Emergence of Microphysical Bulk Viscosity in Binary Neutron Star Postmerger Dynamics

Journal Article · 16 May 2024 · The Astrophysical Journal. Letters

DOI: https://doi.org/10.3847/2041-8213/ad454f · OSTI ID:2352306

Most, Elias R. ; Haber, Alexander ; Harris, Steven P. ; Zhang, Ziyuan ; Alford, Mark G. ; Noronha, Jorge

Abstract In nuclear matter in isolated neutron stars, the flavor content (e.g., proton fraction) is subject to weak interactions, establishing flavor ( β -)equilibrium. However, there can be deviations from this equilibrium during the merger of two neutron stars. We study the resulting out-of-equilibrium dynamics during the collision by incorporating direct and modified Urca processes (in the neutrino-transparent regime) into general-relativistic hydrodynamics simulations with a simplified neutrino transport scheme. We demonstrate how weak-interaction-driven bulk viscosity in postmerger simulations can emerge and assess the bulk viscous dynamics of the resulting flow. We further place limits on the impact of the postmerger gravitational-wave strain. Our results show that weak-interaction-driven bulk viscosity can potentially lead to a phase shift of the postmerger gravitational-wave spectrum, although the effect is currently on the same level as the numerical errors of our simulation.

• Sponsoring Organization: USDOE
• Grant/Contract Number: FG02-05ER41375.; FG02-00ER41132; SC0021301; SC0023861
• OSTI ID: 2352306
• Journal Information: The Astrophysical Journal. Letters, Journal Name: The Astrophysical Journal. Letters Vol. 967 Journal Issue: 1; ISSN 2041-8205
• Publisher: American Astronomical SocietyCopyright Statement
• Country of Publication: United States
• Language: English