Binary neutron star mergers

Binary neutron star (BNS) mergers are among the most energetic events in the universe, producing gravitational waves detectable by LIGO/Virgo, short gamma-ray bursts, kilonovae powered by r-process nucleosynthesis, and a variety of electromagnetic counterparts across the spectrum. The landmark detection of GW170817 and its electromagnetic counterparts opened the era of multimessenger astronomy with neutron stars.

Understanding the physics of these mergers, from the inspiral dynamics to the post-merger remnant and the launching of relativistic jets, requires sophisticated numerical simulations that combine general relativity, magnetohydrodynamics, and nuclear physics.

Toroidal magnetic field structure in a BNS post-merger remnant. From (Gutiérrez et al., 2025).

In (Gutiérrez et al., 2025) and (Cook et al., 2025), we performed a systematic study of how different magnetic field configurations evolve in the post-merger remnant and surrounding accretion disk. By performing high-resolution GRMHD simulations with various initial field geometries, we identified how the magnetic field topology affects the disk structure and outflows.
In (Gutiérrez et al., 2025), I investigated a novel electromagnetic precursor to the main kilonova emission: the cocoon shock breakout signal. I developed a theoretical framework to predict the properties of this early-time emission, which could serve as an important target for follow-up observations of future BNS merger events.

Schematic diagram of the cocoon shock breakout emission from a BNS merger. From (Gutiérrez et al., 2025).