LHAASO and the galactic cosmic rays

A schematic view of the air shower observed by LHAASO array, and the 12 sources detected by LHAASO using 11 months data of half array

Cosmic rays (CRs) are relativistic charged particles in the interstellar medium (ISM). They are mainly protons (hydrogen nuclei) with about 10% fraction of helium nuclei and smaller abundances of heavier elements. CR is an important component in ISM. In our Galaxy, the energy density of CRs is similar to that of the magnetic fields and interstellar radiation fields (ISRF). CRs also determine the ionization rate and heating of gas in the dense core of molecular clouds, thus play a leading role in the astro-chemistry processes therein and control the star-forming processes. More than a century has passed since Hess discovered the extra-terrestrial origin of CRs (in 1912), yet the origin of CRs still remains as a mystery.