These relativistic jets, as they're called, are thought to contain a plasma made of electrons and their antimatter equivalent, positrons. But exactly how this stuff is made, and what effects it has, is tricky to measure from astronomical observations and computer simulations. So, CERN scientists set out to create their own versions in the lab. Using the High-Radiation to Materials (HiRadMat) facility, the team captured 300 billion protons from the Super Proton Synchrotron and blasted them onto targets made of graphite and tantalum. This sets off a cascade of particle interactions that generates enough electron-positron pairs to sustain a stable plasma state.