The James Webb Space Telescope’s (JWST) surprise findings about the early universe may soon help explain why scientists can’t locate the first stars.
University of Arizona astronomers recently published a paper in Nature Astronomy revealing that unexpectedly heavy elements existed a mere 500 million years after the Big Bang, when the universe was only about 3% of its current age.
Due to speed-of-light constraints, the JWST’s gaze toward the edges of the universe also provides a look back in time to the early universe, which has proven to be full of cosmic surprises. Among those JWST findings is the emerging picture of a much more complex early universe than the pristine clouds of helium and hydrogen astronomers expected to find.
JWST Surprises Astronomers
Data collected by the JWST unexpectedly revealed that the early universe contained much more oxygen and carbon than previously assumed, two heavy elements that surprised astronomers.
“We observed that heavy elements escaped from galaxies very, very early in cosmic time,” said first author Yongda Zhu, a postdoctoral researcher in the U of A Department of Astronomy and Steward Observatory. “Not only were the galaxies producing these elements, but they were also dispersing them, possibly seeding other galaxies.”
At the top of the periodic table sit the simplest and lightest elements: hydrogen and helium. These were also the first elements to form, and therefore all that astronomers had expected to find at so remote a period. First, these had to form stars to produce the powerful nuclear forces that create heavier, more complex elements further down the periodic table.
Seeding the Universe
Through the lives and deaths of those first generations of stars, including supernova explosions, the universe was seeded with heavier elements. Scientists knew these elements, including carbon, later became incorporated into new stars, solid planets, and eventually life itself, yet exactly how they spread throughout the early universe remained unclear.
The team’s research focused on a period of the universe called the Epoch of Reionization, involving observations of galaxies whose light traveled for roughly 13 billion years before reaching JWST. This period is named for the reionization of hydrogen gas between stars and galaxies, a process that gradually made the universe increasingly transparent to ultraviolet light.
“We used the galaxies themselves as background light sources,” said Zhu. “As light from the galaxies traveled toward Earth, it passed through surrounding gas, and we were able to look at the light’s absorption patterns to detect specific elements.”
It took JWST 30 hours of exposure to detect the faint spectra of these ancient galaxies. For the research, Zhu began by manually searching public repositories of JWST spectra until he discovered three, among hundreds he viewed, with blueshifted absorption patterns suggesting heavier elements were present.
Analyzing JWST Observations
The spectral fingerprints associated with these galaxies were surprisingly similar to those seen much later in cosmic history, suggesting heavier elements were produced and dispersed much closer to the cosmic dawn than astronomers had believed.
In their analysis of the JWST data, the researchers found evidence that a process called baryon cycling helped spread heavy elements throughout the early universe. In this process, matter flows into and out of galaxies, allowing material produced by stars to be recycled and dispersed into their surroundings.
“Think of these elements, which originated from the galaxies’ stars, as food dye dropped into a cup of water,” said Zhu. “The color begins to spread through the water, and, in a similar fashion, these heavy elements from early galaxies began to escape into space and ‘enrich’ their surroundings.”
The researchers suggest this rapid enrichment could help explain why pristine gas associated with the universe’s earliest generations of stars has proven so difficult to find. If heavy elements were produced and widely dispersed extremely early in cosmic history, they could have enriched much of the surrounding gas before astronomers are able to observe it directly.
The paper, “Early Metal-Enriched Baryon Cycling Before the Midpoint of Cosmic Reionization,” appeared in Nature Astronomy on September 24, 2026.
Ryan Whalen covers science and technology for The Debrief. He holds an MA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.