Atom's core gets pear-shaped

Atomic nuclei come in many shapes and sizes, and scientists have now obtained precise measurements of an elusive form: pear-shaped. Studying these exotic nuclei, which are described in the May 9 Nature, could allow physicists to better understand subatomic structure and to find new particles and forces.

“It’s a beautiful, clear-cut result of a very careful experiment,” says Christopher Lister, a physicist at the University of Massachusetts in Lowell.

Diagrams in middle school textbooks depict atomic nuclei as spherical, but the real story is a lot more complex. Protons and neutrons are jam-packed into a space just 10^-15 meters wide, held together by a crushing force that dwarfs that of gravity. At the same time, the subatomic particles constantly move, shifting around and sometimes warping the nucleus into the shape of a football or even a flattened disk.