Dynamical mass ejection from black hole-neutron star binaries

Koutarou Kyutoku, Kunihito Ioka, Hirotada Okawa, Masaru Shibata, and Keisuke Taniguchi
Phys. Rev. D 92, 044028 – Published 18 August 2015

Abstract

We investigate properties of material ejected dynamically in the merger of black hole-neutron star binaries by numerical-relativity simulations. We systematically study the dependence of ejecta properties on the mass ratio of the binary, spin of the black hole, and equation of state of the neutron-star matter. Dynamical mass ejection is driven primarily by tidal torque, and the ejecta is much more anisotropic than that from binary neutron star mergers. In particular, the dynamical ejecta is concentrated around the orbital plane with a half opening angle of 10°–20° and often sweeps out only a half of the plane. The ejecta mass can be as large as 0.1M, and the velocity is subrelativistic with 0.20.3c for typical cases. The ratio of the ejecta mass to the bound mass (disk and fallback components) is larger, and the ejecta velocity is larger, for larger values of the binary mass ratio, i.e., for larger values of the black-hole mass. The remnant black hole-disk system receives a kick velocity of O(100)kms1 due to the ejecta linear momentum, and this easily dominates the kick velocity due to gravitational radiation. Structures of postmerger material, velocity distribution of the dynamical ejecta, fallback rates, and gravitational waves are also investigated. We also discuss the effect of ejecta anisotropy on electromagnetic counterparts, specifically a macronova/kilonova and synchrotron radio emission, developing analytic models.

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  • Received 18 February 2015

DOI:https://doi.org/10.1103/PhysRevD.92.044028

© 2015 American Physical Society

Authors & Affiliations

Koutarou Kyutoku1,2, Kunihito Ioka3,4, Hirotada Okawa5,6, Masaru Shibata5, and Keisuke Taniguchi7,8

  • 1Department of Physics, University of Wisconsin-Milwaukee, P.O. Box 413, Milwaukee, Wisconsin 53201, USA
  • 2Interdisciplinary Theoretical Science (iTHES) Research Group, RIKEN, Wako, Saitama 351-0198, Japan
  • 3Theory Center, Institute of Particles and Nuclear Studies, KEK, Tsukuba 305-0801, Japan
  • 4Department of Particle and Nuclear Physics, the Graduate University for Advanced Studies (Sokendai), Tsukuba 305-0801, Japan
  • 5Yukawa Institute for Theoretical Physics, Kyoto University, Kyoto 606-8502, Japan
  • 6Advanced Research Institute for Science and Engineering, Waseda University, Okubo 3-4-1, Shinjuku, Tokyo 169-8555, Japan
  • 7Graduate School of Arts and Sciences, University of Tokyo, Komaba, Meguro, Tokyo 153-8902, Japan
  • 8Department of Physics, University of the Ryukyus, Nishihara, Okinawa 903-0213, Japan

See Also

Anisotropic mass ejection from black hole-neutron star binaries: Diversity of electromagnetic counterparts

Koutarou Kyutoku, Kunihito Ioka, and Masaru Shibata
Phys. Rev. D 88, 041503(R) (2013)

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Vol. 92, Iss. 4 — 15 August 2015

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