Isospin Equilibration in Neutron Star Mergers

Abstract

We analyze the isospin equilibration properties of neutrinoless nuclear ($npe$) matter in the temperature and density range that is relevant to neutron star mergers. Our analysis incorporates neutrino-transparency corrections to the isospin (``beta'') equilibrium condition which become noticeable at $T\gtrsim 1$MeV. We find that the isospin relaxation rate rises rapidly as temperature rises, and at $T\approx 5$MeV it is comparable to the timescale of the density oscillations that occur immediately after the merger. This produces a resonant peak in the bulk viscosity at $T\approx 5$MeV, which causes density oscillations to be damped on the timescale of the merger. Our calculations suggest that isospin relaxation dynamics may also be relevant when neutrinos are treated more accurately via neutrino transport schemes.

12 pages, 5 figures v2: minor changes in wording, no changes to conclusions or results of v1, version published in PRC

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• Estimate for the bulk viscosity of strongly coupled quark matter using perturbative QCD and holography
• Frozen and $\beta$-equilibrated $f$ and $p$ modes of cold neutron stars: nuclear metamodel predictions
• Nonparametric extensions of nuclear equations of state: probing the breakdown scale of relativistic mean-field theory
• Effect of Magnetic Fields on Urca Rates in Neutron Star Mergers
• Suppression of composition $g$-modes in chemically-equilibrating warm neutron stars
• Burgers equation for the bulk viscous pressure of quark matter
• Toward a Unified Understanding of the Dense Matter Equation of State
• Thermal and Magnetic effects on Bulk Viscosity in Binary Neutron Star Mergers