Researchers at Brookhaven’s RHIC have, for the first time, precisely measured the emission temperature of quark–gluon plasma produced by colliding gold nuclei: about 3.3 trillion °C (≈5.94 trillion °F), roughly 220,000 times hotter than the Sun’s core. The team inferred this temperature by measuring electron–positron pairs from photon conversions recorded in the STAR detector. Published in Nature Communications, the result helps scientists map how the early universe cooled from a quark–gluon plasma into the particles that form atoms.
3.3-Trillion-Degree 'Particle Soup': Scientists Recreate the Universe Moments After the Big Bang
Researchers at Brookhaven’s RHIC have, for the first time, precisely measured the emission temperature of quark–gluon plasma produced by colliding gold nuclei: about 3.3 trillion °C (≈5.94 trillion °F), roughly 220,000 times hotter than the Sun’s core. The team inferred this temperature by measuring electron–positron pairs from photon conversions recorded in the STAR detector. Published in Nature Communications, the result helps scientists map how the early universe cooled from a quark–gluon plasma into the particles that form atoms.
04:38 AM, 11/16/2025Science
Researchers measure the hottest matter ever made on Earth
For 25 years, physicists at Brookhaven National Laboratory have used the Relativistic Heavy Ion Collider (RHIC) to slam gold nuclei together at near-light speeds and briefly produce the hottest matter ever created in the laboratory. That fireball is a quark–gluon plasma — a fleeting "particle soup" that mirrors conditions in the universe a few microseconds after the Big Bang. Researchers now report the first precise measurement of the temperature at which this matter emits photons.
When the gold nuclei collide inside RHIC’s STAR (Solenoidal Tracker at RHIC) detector, protons and neutrons melt into free quarks and gluons. This plasma exists for only a split second, then cools and sprays out many particles. Some of the emitted photons convert into electron–positron pairs, and by measuring the mass distribution of those pairs scientists can infer the photons’ energies and thus the temperature at emission.
Using that technique, the team determined an emission temperature of about 3.3 trillion °C (≈5.94 trillion °F) — roughly 220,000 times hotter than the Sun’s core. The result was published in Nature Communications and provides a direct experimental handle on the conditions that governed the earliest moments of the universe.
“These are the building blocks of the particles that make up the visible world, and we’re trying to figure out how they work,” — Zhangbu Xu, Brookhaven National Laboratory and Kent State University.
The new temperature measurement helps physicists narrow down when and how the early universe transitioned from quark–gluon plasma into the composite particles that later formed atoms. These transformations are viewed as fundamental phase changes in matter, analogous to ice melting into water but involving the strong force and subatomic constituents.
RHIC and the STAR experiment — after 25 years of operation — are entering the final months of their current run. The facility will pause to make way for the larger Electron–Ion Collider, scheduled to come online in the early 2030s. Meanwhile, scientists will continue mining STAR’s final datasets to refine this measurement and to map the most fundamental phase diagram of matter.
Why this matters: A precise temperature for quark–gluon plasma anchors theoretical models of the strong force, helps validate simulations of the early universe, and guides future experiments probing how ordinary matter emerged from the primordial fireball.