Abstract
General-relativistic simulations of binary neutron star (NS) mergers with viscosity reveal a new outflow mechanism operating in unequal mass binaries on dynamical timescales and enabled by turbulent viscosity. These "viscous-dynamical" ejecta are launched during the merger due to the thermalization of mass exchange streams between the secondary and the primary NS. They are characterized by asymptotic velocities extending up to ∼0.8c, and have masses that depend on the efficiency of the viscous mechanism. Depending on the unknown strength of the effective viscosity arising from magnetohydrodynamic instabilities operating during the merger, the overall mass of the dynamical ejecta could be enhanced by a factor of a few and the mass of the fast tail of the ejecta, having asymptotic velocities ≥0.6c, by up to four orders of magnitude. The radioactive decay of the expanding viscous-dynamical ejecta could produce bright kilonova transients with signatures of free neutron decay in the first hour, and enhanced near-infrared flux on a timescale of a few days. The synchrotron remnant produced by the interaction between the ejecta and the interstellar medium could also be significantly enhanced by viscosity. Such a remnant could be detected in the case of GW170817 as a rebrightening of the radio signal in the next months to years.
Original language | English |
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Article number | L35 |
Journal | Astrophysical Journal Letters |
Volume | 869 |
Issue number | 2 |
DOIs | |
State | Published - Dec 20 2018 |
Externally published | Yes |
Funding
It is a pleasure to acknowledge A.\uF0A0Burrows for the many stimulating discussions, and B.\uF0A0Metzger for comments on an earlier draft of the manuscript. D.R. gratefully acknowledges support from a Frank and Peggy Taplin Membership at the Institute for Advanced Study and the Max-Planck/Princeton Center (MPPC) for Plasma Physics (NSF PHY-1523261). A.P. acknowledges support from the INFN initiative \u201CHigh Performance data Network\u201D funded by CIPE. D.R. and A.P. acknowledge support from the Institute for Nuclear Theory (17-2b program) and from the Theory Alliance-Facility for Rare Isotope Beams (Topical Program: FRIB and the GW170817 kilonova). A.P. thanks the Institute for Advanced Study for its hospitality and support. S.B. acknowledge support by the EU H2020 under ERC Starting grant No.\uF0A0BinGraSp-714626. S.A.F. acknowledges support from the United States Department of Energy through the Computational Science Graduate Fellowship, grant No. DE-SC0019323. L.F.R. acknowledges support from U.S. Department of Energy through the award number DE-SC0017955. The simulations were performed on BlueWaters, Bridges, Comet, and Stampede, and were enabled by the NSF PRAC program (ACI-1440083 and AWD-1811236) and the NSF XSEDE program (TG-PHY160025). The analysis employed computational resources provided by both the TIGRESS high performance computer center at Princeton University, which is jointly supported by the Princeton Institute for Computational Science and Engineering (PICSciE) and the Princeton University Office of Information Technology, and the Institute for Cyber-Enabled Research, which is supported by Michigan State University.
Keywords
- hydrodynamics
- stars: neutron