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Post-merger evolution of a neutron star-black hole binary with neutrino transport

Foucart, Francois and O'Connor, Evan and Roberts, Luke and Duez, Matthew D. and Haas, Roland and Kidder, Lawrence E. and Ott, Christian D. and Pfeiffer, Harald P. and Scheel, Mark A. and Szilagyi, Bela (2015) Post-merger evolution of a neutron star-black hole binary with neutrino transport. Physical Review D, 91 (12). Art. No. 124021. ISSN 1550-7998. doi:10.1103/PhysRevD.91.124021.

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We present a first simulation of the post-merger evolution of a black hole-neutron star binary in full general relativity using an energy-integrated general-relativistic truncated moment formalism for neutrino transport. We describe our implementation of the moment formalism and important tests of our code, before studying the formation phase of an accretion disk after a black hole-neutron star merger. We use as initial data an existing general-relativistic simulation of the merger of a neutron star of mass 1.4M_⊙ with a black hole of mass 7M_⊙ and dimensionless spin χBH=0.8. Comparing with a simpler leakage scheme for the treatment of the neutrinos, we find noticeable differences in the neutron-to-proton ratio in and around the disk, and in the neutrino luminosity. We find that the electron neutrino luminosity is much lower in the transport simulations, and that both the disk and the disk outflows are less neutron rich. The spatial distribution of the neutrinos is significantly affected by relativistic effects, due to large velocities and curvature in the regions of strongest emission. Over the short time scale evolved, we do not observe purely neutrino-driven outflows. However, a small amount of material (3×10^(−4)M_⊙) is ejected in the polar region during the circularization of the disk. Most of that material is ejected early in the formation of the disk, and is fairly neutron rich (electron fraction Ye∼0.15–0.25). Through r-process nucleosynthesis, that material should produce high-opacity lanthanides in the polar region, and could thus affect the light curve of radioactively powered electromagnetic transients. We also show that by the end of the simulation, while the bulk of the disk remains neutron rich (Ye∼0.15–0.2 and decreasing), its outer layers have a higher electron fraction: 10% of the remaining mass has Ye>0.3. As that material would be the first to be unbound by disk outflows on longer time scales, and as composition evolution is slower at later times, the changes in Ye experienced during the formation phase of the disk could have an impact on nucleosynthesis outputs from neutrino-driven and viscously driven outflows. Finally, we find that the effective viscosity due to momentum transport by neutrinos is unlikely to have a strong effect on the growth of the magnetorotational instability in the post-merger accretion disk.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Foucart, Francois0000-0003-4617-4738
O'Connor, Evan0000-0002-8228-796X
Roberts, Luke0000-0001-7364-7946
Duez, Matthew D.0000-0002-0050-1783
Haas, Roland0000-0003-1424-6178
Kidder, Lawrence E.0000-0001-5392-7342
Ott, Christian D.0000-0003-4993-2055
Pfeiffer, Harald P.0000-0001-9288-519X
Additional Information:© 2015 American Physical Society. Received 17 February 2015; published 11 June 2015. The authors wish to thank Brett Deaton, Rodrigo Fernandez, and Dan Kasen for useful discussions over the course of this project, and the members of the SXS Collaboration for their suggestions and support. F. F. gratefully acknowledges support from the Vincent and Beatrice Tremaine Postdoctoral Fellowship. Support for this work was provided by NASA through Einstein Postdoctoral Fellowship Grants No. PF4-150122 (F. F.) and No. PF3- 140114 (L. R.) awarded by the Chandra X-ray Center, which is operated by the Smithsonian Astrophysical Observatory for NASA under contract No. NAS8-03060; and through Hubble Fellowship Grant No. 51344.001 (E. O.) awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract No. NAS 5-26555. The authors at CITA gratefully acknowledge support from the NSERC Canada. M. D. D. acknowledges support through NSF Grant No PHY-1402916. L.K. acknowledges support from NSF Grants No. PHY- 1306125 and No. AST-1333129 at Cornell, while the authors at Caltech acknowledge support from NSF Grants No PHY-1068881, No. PHY-1404569, No. AST-1205732 and No. AST-1333520, and from NSF CAREER Award No PHY-1151197. Authors at both Cornell and Caltech also thank the Sherman Fairchild Foundation for their support. Computations were performed on the supercomputer Briarée from the Université de Montréal, and Guillimin from McGill University, both managed by Calcul Québec and Compute Canada. The operation of these supercomputers is funded by the Canada Foundation for Innovation (CFI), Ministère de l’Économie, de l'Innovation et des Exportations du Québec (MEIE), RMGA and the Fonds de recherche du Québec— Nature et Technologie (FRQ-NT). Computations were also performed on the Zwicky cluster at Caltech, supported by the Sherman Fairchild Foundation and by NSF Award No PHY- 0960291. This work also used the Extreme Science and Engineering Discovery Environment (XSEDE) through allocation No. TGPHY990007N, supported by NSF Grant No. ACI-1053575.
Group:TAPIR, Walter Burke Institute for Theoretical Physics
Funding AgencyGrant Number
Vincent and Beatrice Tremaine Postdoctoral FellowshipUNSPECIFIED
NASA Einstein FellowshipPF4-150122
NASA Einstein FellowshipPF3-140114
NASA Hubble Fellowship51344.001
Natural Sciences and Engineering Research Council of Canada (NSERC)UNSPECIFIED
Sherman Fairchild FoundationUNSPECIFIED
Canada Foundation for InnovationUNSPECIFIED
Ministère de l’Économie, de l'Innovation et des Exportations du Québec (MEIE)UNSPECIFIED
Fonds de recherche du Québec-Nature et technologies (FRQ-NT)UNSPECIFIED
NASANAS 5-26555
Issue or Number:12
Classification Code:PACS numbers: 04.25.D-, 26.30.Hj, 97.60.Jd
Record Number:CaltechAUTHORS:20150706-102844751
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:58770
Deposited On:13 Jul 2015 19:41
Last Modified:10 Nov 2021 22:10

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