With Dr. Roger Romani (Stanford University):NASA's Fermi Gamma-ray Space Telescope has revealed a violent high-energy universe full of stellar explosions, black hole jets, and pulsing stars. These cosmic objects are often faint when observed with visible light, but glow bright with gamma rays. Dr. Romani describes the quest to discover the true nature of the most puzzling of these gamma-ray sources. Several turn out to be a kind of bizarre star corpse called a 'black widow'...