For a long time, astronomers imagined the early Universe as almost sterilely clean: hydrogen, helium, and almost nothing else. But recent research has revealed a completely different picture. Just 500 million years after the Big Bang, the first galaxies were already scattering carbon, oxygen, and other heavy elements throughout space — the “building blocks” of planets and life. This unexpected conclusion was reached by astronomers at the University of Arizona after analyzing data from the James Webb Space Telescope.

The cosmos’s youth was not so pristine after all

Previously, it was believed that during the era of cosmic dawn, the gas around the first galaxies remained almost pristine — mostly hydrogen and helium. Heavy elements were expected to appear gradually as stars lived out their lives and exploded as supernovae.

New observations paint a different picture. Even at a time when the Universe was only about 3% of its current age, some galaxies were actively producing carbon, oxygen, and silicon and ejecting them into the surrounding space.

“We saw that heavy elements were leaving galaxies very, very early. Galaxies were not only producing these elements, but also dispersing them, possibly ‘seeding’ other galaxies,” says the study’s lead author, Yanda Zhu.

How scientists looked 13 billion years into the past

The team studied the spectra of three extremely distant galaxies. Their light traveled for more than 13 billion years to reach us. To make out the faint absorption lines, nearly 30 hours of Webb observations were required.

The galaxies themselves served as sources of background light. As their radiation passed through the surrounding gas, it left characteristic “fingerprints” — absorption lines. These lines turned out to be blueshifted relative to the galaxies themselves. That means the gas was moving outward, carrying heavy elements with it.

Remarkably, the chemical “fingerprints” around these infant galaxies turned out to be similar to those observed in much more mature systems billions of years later.

Astronomers call the exchange of matter between galaxies and their surroundings the baryon cycle. The new study shows that this cycle was already operating at the very earliest stages.

“Imagine dropping food coloring into a glass of water. The color begins to spread. In the same way, heavy elements from the first galaxies began enriching the surrounding space,” Zhu notes.

What this changes in our understanding

If the gas around galaxies became “contaminated” this early, then truly pristine material — the kind from which the very first stars could have formed (the so-called Population III stars) — disappeared very quickly. These hypothetical objects, composed only of hydrogen and helium, may have existed only briefly and therefore turned out to be extremely rare observational targets.

“If you start with pure vanilla ice cream and almost immediately begin mixing in sprinkles, then very soon you will no longer be able to find plain ice cream without any additions,” Zhu explains figuratively.

The discovery forces us to take a fresh look at how quickly the Universe ceased to be chemically primitive. If heavy elements were spreading so early, then the Universe’s “pristine” era was much shorter than previously thought. And that, in turn, means that the conditions for the emergence of complex chemical compounds were established almost immediately after the birth of the first stars.