Hunting for cosmic ray accelerators: insights from gamma-ray observations

Cosmic ray (CR) is one of the most important components in the interstellar medium (ISM) and the origin of CRs remains as a mystery.  The diffusion of CRs in turbulent magnetic fields erases the information on the distribution of CR accelerators to a large extent. In this regard, gamma-rays, the secondary products of interactions of CRs with gas and photons in the ISM, provide us more information about the origin of CRs. More specifically,  the gamma-ray emissions associated with gas, can be used to study the distribution of CRs throughout the Galaxy; the discrete gamma-ray sources can elucidate the locations of individual CR accelerators. In this talk I will review the recent advances of the gamma-ray astronomy and focus on their implications to the origin of CRs.