For years, physicists have wondered whether one unstable form of copper might act like a traffic jam inside some of the most violent explosions in the universe. That question matters because those explosions, called Type-I X-ray bursts, are part of the cosmic machinery that helps build heavier elements. Hydrogen and helium dominated the early universe. Much of what came later, including the oxygen in the air and the iron deep inside Earth, had to be forged in stars and stellar blasts. Now, a team led by Mississippi State physicist Jaspreet Randhawa has directly measured a key nuclear reaction tied to that process. The result suggests the suspected slowdown is much weaker than scientists feared. Therefore, heavier elements have a clearer path to form during explosive bursts on neutron stars. “The universe began almost entirely with hydrogen and helium,” Randhawa said. “Every heavier element, from the oxygen we breathe to the iron in Earth’s core, was forged later in stars and stellar explosions. By identifying how stellar explosions build heavier elements, scientists gain a clearer picture …