Neutron stars and black holes are often discovered when telescopes detect light produced in their vicinity. The common challenge to explain these stunning observations is understanding the behavior of plasma, the hot magnetized gas producing the emission, under conditions we cannot explore on Earth. Remarkable recent observational discoveries, including Fast Radio Bursts and silhouettes of black holes, call for breakthroughs in our understanding of the physics of plasmas around these objects. To unveil the physical mechanisms behind these observations, I developed the first-of-its-kind numerical approach for simulating black hole and neutron star environments that self-consistently account for the dynamics of charged particles and their interactions with photons. My group plans to apply these tools to build first-principles models of Fast Radio Bursts and to explain how electrons energize close to the black hole to produce the Event Horizon Telescope’s ring of light.