Strangeness-driven bulk viscosity in neutron stars: A reaction network approach

Sammanfattning

An open question in high-density physics is whether strange hyperons are present in the dense cores of neutron stars. To this end, constraining the behavior of dense nuclear matter is one of the most exciting prospects in gravitational-wave astronomy. If hyperons are present, they could give rise to bulk viscous dissipation, caused by chemical equilibration processes. Recently, the role of bulk viscous dissipation in neutron star mergers has been investigated, arising from either β-equilibration processes or the equilibration of strangeness. At the low temperatures relevant for the inspiral phase, strangeness-driven bulk viscous dissipation could become important, which could, in turn, provide means for observationally investigating the presence of hyperons.In this thesis, we develop a reaction network for numerically post-processing numerical relativity neutron star merger simulations to estimate the strangeness-driven bulk viscous dissipation in dense matter. By using an out-of-weak-equilibrium chiral mean field equation of state, we solve a system of coupled partial differential equations to numerically evolve the number densities of different species in the matter over time. We present tests of the reaction network and estimate the bulk viscous dissipation for small density oscillations, yielding good agreement with previous calculations.Using this reaction network, the next step is to provide a new estimate for strangeness-driven bulk viscous dissipation in neutron star mergers and determine its possible observational signature.