Scientists have found a way to "see" inside deuterons, the simplest atomic nuclei, to better understand the "glue" that holds the building blocks of matter together. The new results come from collisions of photons (particles of light) with deuterons, which are made of just one proton bound to one neutron. In these collisions, the photons act like an X-ray beam to provide the first glimpse of how particles called gluons are arranged within the deuteron. These collisions can also break the deuteron apart, giving insights into what holds the proton and neutron together.