Gold 'survives' at 18,700°C, overturning 40-year-old physics theory

For the first time, scientists have directly measured the temperature of atoms in matter at extreme conditions, shattering a four-decade-old theory about the superheating limit of solids.

At the SLAC laboratory (USA), a team of scientists used extremely powerful lasers and super-bright X-rays to heat gold to 19,000 kelvin (about 18,727°C), more than 14 times higher than the melting point of this material, while the gold remained solid. The results not only redefine the limits of matter, but also open up new research directions on planetary structure, fusion energy and high-energy density physics.

Great meaning

Matter at extremely high temperatures, such as plasma on the Sun or deep inside planets, often reaches a state called 'warm dense matter' with temperatures of hundreds of thousands of kelvin. Previously, their temperatures could only be estimated, with huge uncertainties.

The new method at SLAC directly measures the speed at which atoms vibrate using X-rays to calculate temperature. In the first experiment, they heated solid gold far beyond its predicted temperature limit, challenging theories from the 1980s.

The powerful laser heats up a thin gold sample in trillionths of a second. The atoms vibrate faster as the temperature increases. X-rays from the LCLS source sweep through, their frequency slightly shifted by the atomic vibrations, allowing the temperature to be determined precisely.

The team found that gold could reach 19,000 kelvin and still remain solid, far exceeding the 'entropy catastrophe limit' – the point at which all solids lose their structure. The trick is to heat it so quickly that it doesn't have time to expand and melt.

The discovery suggests that materials can be superheated to unprecedented levels, if the heating rate is fast enough. The new knowledge promises to improve understanding of planetary cores, as well as target design in fusion energy research, where materials in the 'warm dense matter' state need to be precisely thermalized.

Micah Soto

Update 23 August 2025