Ab-initio Simulations of Cosmic Ray Escape from Their Sources*

We explore the escape of energetic cosmic rays (CRs) from their sources via hybrid (kinetic protons-fluid electrons) plasma simulations. For the first time, we self-consistently find that the excitation of streaming instabilities leads to enhanced CR diffusivity and in turn to a large pressure gradient that causes the formation of expanding bubbles of gas and self-generated magnetic fields. This phenomenon is general and is expected to occur around any sufficiently powerful CR source in the Galaxy. Our results provide a theoretical framework for explaining recent observations of gamma-ray haloes around supernova remnants, stellar clusters and pulsar wind nebulae, which are interpreted as regions where the diffusion coefficient is 10-100 times smaller than the typical Galactic one. Finally, we outline the potential role of such regions for the feedback that CRs may exert on star formation.