Astronomy Picture of the Day . Radioactive Clouds in the Milky Way . ... Credit Copyright: NASA , Compton Gamma Ray Observatory , COMPTEL Collaboration , Explanation: When massive stars explode they create large radioactive blast clouds which expand into interstellar space. ... The map was made by a telescope onboard NASA's orbiting Compton Gamma Ray Observatory using detectors sensitive to gamma rays from the decay of radioactive aluminum. ... Publications with keywords: Milky Way . ...