Gravitational Waveforms

The gravitational wavetrain from a compact binary system may be separated into three qualitatively different phases: the inspiral, merger, and ringdown. During the inspiral phase, which takes up most of the binary's lifetime, gravity wave emission gradually reduces the binary separation. The merger phase of the gravitational wavetrain is characterized by tidal disruption of the neutron star. Finally, ringdown radiation is emitted as the distorted black hole settles down to Kerr-like equilibrium (Note: Only in the case of a vacuum spacetime does the spinning BH obey the exact Kerr solution. The BHs formed here are surrounded by gaseous disks with small, but nonnegligible, rest mass). The h_× polarization mode of the gravitational wave is shown below.

h_× Polarization (Lower Hemisphere)

Here, we have a black hole and a magnetized neutron star in a binary, with the neutron star undergoing tidal disruption due to the black hole. Shown below is h_× in the lower hemisphere. Both cases have mass ratio $q=3:1$ and BH spin 0.75. Case 1 has an irrotational NS, while case 2 has a NS with spin 0.23 (Case C in this paper). Waveforms are plotted in the region of $r/M \geq 32$. The evolution is followed through a chirp up to the wave cut-off following tidal disruption. The matter and magnetic field are evolved by solving the relativistic MHD equations and the gravitational field is evolved by solving the Einstein field equations via the BSSN formalism.

Case 1: NS Spin 0	Case 2: NS Spin 0.23
Fig. 1-1: t/M = 649	Fig. 2-1: t/M = 1366
Fig. 1-2: t/M = 737	Fig. 2-2: t/M = 1457
Fig. 1-3: t/M = 828	Fig. 2-3: t/M = 1548
Fig. 1-4: t/M = 919	Fig. 2-4: t/M = 1639
Fig. 1-5: t/M = 1010	Fig. 2-5: t/M = 1730
Fig. 1-6: t/M = 1101	Fig. 2-6: t/M = 1821
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