Cosmic-ray generated bubbles around their sources

ABSTRACT Cosmic rays (CRs) are thought to escape their sources streaming along the local magnetic field lines. We show that this phenomenon generally leads excitation of both resonant and non-resonant instabilities. The self-generated fluctuations induce particle diffusion in extended regions around source, so CRs build up a large pressure gradient. By means two-dimensional (2D) three-dimensional (3D) hybrid particle-in-cell simulations, we such gradient excavates cavity source formation cosmic ray dominated bubble, inside which diffusivity is strongly suppressed. Based on trends extracted from self-consistent estimate that, absence severe damping fields, bubble should keep expanding until balance with surrounding medium reached, corresponding radius ∼10–50 pc. implications these low for Galactic discussed. Special care devoted estimating coefficient grammage might accumulate bubbles before moving into interstellar medium. results 3D general considerations morphology γ-ray synchrotron emission also outlined.