When some stars die, they can create jets moving almost at the speed of light. These jets probe extreme conditions near black holes and neutron stars and can even be seen from the farthest parts of the universe. This project will use sensitive radio telescopes to study how these jets form, what they are made of, and how they are shaped. This study will address open questions about how these dramatic cosmic explosions work. This research program also will provide research and training opportunities for undergraduate students at the University of Utah. The program will communicate results to the public via outreach efforts to improve scientific literacy. This project will advance our understanding of transient relativistic jets launched during the explosive deaths of stars. The investigators will combine new radio and millimeter photometry, polarimetry, and astrometry with multi-wavelength (optical, ultraviolet, X-ray) data to characterize the structure and magnetization of jets in gamma-ray bursts, tidal disruption events, and compact binary mergers. By applying analytical models and leveraging existing numerical simulations, the investigators will constrain key jet properties such as energy, opening angle, and magnetic structure, testing the "universal jet structure" hypothesis across diverse transients. The project will also probe the physics of jet launching and acceleration by connecting observed jet properties to central engine models (black holes or magnetars). Much o