Comparisons
Effects of Black-Hole
Spin
Fixing the mass ratio q = 3 and the initial orbital period, we vary
the initial spin parameter of the black hole from ã = -0.5 to 0.75. We find that for spins
-0.5, 0.0, and 0.75, the binary inspiral phase lasts for 3.25, 4.5, and
6.5 orbits, respectively. As the initial BH spin parameter ã
increases, the total initial angular momentum increases, requiring more
gravitational-wave cycles to emit angular momentum and bring the BH and
NS close enough to merge. Also, as the spin increases, NS tidal
disruption becomes more pronounced, resulting in long tidal tails that
eventually form disks with rest mass ≈ 4% and ≈ 15% the rest
mass of the neutron star, for ã =
0.00 and ã = 0.75,
respectively. Thus BHs with higher spin would likely lead to even more
massive disks. Such disks around rotating BHs are good candidates for
GRB central engines.
Fig. 1-1 Initial Frame |
Fig. 1-2 Final Frame |
Mass Ratio
Comparisons
Fixing the initial spin parameter of the black hole ã = 0, we varied the mass ratio from
q = 1 to 5. For the cases simulated, a
high mass ratio leads to tidal disruption after a higher number of
orbits. For sufficiently high mass ratio, the NS is swallowed by the BH prior to tidal disruption (we do not simulate such a case). The equal mass q = 1 case is
special, and probably does not occur in nature. After tidal disruption, the NS matter curls around the BH
forming a hot, low-density spiral that winds around the apparent horizon and smashes
into the tidal tail, generating a large amount of shock heating. A
fraction of the heated NS matter in the tail losses angular momentum and
falls into the BH. The rest deforms into an inhomogeneous disk before
settling into a quasistationary state. At the end of the simulation, the
NS matter settles into a high density, low temperature torus of matter
surrounding the BH.
Fig. 2-1 Initial Frame |
Fig. 2-2 Final Frame |
last updated 15 December 2014 by aakhan3
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