Multi-messenger puzzles in search of the origin of Galactic cosmic rays
Cosmic rays are high-energy particles that originate from outside the solar system. The fluxes of cosmic rays cover a wide energy range from 109 eV up to 1021 eV. In comparison, energetic particles from the Sun can reach up to 1010 eV during extreme solar events. To reach higher energies than solar energetic particles, we expect the source sites of cosmic rays to be more extreme than our Sun. Supernova remnants have been the most supported candidates to be our Galaxy's main sources of cosmic rays. The direction of cosmic rays cannot be used to find out the source of Galactic cosmic rays as cosmic rays’ trajectories are deflected by magnetic fields. However, we can study the source of cosmic rays by observing neutral particles, such as gamma rays and neutrinos, as these could be produced by the interactions of cosmic rays with material around the source regions. Recently, there have been great advances in our knowledge of Galactic cosmic rays thanks to the updated measurements of all three messengers: cosmic rays, gamma rays, and neutrinos. The strength of multi-messenger observation is the requirement for these observations to be consistent with each other. I will present an overview of current high-energy astrophysical observations of our Galaxy and a glimpse into future perspectives, especially from HELIX (a balloon-borne cosmic-ray instrument) and the IceCube neutrino observatory at the South Pole.