James Webb Space Telescope Reveals Unexpected Complex Chemistry In A Primordial Galaxy
University of Arizona astronomers have learned more about a surprisingly mature galaxy that existed when the universe was just less than 300 million years old – just 2% of its current age.
Observed by NASA’s James Webb Space Telescope, the galaxy – designated JADES-GS-z14-0 – is unexpectedly bright and chemically complex for an object from this primordial era, the researchers said. This provides a rare glimpse into the universe’s earliest chapter.
The findings, published in the journal Nature Astronomy, build upon the researchers’ previous discovery, reported in 2024, of JADES-GS-z14-0 as the most distant galaxy ever observed. While the initial discovery established the galaxy’s record-breaking distance and unexpected brightness, this new research delves deeper into its chemical composition and evolutionary state.
The work was done as part of the JWST Advanced Deep Extragalactic Survey, or JADES, a major James Webb Space Telescope program designed to study distant galaxies.
This wasn’t simply stumbling upon something unexpected, said Kevin Hainline, co-author of the new study and an associate research professor at the U of A Steward Observatory. The survey was deliberately designed to find distant galaxies, but this one broke the team’s records in ways they didn’t anticipate – it was intrinsically bright and had a complex chemical composition that was totally unexpected so early in the universe’s history.
“It’s not just a tiny little nugget. It’s bright and fairly extended for the age of the universe when we observed it,” Hainline said.
“The fact that we found this galaxy in a tiny region of the sky means that there should be more of these out there,” said lead study author Jakob Helton, a graduate researcher at Steward Observatory. “If we looked at the whole sky, which we can’t do with JWST, we would eventually find more of these extreme objects.”
Timeline of the universe: Although we are not sure exactly when the first stars began to shine, we know that they must have formed sometime after the era of Recombination, when hydrogen and helium atoms formed (380,000 years after the big bang), and before the oldest-known galaxies existed (400 million years after the big bang). The ultraviolet light emitted by the first stars broke down the neutral hydrogen gas filling the universe into hydrogen ions and free electrons, initiating the era of Reionization and the end of the Dark Ages of the universe. — NASA, ESA, CSA, STScI
The research team used multiple instruments on board JWST, including the Near Infrared Camera, or NIRCam, whose construction was led by U of A Regents Professor of Astronomy Marcia Rieke. Another instrument on the telescope – the Mid-Infrared Instrument, or MIRI, revealed something extraordinary: significant amounts of oxygen.
In astronomy, anything heavier than helium is considered a “metal,” Helton said. Such metals require generations of stars to produce. The early universe contained only hydrogen, helium and trace amounts of lithium. But the discovery of substantial oxygen in the JADES-GS-z14-0 galaxy suggests the galaxy had been forming stars for potentially 100 million years before it was observed.
To make oxygen, the galaxy must have started out very early on, because it would have had to form a generation of stars, said George Rieke, Regents Professor of Astronomy and the study’s senior author. Those stars must have evolved and exploded as supernovae to release oxygen into interstellar space, from which new stars would form and evolve.
“It’s a very complicated cycle to get as much oxygen as this galaxy has. So, it is genuinely mind boggling,” Rieke said.
The finding suggests that star formation began even earlier than scientists previously thought, which pushes back the timeline for when the first galaxies could have formed after the Big Bang.
The observation required approximately nine days of telescope time, including 167 hours of NIRCam imaging and 43 hours of MIRI imaging, focused on an incredibly small portion of the sky.
The U of A astronomers were lucky that this galaxy happened to sit in the perfect spot for them to observe with MIRI. If they had pointed the telescope just a fraction of a degree in any direction, they would have missed getting this crucial mid-infrared data, Helton said.
“Imagine a grain of sand at the end of your arm. You see how large it is on the sky – that’s how large we looked at,” Helton said.
Image
This galaxy was initially selected from ultradeep NIRCam and MIRI imaging with JWST (F770W–F277W–F115W shown as an RGB false-colour mosaic in the lower right). It was targeted for NIRSpec micro shutter array follow-up observations and has been spectroscopically confirmed at redshift Z = 14.32 +0.08-0.20 11. JADES-GS-z14-0 is to the right and the foreground galaxy NIRCam ID 183349 to the left. The apparent colour of JADES-GS-z14-0 is caused by the absorption of the NIRCam/F115W flux by the intervening IGM and the rest-frame optical nebular emission-line excess in MIRI/F770W relative to NIRCam/F277W. A scale bar of 0.6″ is provided which corresponds to roughly 1.9 physical kpc (pkpc) at the observed redshift (z = 14.32).– Nature Astronomy
The existence of such a developed galaxy so early in cosmic history serves as a powerful test case for theoretical models of galaxy formation.
“Our involvement here is a product of the U of A leading in infrared astronomy since the mid-’60s, when it first started. We had the first major infrared astronomy group over in the Lunar and Planetary lab, with Gerard Kuiper, Frank Low and Harold Johnson,” Rieke said.
As humans gain the ability to directly observe and understand galaxies that existed during the universe’s infancy, it can provide crucial insights into how the universe evolved from simple elements to the complex chemistry necessary for life as we know it.
“We’re in an incredible time in astronomy history,” Hainline said. “We’re able to understand galaxies that are well beyond anything humans have ever found and see them in many different ways and really understand them. That’s really magic.”
Photometric detection at 7.7 μm of a galaxy beyond redshift 14 with JWST/MIRI, Nature Astronomy (open access)
Astrobiology, Astrochemistry,
