I am a theoretical astrophysicist. I apply physical laws to understand astronomical phenomena. My primary research interest is high-energy astrophysics, which studies, among other things, black holes of various scales, neutron stars of various species, and the intense "jets" they launch. For many years, I have been studying the physical mechanisms of Gamma-ray bursts (GRBs), the most luminous explosions in the universe. See my book on this topic. Recently, I am spending most of my research time studying multi-messenger (gravitational waves and electromagnetic counterparts, high energy neutrinos) astrophysics and a type of mysterious bursts known as fast radio bursts (FRBs).