HOW TO MAKE IT

To create it, Silvera and Dias squeezed a tiny hydrogen sample at 495 gigapascal, or more than 71.7 million pounds-per- square inch - greater than the pressure at the center of the Earth.

At those extreme pressures, solid molecular hydrogen -which consists of molecules on the lattice sites of the solid - breaks down, and the tightly bound molecules dissociate to transforms into atomic hydrogen, which is a metal. conducting coils could be used to store excess energy, which could then be used whenever it is needed.

David Ceperley, a physics professor at the University of Illinois UrbanaChampaign who was not involved in the research, said the discovery, if confirmed, would end a decades-long quest to see how hydrogen can become a metal, adding to the understanding of the most common element in the universe.

To achieve this feat, Silvera and post-doctoral fellow Ranga Dias squeezed a tiny hydrogen sample at more than 71.7 million pounds per square inch (32.5 million kg per 6.5 square cm), greater than the pressure at the center of the Earth.

The scientists created this force using synthetic diamonds mounted opposite each other in a device known as a diamond anvil cell.

They treated the diamonds with a special process to keep them from cracking, a problem that has foiled prior experiments.

'This is just at the point when the diamonds are about to crack,' Ceperley said.

'That is why it's taken so long. Silvera had new ways of shaping the diamonds and polishing them so they wouldn't break.'

A key question is whether the pressurized hydrogen maintains its metallic properties at room temperature, which would make it extremely useful as a superconductor.

Both Ceperley and Silvera believe this will be the case, but it still needs to be proven.