  Observations have shown that spatially extended "TeV halos" are a common (and
potentially generic) feature surrounding young and middle-aged pulsars.
However, their morphology is not understood. They are larger than the "compact"
region where the stellar remnant dominates the properties of the interstellar
medium, but smaller than expected in models of cosmic-ray diffusion through the
standard interstellar medium. Several explanations have been proposed, but all
have shortcomings. Here, we revisit a class of models where the cosmic-ray
gradient produced by the central source induces a streaming stability that
"self-confines" the cosmic-ray population. We find that previous studies
significantly underpredicted the degree of cosmic-ray confinement and show that
corrected models can significantly inhibit cosmic-ray diffusion throughout the
TeV halo, especially when similar contributions from the coincident supernova
remnant are included.
