Erlangen 2026 – scientific programme

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GR: Fachverband Gravitation, Relativistische Astrophysik und Kosmologie

GR 11: Numerical Relativity II

GR 11.3: Talk

Thursday, March 19, 2026, 11:45–12:00, KH 01.016

Gravitational Scattering of two Neutron Stars — •Joan Fontbuté — Friedrich-Schiller Universität, Jena, Germany

In this talk I'm going to present the first numerical relativity simulations of gravitational scattering between neutron stars and the first comparison of such simulations with analytical predictions as well as the black hole case. Constraint-satisfying initial data for two equal-mass non-spinning sequences are constructed at fixed energy and various initial angular momenta for two Equations of State. Our results probe extreme strong-field regimes up to the threshold of dynamical capture, revealing both agreement and significant tidal discrepancies with effective-one-body and post-Minkowskian predictions to the scattering angle. Together with these results obtained with the BAM code, I'm also going to present an extension to more realistic scenarios containing magnetic fields, M1 neutrino transport and a better atmosphere treatment with the GR-Athena++ code, where we also study in detail other properties of such events like the final spins, magnetic field properties and mass ejecta. The matter ejected is found to be crucial to explain the decrease in the binding energy that eventually makes the system become bound.

Keywords: Numerical Relativity; Neutron Stars; Scattering; Tidal interactions; Magnetic fields