They move steadily around the nucleus and stay out of each other's way. But new research reveals that if the pressure is really extreme, like double that found at the center of the Earth, the innermost electrons of an atom change their behavior.

The international team of researchers that observed this anomalous, unexpected phenomenon managed to put a metal called osmium, which is almost the densest of all known metals and almost as incompressible as diamond, under static pressure of over 770 gigapascals. That's more than twice as high as the pressure at the center of the Earth and 7.7 million times higher than the mean atmospheric pressure at the sea level.

The scientists were able to do this thanks to a device called a diamond anvil cell, which can put sub-millimeter-sized materials under pressure comparable to that which creates diamonds. The portion of the research team from Bayreuth University in Germany developed synthetic diamonds that could fit between two ordinary diamonds and on each side of the osmium crystal. These synthetic diamonds reduced the area in which the osmium could fit, thereby increasing the pressure to new extremes.