescope Science Institute conference in Baltimore.