Smashing Oxygen Remade the Big Bang's First Soup

The Big Bang's First Soup just got easier to cook up in a laboratory. Physicists working with the STAR experiment at the Relativistic Heavy Ion Collider smashed oxygen nuclei together at nearly the speed of light and found strong evidence that the collisions produced a quark-gluon plasma — the hot, dense matter that filled the universe in its first microseconds, according to the Brookhaven National Laboratory.

The clue is a phenomenon called jet quenching. When two nuclei collide, they spit out back-to-back jets of energetic particles. If a quark-gluon plasma forms, one jet escapes easily from the plasma's edge while its partner, forced to travel farther through the hot soup, loses energy and fades. The new data, just published in Physical Review Letters, show that signature clearly in oxygen-on-oxygen collisions.

The result matters because this plasma is believed to be the form of matter that filled the early universe before the protons and neutrons that make up today's atoms ever formed. Understanding its properties is essential for uncovering how the early universe evolved in its first moments. "One of the most powerful ways scientists study the QGP is by identifying where its signatures appear — and just as importantly, where these signatures turn off," said Li Yi, a physics professor at Shandong University who oversaw the analysis.

Spotting the soup is an indirect art. The plasma survives for only a sliver of a second, so no detector can photograph it directly. Instead, the STAR detector watches the debris: the spray of particles flying out of each smashup. By comparing jets that took the short path out with ones that plowed through the fireball, physicists can read the energy loss like a fingerprint of the medium they crossed.

A new lower limit for the primordial soup

Jet quenching has long been one of the smoking-gun signatures of plasma formation in collisions of large atomic nuclei at the collider. It has also been observed in oxygen-oxygen collisions at the Large Hadron Collider at CERN, which operates at far higher energies. The new analysis, performed at significantly lower collision energy, sets a new lower boundary for the conditions capable of producing the primordial plasma in a small collision system.

That small-system detail is the headline for physicists. Earlier runs at the Long Island lab revealed that even tiny collision systems can briefly form droplets of the soup, overturning older ideas that it only appears in the most violent smashups. Big Bang's First Soup now has a confirmed lower limit in gentler collisions than ever before — which tells researchers the primordial state is easier to reach than once assumed.

A quarter century ends with a final run

The result is also a farewell note. The collider operated from 2000 until earlier this year, and its final oxygen collisions were recorded in February 2026 by the STAR and sPHENIX detectors, closing out a quarter century of operations. The machine's tunnel and many of its components will now pass to its successor, the Electron-Ion Collider, which is designed to probe the inner structure of protons and neutrons.

The successor machine will collide electrons with ions rather than smashing nuclei head-on, giving physicists a cleaner look at how quarks and gluons arrange themselves inside protons. Because construction reuses the existing tunnel, the long run of accelerator work on the same site directly paves the way for the next era of nuclear physics there.

For the rest of us, the takeaway is almost poetic. Every proton and neutron in your body condensed out of this exact kind of soup as the infant universe cooled — and physicists are still mapping the precise conditions where the soup switches on and off, which is how they reconstruct those earliest instants. The researchers describe their finding as strong evidence rather than a closed case: each new collision system adds a data point, and the hunt continues for the exact threshold where the primordial state vanishes.

It is a reminder that the biggest questions in physics are still being answered with giant machines and patient data. From ancient impacts that reshaped coastlines to lab tweaks that change how food tastes, the through line of this week's science is the same: careful measurement keeps rewriting what we thought we knew. Full details are in the lab's official announcement and in further reporting on the result.