The James Webb Space Telescope (JWST) just keeps on knocking it out of the park. Now, JWST data has allowed an international team of astronomers to confirm the existence of the oldest and most distant galaxies ever captured. The light from these galaxies is more than 13.4 billion years old, which means they formed shortly after the Big Bang when the universe was only 400 million years old, only 2% of its current age.

Several extremely distant galaxies were revealed in the first JWST observations, joining those unearthed by the Hubble Space Telescope. Now that long spectroscopic observations have been made on four of these targets, astronomers can not only confirm that they exist but also learn more about their physical properties.

“We’ve discovered galaxies at fantastically early times in the distant universe,” said Brant Robertson, professor of astronomy and astrophysics at UC Santa Cruz. “With JWST, for the first time we can now find such distant galaxies and then confirm spectroscopically that they really are that far away.”

So how does one tell how old these galaxies are exactly?

Astronomers use something called redshift as a yardstick for how the distance of faraway structures like galaxies. The redshift effect is based on the Doppler effect, which causes the light from distant objects to appear to be moving away from us and to have longer, redder wavelengths. Precise redshift estimates can be obtained through spectroscopy, which dissects the light from an object into its component wavelengths. JWST can perform these measurements

These latest findings found four galaxies with redshifts greater than 10 — a biggie in astronomical terms, and an indication of a faraway object. The Hubble captured redshifts of 10.38 and 11.58 for two galaxies. Those figures have now been verified by the JWST. The Webb was able to go further, however.

Two of the most distant galaxies ever confirmed by spectroscopy were found in JWST images with redshifts of 13.20 and 12.63. A redshift of 13.2 indicates a time period of roughly 13.5 billion years ago.

The observations are the work of scientists who worked together to design and build two of Webb’s instruments, the Near-Infrared Camera (NIRCam) and the Near-Infrared Spectrograph (NIRSpec).

The primary impetus behind the instruments was the quest to learn more about the earliest and faintest galaxies. The JWST Advanced Deep Extragalactic Survey (JADES) is a program proposed by the instrument teams in 2015 that aims to provide a view of the early universe with unprecedented depth and detail.

When JADES first began, NIRCam was used to observe a tiny region of sky near the Hubble Ultra Deep Field for more than 10 days. For over 20 years, astronomers have used virtually every major telescope to study this area. As the JADES team looked at the field in nine different infrared wavelength ranges, they took pictures of nearly 100,000 galaxies billions of light-years away.

The NIRSpec spectrograph was then used for a single three-day observation to gather data on 250 extremely faint galaxies. In addition to providing accurate redshift measurements, this also shed light on the gas and star properties of these galaxies. With these measurements, researchers now know the intrinsic brightness of the galaxies and figure out how many stars exist in the region.

“Now we can start to really pick apart how galaxies are put together over time,” Robertson said.

Robertson estimates that the age at which star formation began in these early galaxies is roughly 225 million years after the Big Bang, which would place the formation of the first stars about 100 million years earlier than previously thought.

These galaxies might not be the oldest discovered for long though. Photometric analyses of JWST images have been used by other teams to find candidate galaxies at even higher redshifts, but these have not been confirmed by spectroscopy.

“It is hard to understand galaxies without understanding the initial periods of their development,” said the University of Cambridge’s Sandro Tacchella and the study’s co-author. “Much as with humans, so much of what happens later depends on the impact of these early generations of stars. So many questions about galaxies have been waiting for the transformative opportunity of Webb, and we’re thrilled to be able to play a part in revealing this story.”