Violent cosmic conditions recreated in lab

Scientists have performed sophisticated experiments and computer simulations to recreate violent cosmic conditions on a small scale in the lab, in order to understand extreme events in the vast universe.

High pressure can turn a soft form of carbon —graphite, used as pencil lead — into an extremely hard form of carbon, diamond.

Scientists have predicted that the same thing could happen when a meteor hits graphite in the ground, and that these impacts might be powerful enough to produce a form of diamond, called “lonsdaleite”, that is even harder than regular diamond.

“The existence of lonsdaleite has been disputed, but we’ve now found compelling evidence for it,” said Siegfried Glenzer, from the US department of energy’s SLAC National Accelerator Laboratory.

The team heated the surface of graphite with a powerful optical laser pulse that set off a shock wave inside the sample and rapidly compressed it.

By shining bright, ultrafast X-rays from SLAC’s X-ray laser Linac Coherent Light Source (LCLS) through the sample, the researchers were able to see how the shock changed the graphite’s atomic structure.

“We saw that lonsdaleite formed for certain graphite samples within a few billionths of a second and at a pressure of about 200 gigapascals — 2 million times the atmospheric pressure at sea level,” said lead researcher Dominik Kraus from the German Helmholtz Centre Dresden-Rossendorf.

“These results strongly support the idea that violent impacts can synthesise this form of diamond, and that traces of it in the ground could help identify meteor impact sites,” Kraus said.

Another study looked at a peculiar transformation that might occur inside giant gas planets like Jupiter, whose interior is largely made of liquid hydrogen.

At high pressure and temperature, this material is believed to switch from its “normal,” electrically insulating state into a metallic, conducting one.

“It appears that as the pressure and temperature of the laser-induced shock wave rip the molecules apart, their electrons become unbound and are able to conduct electricity,” said lead author Paul Davis.