Les systèmes binaires X sont des systèmes composés d'un objet compact (un trou noir ou bien une étoile à neutrons) et d'une étoile. Ces systèmes sont "transitoires", c'est-à-dire qu'ils passent la majeure partie de leur temps dans un état dit de "quiescence" où ils sont au repos et très peu brillants.

Recently completed, the Large High Altitude Air Shower Observatory (LHAASO) is the most sensitive detector exploring the sky in the ultra-high-energy (UHE, > 0.1 PeV) gamma-ray domain. It already detected about a dozen sources, whose spectra extend up to photon energies exceeding 1 PeV. Such photons are produced in interactions between protons of multi-PeV energy with ambient matter. These observations are extremely important because, in order to explain the observed spectrum of Galactic cosmic rays, astrophysical sources capable of accelerating protons beyond 1 PeV must exist.

Completed in 2021, the Large High Altitude Air Shower Observatory  (LHAASO) is the most sensitive instrument probing the sky in the ultra-high-energy (>0.1 PeV) gamma-ray domain. It already detected about a dozen sources whose spectra extend to PeV energies. Such energetic photons are produced in interactions of multi-PeV cosmic rays with ambient matter. LHAASO sources have been tentatively associated with pulsar wind nebulae, young massive stellar clusters and supernova remnants.