A team of researchers has successfully measured liquid carbon — a mysterious and extreme state of matter — using cutting-edge lasers and X-ray technology. This seems to mark the first time scientists have directly observed the internal structure of carbon in its liquid form, a state found deep inside planets and relevant to future clean energy technologies like nuclear fusion.
The experiment, led by the University of Rostock and Helmholtz-Zentrum Dresden-Rossendorf (HZDR), took place at the European XFEL, the world’s largest X-ray laser facility in Germany. Results were recently published in Nature.
Carbon only exists in its liquid form under extreme pressure and temperatures above 4,500°C, making it almost impossible to study in laboratories. This is the highest known melting point of any element — and no container could survive those conditions.
Yet understanding liquid carbon is key for:
- Modeling planetary interiors (like those of gas giants or carbon-rich exoplanets)
- Advancing nuclear fusion research, which could one day provide clean, limitless energy
- Improving our knowledge of material behavior under extreme conditions, which affects everything from energy systems to waste treatment under high pressure.
To get around the containment problem, the team used a high-power laser (DIPOLE 100-X) to compress a tiny piece of solid carbon just enough to briefly turn it into liquid — for only a few nanoseconds (billionths of a second).
At that precise moment, they fired an ultrashort X-ray pulse from the European XFEL to capture how atoms were arranged in the liquid. By repeating this many times with different timing, the researchers essentially made a “movie” of carbon melting in real time.
This is seemingly the first experiment to combine laser compression, ultrafast X-ray diffraction, and high-resolution detectors, in a way that can capture matter in extreme states with this level of detail.
The structure of liquid carbon resembles that of solid diamond, with each atom bonded to four others — an unusual property for a liquid.
It behaves similarly to water in terms of having unique structural properties, like dynamic bonding.
The team also pinpointed the melting point of carbon more precisely than ever before, resolving previous discrepancies in theoretical models.
Quite apart from the greater light it sheds on the behaviour of carbon, the breakthrough is said to open a new era in high-pressure science. According to the researchers, the same method could soon be applied to other materials critical for energy, waste processing, or planetary science.
As data processing and automation improve, what currently takes hours of lab time could soon be done in seconds, vastly speeding up research.
“We now have the toolbox to characterize matter under highly exotic conditions in incredible detail,” said Dr. Ulf Zastrau, lead of the High Energy Density (HED) group at European XFEL.
