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Bearing down on hydrogen

Shockwaves are used to turn deuterium into a liquid metal. [Also see Report by Knudson et al.] Under high pressure, electrons can be squeezed out of the covalent bond that holds the hydrogen molecule together. Under these conditions, condensed hydrogen can become metallic, but the pressures required can be obtained only through the gravitational field of gas giant planets, or fleetingly in shock waves. On page 1455 of this issue, Knudson et al. (1) report experiments using the Z machine at Sandia National Laboratories that uses an aluminum plate propelled by giant capacitors to generate concentrated shock waves in a tiny sample (2). They observe metallic liquid hydrogen at pressures around 300 GPa and temperatures between 1000 and 2000 K created for a tenth of a microsecond. By shock wave standards, that is remarkably cold and slow.