The James Webb Space Telescope (JWST) has discovered not one, but two of the earliest and most distant galaxies ever seen, continuing to break the records it previously set.
The most distant galaxy, JADES-GS-z14-0, is seen as it was about 300 million years after the Big Bang, existing at least 100 million years earlier than the previous record holder. This means that the light seen by JWST from this primordial galaxy has traveled 13.5 billion years on its way to reach us.
JADES-GS-z14-0 is not alone. It was discovered along with another galaxy, JADES-GS-z14-1, which is almost as far away and ranks second in the ranking of the earliest galaxies ever seen by mankind.
Connected: The James Webb Space Telescope discovers 3 of the earliest galaxies in our universe
The announcement of the discoveries, made in October 2023 and January 2024, are the latest developments in the ongoing investigation of cosmic dawn that the $10 billion telescope has helped as part of the JWST Advanced Deep Extragalactic Survey (JADES) program. JADES aims to provide vital insights into the ways in which stars, gas and black holes were evolving in primitive galaxies when the 13.8-billion-year-old universe was very young.
“These galaxies join a small but growing population of galaxies from the first half billion years of cosmic history where we can really probe the stellar populations and distinctive chemical element patterns within them,” team member and Kavli Cosmology Institute scientist Francesco D’ Eugenio said in a statement.
However, JADES-GS-z14-0 is not only remarkable for how far it is from Earth and how early it existed in the cosmos. At about 1,600 light-years across, this “cosmic dawn” galaxy is also remarkable for how large and bright it is.
“The size of the galaxy clearly proves that most of the light is produced by a large number of young stars, rather than material falling into a supermassive black hole at the center of the galaxy, which would [make it] appear much smaller,” JADES team leader Daniel Eisenstein of the Harvard & Smithsonian Center for Astrophysics (CfA) said in a separate statement.
The extreme brightness of JADES-GS-z14-0 and the fact that this brightness is powered by young stars means that this galaxy represents the most striking evidence for the rapid formation of large, massive galaxies in the early universe yet found .
JADES team member and University of California-Santa Cruz researcher Ben Johnson added that JADES-GS-z14-0 shows that galaxy formation in the early universe was very fast and intense.
“JWST will allow us to find more of these galaxies, perhaps when the universe was even younger,” he said. “It’s a wonderful opportunity to study how galaxies begin.”
The James Webb Space Telescope sees red to spot early galaxies
JWST is able to see early galaxies thanks to the high infrared sensitivity of its instruments, especially its main imager, the Near-Infrared Camera (NIRCam).
Light leaves these cosmic dawn galaxies with a wide range of wavelengths similar to light from galaxies closer to the Milky Way. It is the billions of years of travel that transforms this light into low-energy, long-wavelength light in the near-infrared and infrared regions of the electromagnetic spectrum.
The fabric of space itself is expanding, and as light passes through it, its wavelength stretches along with it. This causes the light to be “shifted” down into the red end of the electromagnetic spectrum, hence the name for this phenomenon, “red shift”.
Galaxies that are farther away have to pass through more space (which is stretching as it expands) before their light reaches us, and thus, that light experiences more redshift. Consequently, the redshift, denoted z, can be used to measure the distance to celestial objects with a known spectrum. And because light takes a finite time to travel, this distance can be used to calculate how long ago these galaxies as we see them existed.
JADES-GS-z14-0 has a redshift of z = 14.32, while the previous most distant galaxy, JADES-GS-z13-0, has a redshift of z = 13.2, which placed it as existing 400 million years after the Big Bang. Clearly, this newly found galaxy has absolutely smashed that record, with JWST looking back another 100 million years.
“JADES-GS-z14-0 now becomes the archetype of this phenomenon,” said JADES collaboration team member Stefano Carniani of the Scuola Normale Superiore. “It’s amazing that the universe can create such a galaxy in just 300 million years.”
JADES-GS-z14-0 made some surprises
Not everything about JADES-GS-z14-0 was immediately clear to the JADES team, and several elements may confound our view of the early cosmos.
When first seen, the primordial galaxy was so close to a nearby foreground galaxy that the team suspected they might be celestial neighbors. This idea was dispelled last October when the JADES crew spent five days performing an in-depth analysis of JADES-GS-z14-0 with NIRCam. Applying filters specifically tailored to identify early galaxies confirmed the extreme distance to JADES-GS-z14-0.
“We just couldn’t see any plausible way to explain this galaxy as just a neighbor of the nearest galaxy,” said JADES team member and University of Arizona researcher Kevin Hainline.
The galaxy also surprised its discoverers because its light is even redder than expected. That’s because the light from JADES-GS-z14-0 is being “reddened” by the dust inside it that will become the building blocks of stars that will help this galaxy grow even bigger.
Another surprise was the discovery of oxygen in JADES-GS-z14-0. Elements heavier than hydrogen and helium are forged by stars during their lifetime and then scattered throughout galaxies when these stars explode. The observation of oxygen in JADES-GS-z14-0 may indicate that at least one generation of stars has already lived and died in this very early galaxy.
“All these observations, together, tell us that JADES-GS-z14-0 is not like the types of galaxies that are predicted by theoretical models and computer simulations to exist in the very early universe,” JADES researcher Jake Helton of Steward. Observatory and the University of Arizona said. “Given the observed luminosity of the source, we can predict how it might grow over cosmic time, and so far, we have not found any suitable analogues from the hundreds of other high-redshift galaxies we have observed in the survey ours.”
Helton added that given the relatively small region of the sky that JWST searched to find JADES-GS-z14-0, its discovery has profound implications for the predicted number of bright galaxies we see in the early universe.
“It is likely that astronomers will find many such bright galaxies, perhaps even at earlier times, over the next decade with JWST,” he concluded. “We are thrilled to see the incredible diversity of galaxies that existed at the cosmic dawn!”