Scientists heat gold to 19,000 K without melting—upend long-held physics

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Scientists have managed to heat a tiny sheet of gold to a staggering 19,000 kelvins (18,727°C)—hotter than the surface of the sun—without it melting. 

The experiment, conducted with an ultra-fast laser, has shattered long-standing theories about how hot a solid can get before it falls apart.

Gold usually melts at about 1,300 kelvins (1,027°C), but in this experiment, researchers from the University of Nevada, Reno and SLAC National Accelerator Laboratory blasted a nanometres-thin gold sample with a laser for just 45 femtoseconds—a period so short that the atoms didn't have time to move or expand. 

This prevented the material from melting, despite the extreme heat.

"This was extremely surprising," said Thomas White of the University of Nevada, Reno. "We were totally shocked when we saw how hot it actually got," he told Scientific American.

The finding challenges the long-held idea of an "entropy catastrophe"—a predicted point where the disorder in solid gold should exceed that of liquid gold, violating the laws of thermodynamics. But that didn't happen. 

Instead, the gold stayed solid, showing that materials can briefly survive at temperatures previously thought impossible for solids.

To confirm just how hot the gold got, the team used the Linac Coherent Light Source at SLAC—the world's most powerful x-ray laser. This three-kilometre-long machine fired a trillion x-ray photons at the superheated gold. 

The way the x-rays bounced off the atoms allowed scientists to precisely measure their temperature, marking a breakthrough in how we measure extreme heat.

"The biggest lasting contribution is going to be that we now have a method to really accurately measure these temperatures," Bob Nagler, a staff scientist at SLAC, told Scientific American.

While some experts, like Sheng-Nian Luo from Southwest Jiaotong University in China, caution that these results may not apply to solids under normal conditions, the study team believes they've entered a "genuinely new regime" in high-temperature physics.

The team is now using this new laser-based thermometer to study other materials, including iron heated to simulate the center of Earth, where temperatures reach over 6,000 kelvins (5,727°C). 

Their method may help scientists better understand how planets and stars behave deep inside—regions that, until now, have been nearly impossible to probe.

"These questions are super important if you want to model the Earth," Nagler said.