The physics of pulsar halos: Research progress and prospect

Diffusive TeV gamma-ray emissions have been recently discovered extending beyond the pulsar wind nebulae of a few middle-aged pulsars, implying that energetic electron/positron pairs are escaping from and radiating in ambient interstellar medium. It has suggested these extended constitute distinct class nonthermal sources, termed "pulsar halos". In this article, I will review research progress on halos discuss our current understanding their physics, including multiwavelength observations, different theoretical models, as well implications for origin cosmic-ray positron excess Galactic diffuse emission.