Laser Test Keeps Gold Solid at 19,000K, Challenging Thermodynamic Limits

Gold can withstand far higher temperatures than previously thought, according to a study published in Nature. A team led by Thomas White at the University of Nevada, Reno, used an optical laser to blast 50-nanometre-thick gold films for 45 femtoseconds, momentarily raising the metal’s temperature to about 19,000 kelvin—around 14 times its 1,337 K melting point—without melting it. Researchers then fired the Linac Coherent Light Source X-ray laser at SLAC National Accelerator Laboratory to gauge the sample’s temperature from shifts in the reflected photons, giving a direct reading during the few-picosecond window before the gold vaporised. The measurement eclipses the long-accepted ‘entropy catastrophe’ threshold, which posited that no solid could exceed roughly three times its melting point without violating thermodynamic principles. The work reopens fundamental questions about phase transitions and may aid modelling of warm dense matter found in planetary cores, fusion experiments and spacecraft heat shields. The team is already applying the technique to other metals to probe whether an upper limit to superheating exists.