Unequal Mass BHBH Evolution

Introduction
Evolution of BHBH merger
Evolution of Gravitational Radiation Profile
Final Black Hole Parameters


Introduction


Fig. 1-1 Initial Configuration of Binary

Evolution is performed with the BSSN scheme on an AMR grid with 10 levels of refinement. The outer boundary of our grid is 512M and the mesh spacing ranges from &DeltaXmax = 10.24M in the outermost level to &DeltaXmin = 0.01M in the innermost level. In this simulation, the initial coordinate radius of the binary orbit is D0/M = 7.07. Here M is the total initial ADM mass. The black hole interiors, bounded by their apparent horizons, are denoted by black spheres. Their motion is shown in the orbital plane. The evolution is performed with the BSSN scheme utilizing "moving puncture" gauge conditions. (Note: The circle in the lower right-hand corner of the above figure is a clock.)


Evolution

The binary makes approximately three orbits prior to merging at t ≈ 270M. As the inital binary merges, we see the development of a common horizon which oscillates until settling down at t ≈ 300M. After the merger, the final BH has a recoil velocity of 174 km/s. The simulation continues until t = 440M to demonstrate the stability of the resulting Kerr black hole. The early growth of the apparent horizons is a gauge (coordinate) effect.


Fig. 2-1 Evolution at t/M = 0

Fig. 2-2 Evolution at t/M = 220

Fig. 2-3 Evolution at t/M = 270

Fig. 2-4 Evolution at t/M = 440

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BH Kick

The resulting black hole has a substantial recoil velocity of 174 km/s. The following clip contains the period immediately following the merger, which clearly illustrates the black hole's high recoil velocity.

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Evolution of Gravitational Radiation Profile

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 as the BHs maintain a quasicircular orbit. Figures 3-3 and 3-7 show the gravitational radiation profile during the late inspiral and merger stages of our binary black-hole coalescence simulation. Finally, we see a ringdown as the distorted black hole settles down to Kerr equilibrium (Figures 3-4 and 3-8). Both polarization modes (h+ and hx) are shown.

h+


Fig. 3-1 Evolution at t/M = 0

Fig. 3-2 Evolution at t/M = 220

Fig. 3-3 Evolution at t/M = 270

Fig. 3-4 Evolution at t/M = 310

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hx


Fig. 3-5 Evolution at t/M = 0

Fig. 3-6 Evolution at t/M = 220

Fig. 3-7 Evolution at t/M = 270

Fig. 3-8 Evolution at t/M = 310

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Final Black Hole Parameters

Listed in the table below is the dimensionless spin of the black hole at the end of our simulation. Also shown are the radiated energy and angular momentum from gravitational wave emission. Here, M is the initial ADM mass whereas MBH is the final ADM mass of the black hole.

MBH/M0.981
JBH/M2BH0.541
ΔE GW/M0.019
ΔJGW/M20.151
Recoil Velocity174 km/s
δE ≡ (M-MBH-ΔEGW)/M-2 x 10-4
δJ ≡ (J-JBH-ΔJGW)/M9 x 10-4

Our simulation maintains excellent conservation of energy and momentum, since δE and δJ are on the order of 10-4.


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last updated 15 December by aakhan3

Center for Theoretical Astrophysics---University of Illinois at Urbana-Champaign

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