1.7 General relativistic study of late inspiral and merger

As illustrated above, general relativistic effects (the general relativistic attractive force between two bodies and resulting presence of the ISCO, spin-orbit coupling effect, and the general relativistic self-gravity in the NS) play a crucial role in the dynamics of a close binary system of a BH and a NS. Up to merger, the dynamics are primarily determined by the strong general relativistic gravity, and thus, the orbital evolution in a close binary, the merger and tidal disruption processes, the criterion of tidal disruption, and the evolution of the tidally-disrupted NS material depend strongly on general relativistic effects. Numerical computation in a fully general relativistic framework is obviously required for accurately and quantitatively understanding the nature of orbital evolution and the merger of BH-NS binaries; although non–general-relativistic works have provided a qualitative insight for these systems. Fortunately, the simulation in full general relativity is not a difficult task any longer, as reviewed in this paper. Now there is no reason to employ approximate frameworks for the study of this system.

Since 2005, which was the break-through year in the field of numerical relativity, the simulation of binaries composed of BHs has been feasible. Soon after the first success for the simulation of BH-BH binaries [162Jump To The Next Citation Point], work on the merger of BH-NS binaries was published [202Jump To The Next Citation Point, 203Jump To The Next Citation Point, 197Jump To The Next Citation Point, 62Jump To The Next Citation Point, 58Jump To The Next Citation Point, 63Jump To The Next Citation Point, 194Jump To The Next Citation Point, 57Jump To The Next Citation Point, 107Jump To The Next Citation Point, 108Jump To The Next Citation Point, 41Jump To The Next Citation Point, 74Jump To The Next Citation Point, 154Jump To The Next Citation Point, 109Jump To The Next Citation Point]. Shibata and his collaborators (hereafter the Kyoto/Tokyo (KT) group) performed a fully general relativistic simulation for a BH-NS binary merger for the first time, extending their earlier works for NS-NS binaries [193, 200, 201, 198, 199Jump To The Next Citation Point, 196]. Soon after the success of the KT group, the University of Illinois at Urbana-Champaign (UIUC) and Caltech/Cornell/CITA/Washington State University (CCCW) groups also performed simulations for BH-NS binary merger. The UIUC group extended their earlier work on NS-NS binaries [59], and the CCCW group extended their work for BH-BH binaries [30Jump To The Next Citation Point, 31Jump To The Next Citation Point, 181Jump To The Next Citation Point] incorporating the hydrodynamics equation solvers [57Jump To The Next Citation Point]. Subsequently, several scientific results have been derived recently by these groups. In addition, in 2010, the Louisiana State University/Brigham Young University/Perimeter Institute/Long Island University/Indiana University (LBPLI) and Albert Einstein Institute (AEI) groups published their first results for the BH-NS binary merger [41Jump To The Next Citation Point, 154Jump To The Next Citation Point]. All these groups will report with more sophisticated physics incorporating nuclear-theory-based EOS, microphysical processes, and magnetic-field effects in the near future. Thus, in the following sections, we focus only on reviewing the current status of the general relativistic studies (see also [56] for a review of the latest status of this field in 2010).


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