Evidence for protostellar jets as a population of hadronic gamma-ray sources

Abstract: Stars are born in darkness, deep within cold, dense molecular clouds where gravity drives the collapse of gas and dust, giving rise to protostars, the earliest stages of stellar evolution. Once considered purely thermal sources, these young systems are now emerging as sites of energetic non-thermal activity. While radio synchrotron jets hinted at the presence of relativistic electrons, direct confirmation of proton acceleration remained elusive. Here we report a statistically significant detection of gamma rays from a population of young stellar objects, revealing a Galactic class of Gamma-Loud Protostars. Observations point towards particle acceleration within protostellar jets, where gamma-ray emission arises from protons interacting with surrounding molecular clouds via pion decay. We find a correlation between cosmic-ray output and bolometric luminosity, suggesting that particle acceleration scales with the system's mechanical power. These findings open a new observational window into the role of non-thermal processes in protostellar evolution and suggest that gamma-ray studies of protostars can provide critical insights into accretion, ejection, and feedback in star formation. This previously overlooked emission traces the energetic feedback that young stars inject into their surroundings, shaping the conditions for subsequent star and planet formation.