Physical interaction Astronomical phenomena Electromagnetism: observation using the electromagnetic spectrum black body radiation stellar radiation synchrotron radiation radio and X-ray sources inverse-Compton scattering astronomical X-ray sources acceleration of charged particles pulsars and cosmic rays absorption/scattering interstellar dust Strong and weak interaction: nucleosynthesis in stars cosmic rays supernovae primeval universe Gravity: motion of planets, satellites and binary stars, stellar structure and evolution, N-body motions in clusters of stars and galaxies, black holes, and the expanding universe.[1]