Resumen: Neutron star (NS) mergers are among the most promising multimessenger sources in the Universe, as demonstrated by the coincident detection of gravitational waves (GWs) and multiwavelength electromagnetic (EM) radiation with the GW170817 event. Moreover, they have also been proposed as potential sources of ultra-high-energy cosmic rays and high-energy neutrinos. One of the most studied observable phenomena associated with NS mergers are the so-called short-duration gamma-ray bursts (sGRBs), which are thought to originate from a relativistic jet launched by the merger remnant. However, there are still uncertainties about the exact nature of such a remnant: it may be a promptly formed black hole (BH), a hypermassive NS that collapses to a BH on timescales of ~100 ms, or even a stable NS. In this talk, I will talk about the theoretical modeling of NS mergers through GRMHD simulations, what these studies teach us about the properties of matter at extreme densities, and how we can predict potential multimessenger signatures from these phenomena.