An international team kept solid gold intact while superheating it to 19,000 Kelvin, about 33,740 °F (18,726 °C). They measured the temperature directly, in real time, and documented the feat in a new study. The result outstrips a long assumed ceiling on how hot a solid can get before it gives way.
The team reached this state with ultra fast laser heating and then checked the atoms with precise X-ray probes.
The work also lays out a clean way to take the temperature of extremely hot, dense matter, which is something that has frustrated experimenters for decades.
What superheating gold means
Lead author Thomas G. White of the University of Nevada, Reno (UNR), led the international collaboration with colleagues at SLAC National Accelerator Laboratory and partner institutions.
The study focuses on superheating, which is when a solid sits above its melting point yet does not melt because the rapid conditions do not give its structure time to reorganize.
Here, the group pushed a thin gold sample far beyond its normal melting threshold in a flash.
The superheated gold remained crystalline for a brief window, long enough to record how fast the atoms were moving and therefore how hot the lattice was.
The work touches a broader frontier known as warm dense matter (WDM), which is a high energy state relevant to planetary interiors and fusion targets.
Accurate temperatures in this regime have been hard to pin down because these hot states are tiny and very short lived.
Why superheating gold matters
In 1988, Hans J. Fecht and William L. Johnson proposed an upper stability boundary called the entropy catastrophe, arguing that a solid cannot be heated much past about three times its melting temperature without melting.
The idea was that as a crystal heats, its entropy rises until it matches the liquid, which should trigger melting.
That back of the envelope limit, about three times the melting point, became the accepted stopping point in textbooks and talks.
It also aligned with the fact that most experiments ran into disordering events at lower temperatures anyway.
The new gold measurements show that ultra fast heating sidesteps those assumptions.
By outrunning processes that normally give a crystal time to expand and unravel, the team produced a much hotter solid phase without violating basic physics.
How the team pushed past the limit
The experiment used a brief pulse, only 45 femtoseconds long, to pump energy into a thin gold foil.
Immediately after this, an intense X-ray pulse captured the atomic motion through tiny shifts in the scattered X-ray frequency. This gave a direct readout of the atoms’ speeds.
Those shifts revealed the gold’s lattice temperature without relying on indirect models.
Because the heating was so swift, the lattice could not expand significantly during the measurement window, and crystalline order persisted for a few trillionths of a second.
The diagnostic hinges on inelastic X-ray scattering (IXS) which, in this fast backscattering geometry, records a clean spectral broadening linked to atomic velocities.
In short bursts, the technique treats the ion motion much like a classical gas and translates the line width into temperature.
Obeying the laws of thermodynamics
Direct temperature tracking matters because warm dense matter only exists for fleeting instants in the lab.
A reliable, model independent measurement gives planetary physicists and fusion researchers a sharper tool to test their calculations.
“It is important to clarify that we did not violate the Second Law of Thermodynamics. [But] the entropy catastrophe was still viewed as the ultimate boundary,” said White.
Outside voices have noted that ultrafast, ultrasmall conditions may not map cleanly onto everyday solids under normal pressure.
Even so, this controlled window lets researchers test long-standing assumptions about melting and stability with far less guesswork.
Heating gold for future technology
Better temperature measurements open doors for modeling planets, where WDM controls how heat moves through cores and mantles. Getting the temperature right helps set the melting curves that guide those models.
Fusion research also stands to gain. In inertial confinement experiments, laser driven targets quickly cross from solid to ultra hot states, and design choices depend on when and how those transitions occur.
There is a materials angle as well. If rapid heating can lift other solids far beyond past expectations without immediate melting, that would invite a rethink of strength, heat capacity, and failure in extreme environments.
The upshot is not that thermodynamics has been tossed out. It is that speed, and the lack of time for expansion, can keep order in place long enough to measure and learn from it.
Future work will likely try different elements, thicker targets, and varied time delays to map exactly when order fails. Each variation will test where the practical limits really lie and how general the no-longer-so- strict ceiling might be.
The full study is published in the journal Nature.
—–
Like what you read? Subscribe to our newsletter for engaging articles, exclusive content, and the latest updates.
Check us out on EarthSnap, a free app brought to you by Eric Ralls and Earth.com.
—–