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Monte-Carlo Neutrino Transport in Neutron Star Merger Simulations

Foucart, Francois and Duez, Matthew D. and Hebert, Francois and Kidder, Lawrence E. and Pfeiffer, Harald P. and Scheel, Mark A. (2020) Monte-Carlo Neutrino Transport in Neutron Star Merger Simulations. Astrophysical Journal Letters, 902 (1). Art. No. L27. ISSN 2041-8213.

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Gravitational waves and electromagnetic signals from merging neutron star binaries provide valuable information about the the properties of dense matter, the formation of heavy elements, and high-energy astrophysics. To fully leverage observations of these systems, we need numerical simulations that provide reliable predictions for the properties of the matter unbound in these mergers. An important limitation of current simulations is the use of approximate methods for neutrino transport that do not converge to a solution of the transport equations as numerical resolution increases, and thus have errors that are impossible to quantify. Here, we report on a first simulation of a binary neutron star merger that uses Monte-Carlo techniques to directly solve the transport equations in low-density regions. In high-density regions, we use approximations inspired by implicit Monte-Carlo to greatly reduce the cost of simulations, while only introducing errors quantifiable through more expensive convergence studies. We simulate an unequal mass neutron star binary merger up to 5 ms past merger, and report on the properties of the matter and neutrino outflows. Finally, we compare our results to the output of our best approximate "M1" transport scheme, demonstrating that an M1 scheme that carefully approximates the neutrino energy spectrum only leads to ~10% uncertainty in the composition and velocity of the ejecta, and ~20% uncertainty in the ν_e and ν^(bar)_e luminosities and energies. The most significant disagreement found between M1 and Monte-Carlo results is a factor of ~2 difference in the luminosity of heavy-lepton neutrinos.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Foucart, Francois0000-0003-4617-4738
Duez, Matthew D.0000-0002-0050-1783
Kidder, Lawrence E.0000-0001-5392-7342
Pfeiffer, Harald P.0000-0001-9288-519X
Additional Information:© 2020. The American Astronomical Society. Received 2020 August 24; revised 2020 September 14; accepted 2020 September 25; published 2020 October 13. We are grateful to Sherwood Richers, Ernazar Abdikamalov, Ben Ryan, Charles Gammie, Dan Kasen, Jonah Miller, and Josh Dolence for useful discussions regarding neutrino transport and Monte-Carlo methods. We also thank Aurore Bertranhandy for her help with the NuLib library. We are grateful to the Yukawa Institute for Theoretical Physics the Center for Computational Astrophysics for hosting some of these discussions. F.F. gratefully acknowledges support from the DOE through Early Career award DE-SC0020435, from the NSF through grant PHY-1806278, and from NASA through grant 80NSSC18K0565. M.D. gratefully acknowledges support from the NSF through grant PHY-1806207. F.H. and M.S. acknowledge funding from NSF Grants PHY1708212 and PHY1708213. L.K. acknowledges support from NSF grant PHY-1606654 and PHY-1912081. F.H., L.K. and M.S. also thank the Sherman Fairchild Foundation for their support.
Group:TAPIR, Walter Burke Institute for Theoretical Physics
Funding AgencyGrant Number
Department of Energy (DOE)DE-SC0020435
Sherman Fairchild FoundationUNSPECIFIED
Subject Keywords:R-process ; Neutron stars ; Gravitational wave sources ; Computational methods ; Computational astronomy
Issue or Number:1
Classification Code:Unified Astronomy Thesaurus concepts: R-process (1324); Neutron stars (1108); Gravitational wave sources (677); Computational methods (1965); Computational astronomy (293)
Record Number:CaltechAUTHORS:20201013-114813417
Persistent URL:
Official Citation:Francois Foucart et al 2020 ApJL 902 L27
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:106023
Deposited By: George Porter
Deposited On:13 Oct 2020 20:05
Last Modified:13 Oct 2020 20:05

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