Speaker
Description
Binary neutron star (BNS) mergers are among the most promising multimessenger sources, providing simultaneous insights into strong-field gravity, dense nuclear matter, heavy-element nucleosynthesis, and transient electromagnetic phenomena. Understanding how intrinsic neutron-star properties influence merger outcomes is essential for interpreting current and future observations. In this work, we present a review of recent high-resolution general-relativistic radiation magnetohydrodynamic simulations designed to investigate the impact of neutron-star spin on post-merger evolution and associated observables. Equal-mass BNS systems consisting of 1.35 M☉ neutron stars were examined for both nonspinning and aligned-spin configurations. The simulations incorporated realistic microphysics, including neutrino transport, magnetic-field evolution, and a relativistic mean-field equation of state, while following the merger evolution up to approximately 100 ms after coalescence. The results indicate that neutron-star spin can significantly influence remnant properties and electromagnetic counterparts in the simulated configurations. The nonspinning configuration undergoes a more violent collision, producing larger quantities of faster and more neutron-rich ejecta, stronger late-time magnetic-field amplification, and comparatively brighter kilonova emission in the modeled scenarios. In contrast, the spinning configuration forms a more massive accretion disk owing to enhanced angular momentum support and exhibits comparatively higher electron fractions in the ejecta. Nucleosynthesis calculations confirm robust production of heavy elements through the rapid neutron-capture process in both scenarios, although variations in ejecta composition lead to differences in lanthanide abundances and kilonova color evolution. Gravitational-wave analysis reveals only modest spin-dependent shifts in post-merger frequencies, with the reported differences remaining comparable to numerical uncertainties. Electromagnetic counterparts may therefore provide complementary information for constraining spin-related effects in BNS mergers. Furthermore, viewing-angle-dependent kilonova emission highlights the importance of incorporating ejecta geometry and composition into observational models.
These findings emphasize that neutron-star spin is an important factor influencing the multimessenger outcomes of BNS mergers and underscore the need for increasingly realistic simulations to support the interpretation of observations from next-generation gravitational-wave detectors and wide-field electromagnetic surveys.