Relativistic Matter in Neutron Star Mergers and Big Bang Nucleosynthesis

The interplay of relativistic astrophysics and nuclear physics is an active frontier in the unraveling of the properties of matter. The physics of extreme gravity is also one of the most challenging to understand due to its inaccessibility from terrestrial laboratories. In this dissertation I discuss my work on understanding the interactions of relativistic fluids and nuclear matter in two extreme environments: 1) the merger of two neutron stars and the subsequent collapse of the postmerger hypermassive neutron star to a black hole; and 2) the first few moments of cosmic expansion in the big bang. In the first part I will describe my investigation of the role of the high-density nuclear equation of state in the emergent gravitational radiation from the collapse to a black hole during neutron star mergers. In the second environment I will discuss the work I completed to formulate a solution to the multicomponent multi-dimensional relativistic thermalization to directly obtain baryon distribution during primordial nucleosynthesis.