Neutron star mergers will provide a unique opporunity to gather observational information, especially via gravitational waves, about nuclear matter at high density and moderate temperature. Numerical simulations of mergers are an essential tool for exploiting this opportunity. However, up to now such simulations have generally not included the effects of transport or dissipation, and have focused on measuring the equation of state. To evaluate the likely importance of transport and dissipation, we obtained estimates of the equilibration times associated with thermal diffusion, shear viscosity, and bulk viscosity. We find that thermal diffusion and shear viscosity could play a significant role in mergers if neutrinos are trapped and there are gradients on a short distance scale of order 0.1 km. We find that bulk viscosity will be important if direct Urca processes remain suppressed. We conclude that some transport properties will play an important role in the merger, and should be included in future merger simulations. This opens up the possibility that observations of mergers could provide information about dense matter that goes beyond the equation of state, maybe even telling us about the presence of exotic phases.

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