Cold antimatter
In 2002 ATHENA researchers produced the first cold atoms of antihydrogen, opening the possibility of comparing antihydrogen atoms with ordinary hydrogen. This image shows the transverse density of antiproton annihilation events integrated along the z-direction of a cylindrical Penning trap: red indicates high antiproton density; blue indicates low. The red ring corresponds to the inner wall of the Penning trap, which has a radius of 1.25 cm. Image: Nature.