Dynamical ejecta from precessing neutron star-black hole mergers with a hot, nuclear-theory based equation of state

Creators: Foucart, F.; Desai, D.; Brege, W.; Duez, M. D.; Kasen, D.; Hemberger, D. A.; Kidder, L. E.; Pfeiffer, H. P.; Scheel, M. A.

Abstract

Neutron star-black hole binaries are among the strongest sources of gravitational waves detectable by current observatories. They can also power bright electromagnetic signals (gamma-ray bursts, kilonovae), and may be a significant source of production of r-process nuclei. A misalignment of the black hole spin with respect to the orbital angular momentum leads to precession of that spin and of the orbital plane, and has a significant effect on the properties of the post-merger remnant and of the material ejected by the merger. We present a first set of simulations of precessing neutron star-black hole mergers using a hot, composition dependent, nuclear-theory based equation of state (DD2). We show that the mass of the remnant and of the dynamical ejecta are broadly consistent with the result of simulations using simpler equations of state, while differences arise when considering the dynamics of the merger and the velocity of the ejecta. We show that the latter can easily be understood from assumptions about the composition of low-density, cold material in the different equations of state, and propose an updated estimate for the ejecta velocity which takes those effects into account. We also present an updated mesh-refinement algorithm which allows us to improve the numerical resolution used to evolve neutron star-black hole mergers.

Additional Information

© 2017 IOP Publishing Ltd. Received 11 November 2016, revised 28 December 2016; Accepted for publication 6 January 2017; Published 20 January 2017. The authors thank Jennifer Barnes, Rodrigo Fernandez, Brian Metzger, Eliot Quataert, Sasha Tchekhovskoy, and the members of the SxS collaboration for helpful discussions over the course of this project. We also thank Francesco Pannarale for providing information about the predicted properties of the final black holes, listed in table 2. Support for this work was provided by NASA through Einstein Postdoctoral Fellowship grant numbered PF4-150122 (FF) awarded by the Chandra X-ray Center, which is operated by the Smithsonian Astrophysical Observatory for NASA under contract NAS8-03060. DD gratefully acknowledges support from the UC Berkeley-Rose Hills Foundation Summer Undergraduate Research Fellowship. DK is supported in part by a Department of Energy Office of Nuclear Physics Early Career Award, and by the Director, Office of Energy Research, Office of High Energy and Nuclear Physics, Divisions of Nuclear Physics, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. HP gratefully acknowledges support from the NSERC Canada. MD acknowledges support through NSF Grant PHY-1402916. LK acknowledges support from NSF grants PHY-1306125 and AST-1333129 at Cornell, while the authors at Caltech acknowledge support from NSF Grants PHY-1404569, AST-1333520, NSF-1440083, and NSF CAREER Award 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, managed by Calcul Québec and Compute Canada. The operation of these supercomputers is funded by the Canada Foundation for Innovation (CFI), NanoQuébec, 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 PHY-0960291.

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