Constraints from GW170817 on the bulk viscosity of neutron star matter and the r-mode instability

Understand

We perform a systematic study of the dependence of the r-mode phenomenology in normal fluid pulsar neutron stars on the symmetry energy slope parameter $L$.

• An essential ingredient in this study is the bulk viscosity, which is evaluated consistently for several equations of state corresponding to different values of the slope parameter $L$.
• Direct Urca processes, which are allowed from a critical $L$-value onwards, enhance the bulk viscosity and have large influence on the $r$-mode features, such as the instability boundary and spin-down properties of newborn neutron stars.
• The magnitude of the changes in the $r$-mode properties induced by the direct Urca processes are driven by the $L$-value of the equation of state and the mass of the pulsar.