The physics behind astrophysical transients

With an increased emphasis on time-domain and multi-messenger astrophysics, astrophysical transients have catapulted in importance over the past few years. Astronomers are discovering an increasingly diverse set of transient phenomena. Oftentimes, the menagerie of transients are analyzed using simplified models designed for a single transient. Using such inappropriate models often leads to incorrect interpretations of these models. This misuse often lies in a poor understanding of the basic physics powering astrophysical transients. In this paper, we review this basic physics, building up the different physical components behind transient emission toward increasingly complex models behind astrophysical phenomena. These discussions allow us to better understand the misconceptions in our current interpretations of astrophysical transients.